Certisyn, Inc.

United States of America jhillier@certisyn.com

Security Internet-Draft SCITT RATS attestation reconciliation cross-jurisdictional policy-version agentic-AI friend-or-foe This document specifies the Attestation Reconciliation Protocol (ARP), a deterministic, bilateral, minimum-disclosure mechanism for reconciling verification claims against a plurality of sovereign authoritative registers without raw register records leaving their data-residency jurisdiction. ARP extends the SCITT (Supply Chain Integrity, Transparency, and Trust) architecture to cross-sovereign claim reconciliation. A reconciliation server canonicalises a structured claim, binds the identity of the requesting principal -- including, where the requester is an autonomous agent, a friend-or-foe determination of that agent's verifiable principal binding -- projects the claim through register-specific controlled projection functions producing the nearest permitted ancestor predicate supported by each addressed register, transmits register-specific ciphertexts, receives partial attestations whose payload discloses, of the subject, only a verdict, an optional divergence axis, the applied profile parameters and a query binding digest, aggregates those attestations under a verdict arithmetic the deployment's policy resolves, committing each register's contribution to a Merkle tree, and seals the resulting reconciliation output against a policy-version hash. An append-only cross-jurisdictional settlement-layer ledger records digests and structural metadata, with no claim, register-record or principal content. The protocol supports retroactive re-evaluation of historical reconciliations under updated pattern libraries or policy versions without bilateral renegotiation, and a cryptographic-primitive-upgrade path including post-quantum primitives. This revision adds a normative binding to the SCITT Reference APIs, register data-format profiles for beneficial-ownership, corporate-registry, customs and consolidated-sanctions formats, and a source-data version binding that makes a change in a historical verdict attributable to a change in policy or to a change in the underlying published corpus.

Note to the RFC Editor RFC EDITOR: please remove this section before publication. This document is Standards Track and makes six normative references to Informational documents: RFC 2104, RFC 6234, RFC 6839, RFC 8785, RFC 9053 and RFC 9334. Each is a downref under . RFC 6839, RFC 9053 and RFC 9334 are already recorded in the downref registry, so no Last Call action is required for them. RFC 2104 and RFC 6234 are cited for HMAC and for SHA-256, which every digest this document defines depends on and which earlier revisions used throughout with no normative reference at all; RFC EDITOR, please confirm their current downref-registry status, since it may have changed since this revision was written. RFC 8785 is not registered, and it is the one that needs the announcement below. That reference is deliberately normative: ARP's Canonical Claim is a digest over an RFC 8785 serialisation preceded by Unicode Normalization Form C, and the subject digest of is a digest over an unmodified RFC 8785 serialisation. Neither can be computed without RFC 8785, and an implementation that substituted any other canonicalisation would compute a different value for the same claim. The reference is therefore load-bearing for interoperability and cannot be demoted to informative. This is called out here so that the downref can be noted in the IETF Last Call announcement, which Section 2 of strongly recommends without requiring. This document also makes a normative reference to , which at the time of writing has completed IETF process and is in the RFC Editor queue with no RFC number yet assigned. imposes requirements expressed in terms of that document's endpoints, status codes and media types, and an implementation cannot satisfy them without it, so the reference cannot be informative. RFC EDITOR: this document should not be published before that draft, and the reference should be updated to the resulting RFC number.

Introduction Sovereign authoritative registers record facts that are treated as conclusive within their jurisdiction. Examples include beneficial-ownership registers (such as the United States FinCEN Beneficial Ownership Secure System, the United Kingdom People with Significant Control register, and the European Union beneficial-ownership registers under the Anti-Money-Laundering Directives), corporate registries, consolidated sanctions lists, export-control registers, foreign-ownership-and-control-or-influence registers, maritime vessel registrations, flag-state registers, aviation registrations, land-title registries, customs declarations, and multilateral biometric registers. Institutional decision-makers -- including export-control compliance officers, anti-money-laundering review functions, foreign-investment screening review functions, sanctions-screening operators, multilateral aid distribution authorities, and platform-owned verification infrastructure -- routinely require reliance on facts recorded across two or more sovereign registers simultaneously. Cross-sovereign reliance today faces four structural problems, which this protocol is designed to address in combination:

1. Raw-record disclosure. Existing approaches require the raw register record either to leave its data-residency jurisdiction or to be re-disclosed in plaintext to a relying party in another jurisdiction. Sovereign registers under data-protection regimes are jurisdictionally constrained against such re-disclosure.
2. Non-reconcilable register outputs. Each sovereign register exposes a different schema, a different signing chain, a different verdict semantic, and a different statutory access regime. A relying party that requires a deterministic combined verdict over n sovereign registers therefore faces n parallel verification problems.
3. Non-auditable settlement. Cross-sovereign reliance, where it occurs at all, occurs without a settlement-layer audit trail consumable by sovereign regulators.
4. Unverifiable requester identity in an agentic setting. Cross-sovereign reliance is increasingly initiated not by an authenticated human operator but by an autonomous software agent acting on behalf of a principal. Where the agent's binding to a real, authenticated principal cannot be verified, the reconciliation is performed for an unknown or impersonated party, and the settlement record attributes reliance to no accountable principal. An agent whose principal binding cannot be verified is treated as hostile (zero-trust); the normative rules are in and .

This document specifies ARP, a protocol that addresses all four deficiencies in combination, and is layered atop the SCITT architecture and the RATS architecture . The fourth deficiency is not hypothetical. Where an autonomous agent can act, its containment assumptions may not hold at run time, and a binding between an agent's claimed authority and its actual conduct that is established only after the fact is not a control. The binding must be checkable at the moment of action. ARP is designed for that moment. Forensic reconstruction establishes what an agent did after a consequence has occurred; ARP reconciles an agent's claimed authority and principal binding against authoritative registers while the action can still be refused. A reconciliation that yields a non-decisive or divergent verdict is a control input available before the action commits, not an audit finding available after. This document treats real-time reconciliation of claimed-versus-actual conduct as a first-class property of accountable autonomous action.

Relationship to Other Work This protocol is assembled from existing work wherever existing work reaches, and this section states what it takes, what it does not replace, and why it exists as a separate document rather than as an extension to one of them. A reader who concludes after this section that an existing mechanism already covers the problem has the information needed to say so, which is the purpose of putting it before the specification rather than after it.

What this document builds on The transparency model is . A Reconciliation Output is a Signed Statement in that architecture's sense, the Settlement-Layer Ledger is a Transparency Service, and states the mapping field by field. This document defines no registration API and expects . Receipts are . Where the two disagree, governs and this document is wrong. The evidence-appraisal vocabulary is . states the correspondence between a Reconciliation Output and an Attestation Result, and the Reconciliation Agreement occupies the position of an Appraisal Policy. This document does not define a second appraisal model. Logging and inclusion proofs are . uses the leaf and proof structure without modification. The Merkle constructions here are that construction; the only thing this document adds is what goes into the leaf. Encoding is with where a JSON form is required, and signatures are and . adds determinism requirements over those and defines no new encoding. Requester authentication over HTTP is , and the agentic binding of composes with rather than defining a parallel scheme.

What this document does not replace It does not replace Verifiable Credentials or Decentralized Identifiers, and it is not a credential format. A Reconciliation Output is not held by a subject, is not presented by a subject, and carries no selective-disclosure mechanism for a holder. Where a deployment needs a subject-held credential, that work exists and this document is not it. It does not replace a national register's own API, signing chain or statutory access regime, and it does not ask a register to change any of them. The whole premise of is that registers keep their interfaces. It does not define a trust framework, an accreditation scheme or a policy language. What counts as an acceptable register, an acceptable operator or an acceptable verdict is out of scope and stays with the relying party.

Why it is a separate document The problem in is a relying party requiring a deterministic combined verdict over two or more sovereign registers that will not export their raw records, and requiring a settlement record a sovereign regulator can audit afterwards. Each ingredient of that exists. The combination does not. makes a statement transparent once it has been made, and is deliberately silent on how the statement was produced or whether it reconciles anything. appraises evidence about one attester and does not reconcile the outputs of several independent authorities into one verdict. proves an entry is in a log and says nothing about what the entry means. None of the three is deficient in this. Reconciliation across sovereign registers, under a declared agreement, with non-answers distinguished from negative answers and with a coverage denominator a relying party can check, is a layer above all of them, and adding it to any one of them would push work into that document which its own charter does not cover. The alternative this document rejects, and names so that a reader can disagree with the choice rather than assume it was not made, is a profile of carrying the reconciliation semantics in an unconstrained payload. That is smaller and it fails at the one property the problem requires: a payload a Transparency Service does not interpret cannot carry a verdict two independent verifiers must reach identically. Determinism has to be specified where the verdict is produced.

Where the design was taken from elsewhere Several mechanisms here were established by other people, several of them in review of earlier revisions of this document, and each is named at the point of use as well as in . The Signing Input Digest construction of follows from a reproduction posted to the SCITT mailing list rather than from anything original here. The sweep-every-instance method applied to that construction, and the two-axis separation of the coverage vocabulary, are likewise attributed where they are used. A specification that presents a borrowed design as its own invention is defective independently of whether the design is sound, and the naming is normative practice in this document rather than courtesy.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. The following terms are defined for use throughout this document:

Sovereign Register:

An authoritative data store maintained by or on behalf of a sovereign and treated as conclusive within that sovereign's jurisdiction for the predicates the register is empowered to record.

Register Operator:

The entity that operates the Sovereign Register and is contractually empowered to bind the register's attestations.

Bilateral Register Agreement:

A negotiated contractual instrument between the operator of the reconciliation server and a Register Operator, declaring the terms under which a register is addressable under this document. enumerates the items an Agreement MUST declare, in the order that fixes them, and defines the Agreement Hash each Agreement carries.

Witness Set:

The set of observers, declared in a Bilateral Register Agreement under , whose Head Consistency Statements under and Witness Linkage Segments under constitute head-consistency evidence independent of the responding service.

Witness Linkage Segment:

A signed record, published by a witness at its own origin under , of the linkage arrays it observed over a contiguous interval of Entry Sequence Numbers. Consecutive Segments from one witness cover a Ledger from that witness's Attestation Floor upward, and are what a relying party assembles a chain between two heads from where obliges it to hold one.

Witness Quorum:

The number of Witness Entries, as defines them, with pairwise distinct Operating-Party Identifiers whose head-consistency evidence a relying party must hold before the evidence condition of is satisfied. Declared under and evaluated under , which states what that evidence is in each of its two branches.

Policy-Epoch Store:

The persisted, versioned record of a deployment's verification-policy state, from which the Policy-Version Hash of is reconstructible and from which the reconciliation server resolves, per predicate and named regime set, the Verdict Arithmetic and its parameters and the reliance interval. It holds the Deployment Blinding Value and the Requester-Binding of each reconciliation. It is internal to the reconciliation server; this document constrains what it must be able to answer and not how it is built.

Requesting Principal:

The accountable party on whose behalf a reconciliation is performed. A Requesting Principal is either an authenticated human or institutional operator, or an autonomous agent carrying a Verified Principal Credential that binds it to such an operator.

Requesting Agent:

An autonomous software agent that initiates a reconciliation. A Requesting Agent is FRIENDLY when it carries a verifiable identity -- a request signed under HTTP Message Signatures per Web Bot Auth , a genuinely verified declared bot, or a Verified Principal Credential -- and ENEMY when its principal binding is absent or unverifiable. Anything unverifiable is treated as ENEMY.

Verified Principal Credential:

A cryptographic credential asserting that a named, authenticated principal stands behind a request, verifiable without contacting the credential issuer in the reconciliation hot path. A Verified Principal Credential MAY be carried in any COSE-enveloped structure binding the claim, its evidentiary provenance, and the principal's credential, or in any equivalent verifiable-credential form .

Agent Friend-or-Foe (IFF) Determination:

The deterministic classification of a Requesting Agent as FRIENDLY or ENEMY, computed from the presence and cryptographic validity of a verifiable agent identity and, where required by policy, a Verified Principal Credential. The determination is recorded in the Requester-Binding field and committed to the Policy-Version Hash.

Canonical Claim:

A deterministic structured representation of a verification claim, comprising at least a subject identifier, a predicate, an attested value, an applicable-regimes set, and an evidentiary provenance manifest. Canonicalisation is performed in the following order, which is normative because the operations do not commute:

1. Unicode Normalization Form C is applied to every string value and to every object member name.
2. Object member names are sorted by UTF-16 code unit, as specified in Section 3.2.3 of .
3. Declared array order is preserved.
4. Numbers are rendered as specified in Section 3.2.2.3 of .
5. A member whose value is absent is omitted, rather than serialised with a null placeholder.

Steps 1 and 2 are order-dependent and observably so: for an object carrying the member names "A" followed by COMBINING RING ABOVE (U+0041 U+030A) and "B", normalising before sorting and sorting before normalising yield different serialisations and therefore different Claim Hashes. This specification requires normalisation first. The member-sort code unit is normative. An implementation that sorts by Unicode code point rather than by UTF-16 code unit produces a different Claim Hash for any object carrying a member name outside the Basic Multilingual Plane. The two orderings are not interchangeable, and this specification pins the UTF-16 reading, which is the one Section 3.2.3 of specifies. This construction is NOT the construction defined in for subject_digest. The two MUST NOT be substituted for one another; see .

Predicate Taxonomy:

A controlled hierarchical classification of predicates that may be the subject of reconciliation, enabling taxonomic prefix match in projection. The taxonomy includes an agent: branch whose predicates reconcile the verifiability of an agent's binding to a principal (for example agent:principal-binding-verifiable and agent:credential-attested).

Per-Register Claim Projection:

The narrowest structured query sufficient to elicit the required Partial Attestation under a register's Bilateral Register Agreement, computed by the controlled projection function as the nearest ancestor of the Canonical Claim Predicate that is a member of the register's permitted-predicate set. Where the taxonomy admits more than one such ancestor, the projection MUST fail rather than choose.

Partial Attestation:

A cryptographically signed output produced by a Sovereign Register in response to a Per-Register Claim Projection. The Partial Attestation payload SHALL disclose, of the subject, only a Reconciliation-Verdict field, an OPTIONAL Divergence-Axis field, the applied parameters of and the Query Binding, which is a digest; it SHALL NOT disclose any register record. Fields denoting state rather than the subject -- the Freshness Timestamp, and the Source-Data Version Identifier of -- are enumerated in .

Applicable-Regimes Set:

The set of regulatory regimes a Canonical Claim names as applicable. It is a claim field chosen by the requester and states which law the requester asserts governs the question. It does not carry the Verdict Arithmetic, its parameters or the reliance interval; those are resolved by the reconciliation server from the policy-epoch store of , keyed on the predicate and the named regimes, and are committed to the Policy-Version Hash. A requester names the regime; the deployment's policy determines how evidence under it combines and how long a verdict may be relied upon.

Combined Verdict:

The single verdict value produced by aggregating the Reconciliation-Verdict fields of the Per-Register Result Set of under the Verdict Arithmetic resolved under . Its values are match, no-match, partial-match and indeterminate. The decisive values are match and no-match.

Reconciliation Hash:

The SHA-256 digest of over the deterministically encoded CBOR serialisation of a Reconciliation Output excluding its Sealing Signature and Sealing-Key Identifier, as specified in , and with every signature made by a party other than the sealing reconciliation server replaced by the Signing Input Digest of that signature. Those are the register signature carried in each Query Binding Record, the register signature carried in each Non-Answer Statement, and the authorising operator's signature carried in the Override Record of . Excluding the Sealing Signature is not sufficient on its own: a Reconciliation Output embeds signatures made by parties other than the server, and a digest over those names whichever encoding the reader was handed, for the reason gives. The rule is stated over the class -- every signature not made by the sealing server -- and not over an enumeration, because an enumeration is complete only until a field is added, and the Override Record is the field that showed this.

Authority Origin:

The serialisation of an origin as Section 6.2 of defines it: the scheme, the U+003A COLON and two U+002F SOLIDUS characters, the host, and, where the port differs from the default for the scheme, a U+003A COLON and the port in decimal with no leading zeros. The scheme and the host are lowercased. There is no trailing solidus, no path, no query and no fragment, and no userinfo component: https://register-a.example and https://register-a.example:8443 are Authority Origins and https://register-a.example/, https://Register-A.example, https://register-a.example:443 and register-a.example are not. An implementation MUST reject a value in any of those other forms rather than normalise it, because a value that is normalised on receipt is a value two parties can hash differently before they compare it. This document uses Authority Origins as bytewise sort keys inside signed sets, as path segments, and as equality targets against the origin component of a Sealing-Key Identifier. Each of those three uses breaks on a different divergence: a sort key reorders, a path segment resolves elsewhere, and an equality test refuses a key that was in fact authorised. Fixing the form once, here, is what makes those three uses one term.

Signing Input Digest:

The SHA-256 digest over the deterministically encoded CBOR Sig_structure of a COSE_Sign1, as Section 4.4 of constructs it: the array of the context string "Signature1", the protected header, the external additional authenticated data, and the payload. It is a digest of what the signer signed and not of the envelope carrying it, so it does not depend on the signature bytes and does depend on the protected header, which in this document carries the key identifier and the algorithm identifier under . This document supplies no external additional authenticated data: the third element is the zero-length byte string in every Sig_structure it defines, and an implementation MUST NOT supply another value, because a Signing Input Digest a third party cannot reproduce is not an identifier. The protected header is taken as the byte string transmitted and MUST NOT be re-encoded; those bytes are the signer's and are what the signature covers. Every digest in this document that identifies or chains a signed artefact is a Signing Input Digest, for the reason gives.

Divergence Axis:

A controlled descriptor identifying a structural qualification on a verdict. Most identify the reason for a non-match; those recorded by the reconciliation server may qualify a verdict of any value. The controlled set is the registry of , which at the time of writing comprises identity-mismatch, jurisdictional-scope-mismatch, temporal-mismatch, ownership-threshold-mismatch, sanctions-list-match, register-record-absent, claim-predicate-unsupported, claim-projection-narrowed-beyond-attestation-scope, agent-principal-unverifiable, agent-credential-absent, agent-impersonation-suspected, agent-action-scope-divergence (the authorised scope attested for an agent action and the actual conduct attested for it do not reconcile), source-version-skew, register-threshold-divergence (two registers answered the same predicate under different declared interest thresholds, per ), declared-not-determined (the register could answer only over a declared fact where the claim ranged over a determined one, per ), and freshness-stale. Divergence Axes recorded by the reconciliation server rather than by a register, which the registry marks as such and which initially are freshness-stale, source-version-skew, register-threshold-divergence, declared-not-determined and agent-action-scope-divergence, are carried in the Reconciliation Output, not in the register's signed Partial-Attestation payload.

Source-Data Version Identifier:

An identifier denoting the state of a published corpus, external to both the Bilateral Register Agreement and the Policy Version, against which a register evaluated a Projected Predicate. A consolidated sanctions list is the characteristic case. Its purpose is attribution: without it, a change in a historical Combined Verdict cannot be attributed to a change in policy state rather than to a change in the underlying corpus. Requirements are in .

Post-Seal Evaluation Qualifier:

A controlled descriptor identifying a condition arising after a Reconciliation Output has been sealed, carried in a Post-Seal Evaluation Record per rather than in the Output. The values are those of the registry in , at the time of writing notarisation-incomplete and attribution-indeterminate. A Post-Seal Evaluation Qualifier is not a Divergence Axis: a Divergence Axis qualifies a verdict, and a Post-Seal Evaluation Qualifier qualifies an operation on an Output whose verdict is already fixed.

Threshold-Sensitive Predicate:

A Predicate whose truth depends on an interest threshold, so that two registers evaluating it under different declared thresholds are not answering the same question. A profile registered under MUST state which of its predicates are threshold-sensitive.

Source Class:

A partition of the Addressed-Registers Identifier Set resolved for the named regimes under , over which source-class-quorum is evaluated.

Sovereign Re-Notification:

A signed notification emitted through the Regulator Portal to each regulator whose statutory scope covers a reconciliation whose historical Combined Verdict has materially changed. The supersession that occasions it is separately recorded as a continuation-supersession entry on the Settlement-Layer Ledger under , so that a relying party that acted on the superseded Output can discover the change.

Reconciliation Nonce:

A value of at least 128 bits drawn from a cryptographically secure random source, unique to one Per-Register Claim Projection and therefore to one register within one reconciliation. It is never reused. Two registers addressed in the same reconciliation receive different nonces, so their Query Bindings differ even where the Projected Predicate and Subject Reference are identical, and an attestation elicited from one register cannot be presented as an answer from another.

Source-Version Skew:

The condition, recorded as source-version-skew, in which two Partial Attestations answer the same Projected Predicate against different states of the same published corpus. Both are within their freshness windows; the skew is in the corpus, not in the attestations. It is not a disagreement, and an implementation MUST NOT treat it as one.

Attribution Indeterminate:

The Post-Seal Evaluation Qualifier, recorded as attribution-indeterminate, in which a Retroactive Evaluation cannot determine whether a material change in a historical Combined Verdict arose from a change in policy state or from a change in Source-Data Version. It is a statement about the evaluation, not about any register's answer.

Reconciliation Output:

A data structure aggregating Partial Attestations from a single reconciliation event, sealed against a Policy-Version Hash.

Verdict Arithmetic:

The operator governing how per-register verdicts combine into the Combined Verdict, specified in . The controlled set comprises conjunction, disjunction, threshold-count and source-class-quorum.

Hash-Linkage Aggregation:

An aggregation of Partial Attestations in which the per-register attestations are reduced to their Signing Input Digests, ordered, committed to a Merkle tree, and emitted with a Merkle root and a per-register verdict band. The Merkle commitment and its inclusion proofs MAY be encoded as COSE Receipts .

Policy-Version Hash:

A cryptographic commitment to the canonical verification-policy state in force at the moment of reconciliation, including reconciliation rules, threshold parameters, pattern-library version, applicable-regimes precedence, verdict-arithmetic selection with every parameter it takes, the reliance interval, the Agent-IFF policy in force, the Requester-Binding, and the Bilateral-Register-Agreement Hashes of the addressed registers.

Settlement-Layer Ledger:

An append-only cross-jurisdictional log retaining hashes of reconciliations and no Canonical-Claim, register-record or principal content. It carries entries of two kinds, discriminated by an entry type: a reconciliation entry, which records a sealed Reconciliation Output, and a Continuation entry, which records a notarisation outcome, a Post-Seal Evaluation Record or a supersession arising after that Output was sealed. Every entry carries a sequence number, the entry type, the claim hash, the reconciliation hash, an entry timestamp, a prior-entry hash, a self-entry hash and an entry signature; the fields each kind carries in addition are enumerated in . A Continuation entry may also carry a transparency-service identifier, an entry identifier, an HTTP status code, a post-seal evaluation record hash, a material-change indicator, a superseding reconciliation hash and a superseding entry sequence number. Not every field is a digest -- the sequence numbers, the timestamps, the entry type, the descriptors and the indicators are not -- but no field carries Canonical-Claim, register-record or principal content, and no field is a retrieval address.

Audience Set:

The set of Audience Members of a Reconciliation Output, sealed with it under . Each Audience Member is an accountable-principal identifier together with a verification method that can be presented after the reconciliation. The Requesting Principal is a member wherever it can be identified. Entitlement to read about a reconciliation follows membership, not possession of the artefact.

Reliance Horizon:

The time after which an Audience Member MUST NOT treat a Combined Verdict as current without reading the Continuation entries for its Reconciliation Hash. It is the Reconciliation Timestamp advanced by the reliance interval that deployment policy declares for the predicate and the named regimes, resolved as resolves the Verdict Arithmetic. It bounds reliance and does not affect the validity of the Sealing Signature.

Ledger Head Statement:

A signed statement of the current head of the Settlement-Layer Ledger, published at a well-known URI and notarised at a declared interval, comprising the head's Entry Sequence Number, its Self-Entry Hash, its Entry Timestamp, the time the Statement was produced, and a pointer to the most recent completed head notarisation. Defined in .

Evaluation Sweep Statement:

A signed record that a retroactive evaluation was performed, comprising the trigger, the policy state applied, the ledger head at the start and end of the sweep, the counts examined and materially changed, a Merkle root over the Claim Hashes examined, a timestamp, a pointer to the notarisation of the previous Statement. Defined in . Its purpose is to make an evaluation that never ran a signed omission rather than a silence.

Non-Answer Statement:

A statement signed by a register recording that it declined to answer, over the Reconciliation Identifier, the Projected Predicate, the Subject Reference, the Reconciliation Nonce and the reason. Required wherever a Non-Answer Reason is register-attested, per .

Architecture ARP comprises seventeen subsystems arranged as a deterministic pipeline:

1. Canonical Claim Ingestion
2. Requester Identity Binding and Agent Friend-or-Foe Gate
3. Adversarial Pre-Transmission Test
4. Per-Register Projection Function, under the profile of declared in the Bilateral Register Agreement
5. Per-Register Encryption
6. Partial-Attestation Reception, including Source-Data Version Binding
7. Non-Answer Resolution
8. Verdict Re-Typing
9. Aggregation under the Verdict Arithmetic, per
10. Policy-Version-Hash Sealing
11. Settlement-Layer Ledger Write
12. Notarisation under , where performed
13. Regulator Portal
14. Retroactive Evaluation
15. Output Delivery under
16. Post-Seal Evaluation Recording
17. Cryptographic-Primitive-Upgrade Path

Given an identical Canonical Claim, an identical Requester-Binding, an identical Audience Set, an identical Addressed-Registers Identifier Set, identical Bilateral-Register-Agreement Hashes for the addressed registers, an identical Pattern-Library Version Identifier, and an identical Policy-Version Identifier, the system MUST produce Reconciliation Outputs identical in every field save those enumerated below as outside this requirement, and identical Claim Hash and Policy-Version Hash values in the corresponding Settlement-Layer Ledger entries. The Reconciliation Hash is deliberately not among those values. It is a content commitment over one sealed Output, taken over a preimage that includes that Output's Reconciliation Timestamp, and it is not reproducible across runs; the Reconciliation Identifier of is the reproducible index, and it is the Claim Hash and Policy-Version Hash that make it so. Requiring an identical Reconciliation Hash would require an identical timestamp, which no implementation can deliver. The per-event fields of a Ledger entry -- Entry Sequence Number, Entry Timestamp, Prior-Entry Hash, Self-Entry Hash and Entry Signature -- are position-dependent by construction and are outside this requirement; the Entry Signature is further outside it because a signature scheme is not required to be deterministic. Within the Reconciliation Output itself the Reconciliation Timestamp, the Reliance Horizon computed from it, the Sealing Signature and any Override Record are outside it: the first is per-event, the second need not be deterministic, and an Override Record records an operator's discretionary act rather than a function of the enumerated inputs. The register-produced signatures the Output carries -- the Partial Attestation inside each Query Binding Record, and each Non-Answer Statement -- are outside it on the same ground as the Sealing Signature: they are signatures, and a signature scheme need not be deterministic. So is the Sealing-Key Identifier, which is rotation state and not an enumerated input. So are the Reconciliation Event Identifier, the Reconciliation Identifier that carries it, and every Reconciliation Nonce carried in a Query Binding Record or a Non-Answer Statement, together with the register signatures taken over them: each is drawn fresh per reconciliation and is uniqueness state rather than an enumerated input. Two reconciliations agreeing on every enumerated input MUST differ in all three, and an implementation MUST NOT read that difference as a determinism failure. Stating it matters because the requirement above is expressed as identity in every field save those carved out here, so a field that is necessarily fresh and not carved out makes the requirement unsatisfiable by any implementation. So are attestation-stale and register-unresponsive, and the Divergence-Axis and verdict consequences that follow from either: both are functions of wall-clock timing and network conditions rather than of the enumerated inputs, which is the same ground on which the Freshness Timestamps themselves are outside it. A reconciliation driven to a query-budget-exhausted or subject-ceiling-exhausted Non-Answer Reason under is also outside it, because the budget is accumulated state and not an enumerated input. The residual risk that carve-out creates, and why this document does not close it, is set out in . The Freshness Timestamps of the constituent Partial Attestations, and any Source-Data Version Identifiers they carry per , are likewise outside it: both denote state external to the enumerated inputs. Two reconciliations agreeing on every enumerated input but differing in Source-Data Version are not required to agree field for field, and an implementation MUST NOT treat such a difference as a determinism failure.

Canonical Claim Ingestion A Canonical Claim comprises:

• Subject Identifier
• Predicate (drawn from the controlled Predicate Taxonomy)
• Attested Value (in the canonical type for the Predicate)
• Applicable-Regimes Set
• Evidentiary Provenance Manifest
• Claim Timestamp ( UTC)
• Claim Hash: the SHA-256 digest over the deterministically encoded CBOR array ["arp-claim-v1", Deployment Blinding Value, canonical serialisation], where the canonical serialisation is the form of the preceding fields as constructs it, carried as a CBOR byte string. Framing the blinding value as an array element rather than concatenating it is what stops two deployments differing on order, separator or length prefix while claiming the same construction identifier

The reconciliation server MUST verify, before computing the Claim Hash, that the octets it received under are the canonicalisation of the claim they carry. It MUST parse them, re-serialise the parsed fields as this section constructs them, and refuse a request whose received octets differ from that re-serialisation, or whose member set is not exactly the fields enumerated above, returning the 422 of with a Remediation Advisory naming the difference. has the requester supply the serialisation as a byte string and has the server hash the octets it received, for a reason that is correct: re-serialising a natively encoded claim would let two servers receiving identical bytes compute different Claim Hashes. The consequence not drawn was that the preimage of the Settlement-Layer Ledger index is then chosen by the requester. A claim submitted in NFD and the same claim in NFC have identical canonical field values and produce two Claim Hashes, two ledger indices and two retroactive-evaluation keys, and a sweep selecting on one misses the other. The check above keeps the requester's octets as the preimage and makes them canonical, which is what the rest of this section already assumes of them. The same argument appears at for the Authority Origin -- a value normalised on receipt is a value two parties hash differently before they compare it -- and it was applied there and not here. Two claims whose canonical field values are identical MUST produce the same canonical form, and the same Claim Hash within one deployment. Across deployments the Claim Hash differs by the Deployment Blinding Value while the canonical form does not. Declared array order is significant; claims differing only in declared array order are distinct claims. The Claim Hash is the index on the Settlement-Layer Ledger and the key for retroactive re-evaluation. The Evidentiary Provenance Manifest is a JSON object, and this document does not otherwise constrain its members. It MUST NOT carry a signature, a COSE_Sign1, or any other signed artefact, in any member at any depth, and a reconciliation server MUST refuse a claim whose Manifest carries one, returning the 422 of . Where the evidentiary provenance is itself a signed artefact -- a COSE-enveloped evidence structure, or a Verified Principal Credential -- the Manifest carries the Signing Input Digest of that artefact, rendered as a lowercase hexadecimal text string, and the artefact travels outside the Canonical Claim. The Manifest is a field of the Canonical Claim and therefore inside the Claim Hash preimage, so a signature within it is a signature inside a digest preimage, re-encodable in transit by a party holding no key, for the reason gives. A claim carrying one indexes the Settlement-Layer Ledger under a value that moves while the claim does not, and no party outside the deployment can detect it, because the Claim Hash is blinded and cannot be recomputed outside the deployment at all. This is the seventh carrier and the only one the class rule of could not have reached. That rule directs a party computing a digest to substitute a Signing Input Digest for any signature made by another party, and it is inoperable here for two reasons: the preimage is JSON, which has no byte-string type for the substituted value, and has the server hash the requester's octets, so a server-side substitution would produce a Claim Hash over bytes the requester never signed. Where a construction cannot be repaired by the general rule, the content has to be excluded rather than the rule extended, which is what the prohibition above does. An earlier revision instead said the container form "does not alter the Claim Hash", which is true of the container and false of what the container holds.

Requester Identity Binding and Agent Friend-or-Foe Gate Before the Adversarial Pre-Transmission Test, the reconciliation server MUST establish the identity of the Requesting Principal and record it in a Requester-Binding field. The Requester-Binding comprises a requester-binding class, the identifier of the accountable principal where known, and a reference to the verification method used. The class is one of:

• human-operator, where an authenticated human or institutional operator is the accountable principal.
• agent-verified, where an agent's signing key verified AND the principal it asserts was corroborated by a reconciliation under or by a Verified Principal Credential whose status was checked.
• agent-key-verified, where an agent's signing key verified but the principal it asserts was not corroborated.
• agent-unverified, where the request was signed under a bare key that resolves to no signature-agent card, carries no Verified Principal Credential, and asserts no principal. The key gives continuity of identity between requests and nothing else, which is why it is a class and not a refusal; a request that carries no verifying signature at all is not admitted, by .

agent-key-verified exists because possession of a key and binding to a principal are different facts and earlier revisions recorded them as one. An agent that signs correctly under a Web Bot Auth key has demonstrated that it is the same agent as last time; it has not demonstrated that any accountable party stands behind it. Recording that state as agent-verified overclaims to every downstream reader, and recording it as agent-unverified discards a real and useful fact. A relying party that requires an attributable principal should treat agent-key-verified as it treats agent-unverified; one that requires only continuity of identity may treat it as it treats agent-verified. This document states no requirement on a relying party's own risk policy; what it requires is that the two states be recorded distinctly so that the policy can be applied. The Agent-IFF policy states which reconciliations may be decisive at each class. Where the requester is an autonomous agent, the server MUST perform an Agent Friend-or-Foe (IFF) Determination. An agent is classified FRIENDLY only where at least one verifiable identity is present and cryptographically valid: a request signed under HTTP Message Signatures with a key resolvable through a Web Bot Auth signature-agent card , advertised via the Signature-Agent header , which also defines the key directory it names, a genuinely verified declared bot, or a Verified Principal Credential. An agent presenting no such identity, or an identity that fails verification, MUST be classified ENEMY. The Agent-IFF policy in force declares, per predicate class, whether an ENEMY requester is refused outright, permitted only for non-decisive advisory reconciliation, or permitted with the requester-binding class recorded as agent-unverified, and whether an agent whose key verified but whose principal was not corroborated -- class agent-key-verified -- may reach a decisive verdict. The server MUST NOT silently upgrade an ENEMY requester to FRIENDLY. The Requester-Binding and the Agent-IFF policy identifier are committed to the Policy-Version Hash so that the settlement record is attributable to a determined requester class.

Adversarial Pre-Transmission Test Before any Per-Register Claim Projection is produced, the Adversarial Pre-Transmission Test Subsystem applies the current Pattern Library to the Canonical Claim. The Pattern Library enumerates structural evasion patterns against the projection and aggregation mechanisms of this protocol, including projection-narrowing-evasion, predicate-substitution-evasion, attested-value-bracketing-evasion, addressed-register-cherry-picking, agreement-staleness-injection, pattern-library-version-pinning, and agent-principal-spoofing (an unverifiable agent asserting a principal binding it does not hold). The Subsystem emits either a Pass result or a Remediation Advisory. A Remediation Advisory comprises:

• a Refusal Ground, one of pattern-matched, regime-not-admitted, audience-member-not-enrolled or agent-iff-refused
• the identifiers of the Pattern Library patterns that matched, and the narrowing or substitution each concerns, present exactly where the Ground is pattern-matched
• the regime, the Audience Member Identifier or the Agent-IFF ground the other three Grounds concern respectively, present under the corresponding Ground

It is encoded as a CBOR array in that field order under the media type registered in , absent fields as CBOR null, and is returned to the requester as provides. No projection is transmitted and no Reconciliation Output is produced. The Advisory is the only artefact a refused requester receives, so it carries the ground rather than leaving the requester to infer it. Where the Ground is pattern-matched, the second field MUST be encoded as CBOR null in the Advisory returned to the requester, the array's field order being unchanged, and the matched identifiers and the narrowing or substitution each concerns MUST be retained by the server and disclosed only to a regulator under and to an Audit Identity under . A requester that can vary a claim and read back which pattern matched enumerates, one refusal at a time, the corpus declines to disclose even to a register. The query budget does not bound the probe, being keyed per principal per subject, so an evader varying subjects probes without limit. An Advisory that names the pattern is a more efficient route into the Pattern Library than the Library's confidentiality is a defence of it, and the party it was handed to is the one party the Test exists to defend against. The Per-Register Encryption Subsystem MUST architecturally withhold external transmission until a Pass result has been emitted or until an authorised operator has explicitly overridden the outcome. An override MUST be recorded in the Reconciliation Output as an Override Record and is thereby covered by the Sealing Signature. An override that left no artefact would be indistinguishable from a Pass to every external party, which would make the only manual bypass of the protocol's own adversarial gate invisible to the regulators that gate exists to serve. An Override Record comprises:

• the identifiers of the Pattern Library patterns that matched
• the Pattern-Library Version Identifier under which they matched
• the Override Ground, drawn from the registry of
• the identifier of the authorising operator
• an Override Timestamp ( UTC)
• a signature by the authorising operator, a COSE_Sign1 whose payload is the CBOR array of the fields above in the order listed with the signature position encoded as CBOR null, encoded under Section 4.2.1 of , and carrying as its key identifier the JWK thumbprint, computed as in , of a key published in the reconciliation server's Operator Key Set at /.well-known/arp-operator-keys on its Authority Origin. That key set is published and validated as the sealing key set of is, save that the Authorised-Origin Document MUST name a key identifier for the operator key set distinct from the one anchoring the sealing key set. Sealing keys and operator keys are separate sets because they are held by different parties for different purposes: a server able to sign an override with its sealing key could manufacture an operator's authorisation, and a server holding the only key that anchors its own operator key set could do the same one level up

The signature is by the operator and not by the server. A record the server signs attests only that the server says an operator authorised the bypass; a record the operator signs is a statement the operator made and cannot later disown, which is what a manual override of an adversarial gate has to be for the regulator reading it. The Override Ground is drawn from a registry so that grounds are enumerable and comparable across deployments rather than free text that no reviewer can aggregate. The reconciliation entry that records an overridden reconciliation carries an Override Indicator, so that a regulator reading the Ledger under can see that a bypass occurred without holding the Output. Having seen it, the regulator reads the Output itself under or through the entitlement its statutory scope gives it, and reads the Record. An Override Record visible only to the Audience Set the operator chose to serve would be invisible to the party the mechanism exists for, which is the failure this paragraph and the Indicator together close. The Record names an operator in the clear, in an artefact whose Policy-Version Hash is blinded under precisely to keep principal identities out of reach. That is not a contradiction: blinding protects the Ledger, which is published, and the Reconciliation Output is confidential to its Audience Set under . An override is a discretionary act by a named human against a named pattern, and the parties entitled to the Output are the parties entitled to know who performed it. Nothing about the override reaches the Ledger except through the Reconciliation Hash, which is a digest.

Per-Register Projection Function For each addressed register, the controlled projection function MUST inspect the Canonical Claim against the permitted-predicate set declared in the Bilateral Register Agreement. Where the Canonical Claim's Predicate is directly a member of the permitted-predicate set, the Projected Predicate equals the Canonical Claim Predicate. Where it is not, the projection function resolves the Predicate through taxonomic prefix match: walking the Predicate Taxonomy upward from the Canonical Claim Predicate until reaching a Predicate that is a member of the permitted-predicate set. Where the walk reaches more than one such Predicate at the same taxonomic distance, the projection MUST fail with projection-ambiguous rather than choose between them. Where the walk reaches the taxonomy root without finding one, the projection MUST fail with projection-unsupported. The narrowing operation MUST be recorded in the Narrowed-From field of the Per-Register Claim Projection. The Predicate Taxonomy over which that walk is performed is the union of the branches the Register Data-Format Profiles of define, each branch's parent relation being the one its profile declares and each branch's root being the predicate that profile names as such. Taxonomic distance is defined only between predicates within one branch. A predicate belonging to no declared branch has no parent, and a walk that would leave the branch it began in MUST fail with projection-unsupported. The agent: branch of is governed by no profile and is therefore flat: its predicates have no parent and a walk beginning at one MUST fail on the same reason. There is no registry of predicates and this document does not create one. The taxonomy is a deployment artefact assembled from declared profiles, which is what makes it checkable by the register: the permitted-predicate set is item 1 of and is therefore inside the Agreement Hash, so the second party to a projection can test the walk against terms it negotiated. Earlier revisions named the taxonomy and left the reader to infer where its edges came from. A Per-Register Claim Projection comprises:

• Reconciliation Identifier
• Register Identifier
• Projected Predicate
• Subject Reference, in the form the addressed register's Bilateral Register Agreement declares
• Attested Value, where the Projected Predicate takes one
• Narrowed-From, absent where the Projected Predicate equals the Canonical Claim Predicate
• Bilateral-Register-Agreement Hash
• Policy-Version Hash
• Freshness Window, as declared in the Bilateral Register Agreement
• Reconciliation Nonce
• Profile Parameter Set, being the values the Bilateral Register Agreement declared under that the register is to apply
• OPTIONAL Requester-Binding Class, present exactly where the Bilateral Register Agreement requires it under , disclosing the class and not the principal

A Per-Register Claim Projection is encoded as a CBOR array in the field order above, an absent OPTIONAL or conditionally absent field encoded as CBOR null so that position is preserved. This is the only structure a sovereign register receives, and it is enumerated here so that its contents are determinate and its digest constructions reproducible. The wire binding over which it is transmitted is not specified by this document. This document specifies what the channel must achieve -- the structure it carries, the confidentiality and authenticated-additional-data properties of , and the Query Binding the register signs over -- and leaves the transport, the endpoint, the framing and the concrete encryption construction to be declared in each Bilateral Register Agreement. That is a deliberate scoping decision and it is a real limitation, stated here rather than left to be discovered: two reconciliation servers addressing the same register do so over channels the register defined, so ARP is interoperable in its artefacts and not yet in that leg's transport. Specifying it -- an endpoint, a media type, and a COSE_Encrypt construction pinning the AEAD and the ordering of its authenticated additional data -- is the principal item of work this revision leaves for the next. The register does not receive the Canonical Claim, the Addressed-Registers Identifier Set, or any other register's projection. The register echoes the Policy-Version Hash in its Partial Attestation; it does not compute it, and it is not required to be able to. The reconciliation server MUST send the same Policy-Version Hash to every addressed register in one reconciliation, and MUST verify on reception that each Partial Attestation echoes it. A mismatch MUST be treated as a refusal by that register and recorded under . Without this the per-register signatures over the Policy-Version Hash -- the only independent corroboration of it -- would be discarded at aggregation, and a server could address different registers under different policy versions undetectably.

Subject Mapping Record The projection function transforms the Canonical Claim's Subject Identifier into a Subject Reference in the form the addressed register's Bilateral Register Agreement declares. Until this revision nothing recorded that transformation, nothing constrained it, and no party outside the reconciliation server could check it. That is the gravest thing a reader can fail to notice about an Output. Every signature in a Reconciliation Output can verify, every Query Binding can recompute, the Merkle Root can be correct, the ledger entry can chain and the notarised Signed Statement can pass every check in , while every addressed register answered honestly and completely about a different person. The registers answer about the Subject Reference they were sent. The Output is read as an answer about the Subject Identifier in the claim. Nothing joined the two, and a substitution at that step is invisible to the requester, to an Audience Member, to a regulator reading the portal, to an Audit Identity, and to the registers themselves, none of which is shown the Canonical Claim. Each Per-Register Result Set entry for which a projection was transmitted MUST therefore carry a Subject Mapping Record: the two-element CBOR array of the Subject Reference transmitted to that register, and the Subject Mapping Descriptor -- a text string, drawn from the registry of , naming the transformation applied. The initial registrations are identity, where the Subject Reference is the Subject Identifier unchanged; profile-declared, where the transformation is the one the register's declared Data-Format Profile specifies for the Subject Identifier's form; and agreement-declared, where the Bilateral Register Agreement declares the transformation as one of its terms. A registration MUST specify a transformation that is a function of the Subject Identifier and of declared terms alone, so that a party holding the Canonical Claim and the applicable Agreement can recompute the Subject Reference and compare it. The designated expert MUST refuse a registration whose transformation takes any input the server chooses at reconciliation time, since such a descriptor would name the discretion rather than remove it. A verifier holding the Canonical Claim MUST recompute the Subject Reference under the named descriptor and MUST reject the Output where the recomputed value differs from the one carried. A verifier not holding the Canonical Claim cannot perform that check, and this document does not claim otherwise: what the record gives that party is an attributable statement, signed and sealed and ledgered, of which subject each register was actually asked about. The substitution remains possible and stops being deniable, which is the same trade makes for a suppressed register answer. This does not close the case where the Subject Identifier in the claim was already the wrong person. Nothing in a reconciliation protocol can, and states the boundary.

Register Data-Format Profiles A Bilateral Register Agreement MUST declare the data format in which the addressed register expresses the facts the permitted-predicate set ranges over. The projection function of operates on predicates, not on records; a format profile is what lets an implementer determine which predicates a given register can actually answer, and what a narrowing means against that register's own structure. A profile is a property of a data format, not of a register. It states, for the format it covers, how a permitted predicate is expressed and what the Predicate Taxonomy's parent relation corresponds to in that format. Parameters that vary between registers using the same format -- interest thresholds, maximum chain depths, the set of named lists and the identifiers a register uses for their states -- are not properties of the profile and MUST be declared in the Bilateral Register Agreement. A profile MUST enumerate the parameters a Bilateral Register Agreement declaring it is required to supply, and MUST state which of its predicates are threshold-sensitive per , on which the third re-typing ground of turns. Without that split a single registered identifier would carry facts that differ between registers, and two registers using the same format under different thresholds could not both declare it. A profile MUST NOT introduce a means of transporting register records; profiles constrain predicate expression only. The vocabulary documents a profile names are informative to this document and normative to an implementation of that profile: an implementation cannot evaluate a projection expressed in a vocabulary without it. A profile MUST pin the dated version of each vocabulary it names. This document defines four profiles, with the identifiers registered in :

• arp-profile-bods ()
• arp-profile-corporate-org ()
• arp-profile-customs-wco ()
• arp-profile-sanctions-consolidated ()

Identifiers beginning x- are reserved for bilateral use and MUST NOT be registered. A Bilateral Register Agreement MAY declare one. Each of the four profiles below states the dated vocabulary it uses where it names one, the parent relation for each branch of its predicate space over which narrowing is defined, the parameters a Bilateral Register Agreement declaring it must supply, and which of its predicates are threshold-sensitive within the meaning of .

Beneficial ownership: BODS For registers expressing beneficial ownership as records, the permitted-predicate set is expressed over relationship records -- termed ownership-or-control statements before BODS 0.4 -- reachable from a declared subject entity. This profile is written against BODS 0.4. Taxonomic narrowing corresponds to reducing the depth of the ownership chain a predicate ranges over. A relying party's question is characteristically about ultimate beneficial ownership -- the transitive closure -- while a register may be able to answer only a bounded-depth predicate over direct or once-removed interests. The parent of a predicate at depth n is the corresponding predicate at depth n-1. The direct-interest predicate is the root of this profile's branch of the Predicate Taxonomy, and the walk of fails as projection-unsupported on reaching it, as it does at the taxonomy root. A Bilateral Register Agreement declaring arp-profile-bods MUST supply the maximum chain depth over which the register's permitted predicates are evaluated. Where the Canonical Claim ranges over the transitive closure and the register's declared maximum depth is finite, the projection is a narrowing and MUST be recorded in Narrowed-From. An implementation MUST NOT treat a bounded-depth no-match as a transitive-closure no-match. The rule is stated in and applies to that register's contribution, not to the Combined Verdict: a no-match returned at bounded depth against a closure claim is re-typed to indeterminate before aggregation, and the Verdict Arithmetic then proceeds unchanged. A match found at any depth does establish the existential closure predicate and is not re-typed. The depth at which the register answered is reported in the Applied-Parameter Set of its Partial Attestation and MUST be carried into the Projection Record of . A register MAY answer at a shallower depth than the declared maximum; the declared maximum is therefore not a substitute for the applied value, and re-typing under turns on the applied value. Interest thresholds -- the percentage at which an interest becomes reportable -- vary by jurisdiction and are properties of the register, not of the claim or of the format. A Bilateral Register Agreement declaring arp-profile-bods MUST supply the threshold its permitted predicates assume. Two registers answering the same predicate under different thresholds are not answering the same question. The reconciliation server MUST add register-threshold-divergence to the Server-Recorded Divergence-Axis Set wherever the Reconciliation Output combines registers whose declared thresholds differ, irrespective of the verdicts they returned. In this profile the ownership and control predicates are threshold-sensitive; the identity and existence predicates are not.

Corporate registries: vCard and the Organization Ontology A profile in this class MUST declare for any branch of its predicate space over which taxonomic narrowing is defined. expresses organisational hierarchy only within one organisation's own ORG structured value and defines no property relating one organisation to another, so a vCard-only profile has no term capable of satisfying the parent-relation requirement of and MUST NOT declare a narrowing branch. vCard remains available for the identifying and contact predicates, over which no narrowing is defined. For registers expressing legal-entity and organisational structure, a profile MAY declare vCard properties or classes and properties as the vocabulary in which permitted predicates are expressed. A profile MUST declare exactly one parent relation for each branch of its predicate space, and MUST partition that space so the branches do not overlap. Declaring two relations applicable to one predicate would make the taxonomic walk of reach two predicates at equal distance, which that section requires to fail as projection-ambiguous. Where is used, org:subOrganizationOf is the parent relation for the organisational-structure branch, and org:hasSite for the branch of predicates ranging over establishment or place of business. Neither vocabulary asserts the legal effect of a recorded fact. does carry a notion of legal recognition -- org:FormalOrganization denotes an organisation recognised in legal jurisdictions, and org:identifier a company registration number -- but recognition is not determination. A predicate expressed in these terms is a predicate about a register's recorded representation of an entity, not about the entity's status in law, and a profile MUST NOT be read as asserting the latter. The vocabulary is pinned to as at its 2014 Recommendation and to . A Bilateral Register Agreement declaring this profile supplies the register's jurisdiction identifier and the identifier scheme of its org:identifier values. No predicate in this profile is threshold-sensitive: corporate registries record recognition rather than a quantified interest.

Customs and transport: UN/CEFACT and the WCO Data Model For customs declarations and transport registers, a profile MAY declare core components or classes as the vocabulary for permitted predicates. Both express declaration-side and authority-side facts, and telling them apart is the purpose of this profile rather than a property of the vocabularies. The WCO Data Model's Declaration Response and its Licence, Permit, Certificate and Other packages record authority determinations, as does UN/CEFACT's eCERT for sanitary and phytosanitary certification; the goods and cargo declaration classes in both record what was declared to an authority. A Bilateral Register Agreement declaring arp-profile-customs-wco MUST supply, for each permitted predicate, whether it ranges over a declared fact or over a determined one. Where a relying party's Canonical Claim ranges over a determined fact and the register can answer only over a declared one, that is a narrowing and MUST be recorded in Narrowed-From. The reconciliation server MUST derive the Divergence Axis declared-not-determined from the Narrowed-From field and add it to the Server-Recorded Divergence-Axis Set of whenever the narrowing occurred, whether or not it changed the Combined Verdict; the corresponding contribution is re-typed under . The register cannot record it: the register never sees the Canonical Claim, and the Combined Verdict does not exist until every Partial Attestation has been received. The vocabulary is pinned to Version 4 of the and to the UN/CEFACT Core Component Library release the Bilateral Register Agreement names, which it MUST name. The Agreement also supplies the declaration types the register answers over. No predicate in this profile is threshold-sensitive.

Sanctions: consolidated list formats For registers expressing designation status by reference to a consolidated list -- , or equivalent -- the permitted-predicate set is expressed over designation of a subject entity on a named list. Consolidated lists are republished on no fixed schedule -- OFAC states there is no predetermined timetable, and the EU list is updated as amending regulations are adopted -- and are distributed either as full republications or as delta updates against a prior state. That the cadence is event-driven strengthens the requirement below rather than weakening it: a relying party cannot infer list state from the clock. A designation verdict is meaningful only relative to the list state that produced it, and this has a consequence the rest of this document depends on: without it, a change in a historical Combined Verdict cannot be attributed to a policy change rather than to a list change. Accordingly the requirements of apply. A Bilateral Register Agreement declaring arp-profile-sanctions-consolidated MUST supply the set of lists the register consults and, for each, the identifier by which the register expresses that list's state. Where the register publishes both a full list and deltas, the identifier MUST denote the resulting state and not the delta applied to reach it. A profile in this class names no single vocabulary, consolidated sanctions lists having no common schema. It instead pins, per register, the list identifier and the publisher's state-identifier form that requires, both supplied by the Bilateral Register Agreement, together with the matching predicate set the register answers over. No predicate in this profile is threshold-sensitive: a designation is a listed-or-not fact.

Source-Data Version Binding Where a register's answer depends on a source data state that changes independently of the Bilateral Register Agreement and of the Policy Version -- a consolidated sanctions list being the characteristic case -- the Partial Attestation MUST carry a Source-Data Version Identifier Set: one identifier for each source consulted in evaluating the Projected Predicate. Each identifier is a two-element CBOR array of the list name as declared in the Bilateral Register Agreement, as a text string, and the state identifier the LIST PUBLISHER assigns to that state, rather than any value of the register's own devising. The state identifier is itself a two-element CBOR array of a form discriminator and a value. The discriminator is the text string token where the publisher assigns a version token, and the value is that token as a text string exactly as the publisher renders it, with no normalisation, trimming or case folding. The discriminator is the text string digest where the publisher assigns none, and the value is the SHA-256 digest, as a 32-octet CBOR byte string, of the octets the publisher serves for that state, taken as served and before any decompression, transcoding or reformatting the register applies. The discriminator is present because the two branches are a text string and a byte string in one position, and a reader that must infer which it holds from the CBOR major type is a reader that will be wrong the first time a publisher issues a token that happens to decode. The "as served, before decompression" rule is present because a consolidated list published as a compressed archive has at least two byte sequences with an equal claim to being the corpus, and two registers that choose differently produce two identifiers for one state, which would then read as a version change that never occurred. The Source-Data Version Identifier Set MUST be encoded as a CBOR array sorted in bytewise lexicographic order of the deterministic CBOR encoding of each member. Every other set this document carries into a signature is ordered, and for the reason gives: an unordered set gives one signed artefact as many digests as it has permutations. A register consulting three lists would otherwise have six conforming encodings of one attestation, each producing a different Merkle leaf under and a different Reconciliation Hash. A register-chosen opaque string would be an arbitrary-bandwidth channel from register to relying party, carried under signature into a sealed and ledgered artefact, and the rule that differing identifiers MUST NOT be read as disagreement would normalise it. The reconciliation server MUST reject an identifier that is not drawn from the publisher's own state sequence, under with the reason attestation-source-version-invalid. The tuple form is what keeps identifiers issued by one register over different lists from colliding, so that a register consulting several lists can denote the state of each. The Source-Data Version Identifier Set MUST be carried in the arp-source-data-version COSE header parameter of the Partial Attestation's protected header, and is thereby covered by the Partial-Attestation signature. It MUST be carried into the Per-Register Result Set of for each addressed register that supplied one, and is thereby covered by the Sealing Signature. A register MUST evaluate every Projected Predicate over a given list against the state the corresponding member of its declared Source-Data Version Identifier Set denotes, and MUST use the same identifier for every Partial Attestation it issues over that list until it adopts a new state. Without this the identifier would vary per subject and become a disclosure channel. Given that requirement this does not weaken minimum disclosure: a list-state identifier is a property of a published corpus rather than a register record, it discloses which published state was consulted and nothing about the subject entity, and it is identical across every Partial Attestation the register issues over that list regardless of verdict. Retroactive Evaluation depends on this. On re-evaluation under an updated Pattern Library or Policy Version, an implementation MUST distinguish a material change in a historical Combined Verdict arising from the change in policy state from one arising from a change in Source-Data Version. Both MUST trigger Sovereign Re-Notification where material, and the notification MUST state which of the two occurred. Where an implementation cannot distinguish them, it MUST emit a Post-Seal Evaluation Record carrying attribution-indeterminate per rather than attribute the change to policy. An implementation MUST NOT infer that two Partial Attestations whose Source-Data Version Identifier Sets differ for a list they have in common disagree. They may be answers to the same predicate against different states of the same corpus. The reconciliation server MUST record this as source-version-skew, which is distinct from freshness-stale: a skewed attestation is within its freshness window and is retained and combined, whereas a stale one falls outside that window and is rejected under .

Per-Register Encryption These are requirements on whatever bilateral channel leaves each Bilateral Register Agreement to declare; they are properties the channel MUST provide and not a wire construction this document pins. Each Per-Register Claim Projection MUST be encrypted under the addressed register's public key material declared in the Bilateral Register Agreement. The Reconciliation Nonce MUST be transmitted in the clear alongside the ciphertext, and the encryption operation MUST bind the Bilateral-Register-Agreement Hash and that nonce into the ciphertext as authenticated additional data, such that a register attempting to decrypt under a stale Bilateral-Register-Agreement Hash, or with a nonce other than the one the ciphertext was sealed against, fails at the authenticated-additional-data verification step. The register MUST verify that the nonce so bound equals the Reconciliation Nonce field of the decrypted projection. The nonce travels in the clear because authenticated additional data is an input to the decryption operation and cannot be recovered from the plaintext that operation produces. It discloses nothing: it is a random value carrying no information about the subject or the claim. These two are the only values so bound. Authenticated additional data detects a mismatch only against an expectation the receiver independently holds. A register independently holds its own agreement, and it is handed the nonce. It does not hold the Pattern-Library Version Identifier: the Pattern Library is the reconciliation server's internal adversarial-test corpus and is not published to registers, so binding it would either fail universally or be supplied alongside the ciphertext by the same party that chose it, detecting nothing. A register MUST NOT issue more than one Partial Attestation for a given Reconciliation Nonce, and MUST reject a projection whose nonce it has already answered. Without this a captured ciphertext could be replayed indefinitely, each replay yielding a freshly timestamped signed attestation and defeating the freshness window of .

Partial Attestation Reception A Partial Attestation comprises:

• Register Identifier
• Reconciliation-Verdict Field (match, no-match, partial-match, or indeterminate)
• OPTIONAL Divergence-Axis Field
• Bilateral-Register-Agreement Hash
• Policy-Version Hash
• OPTIONAL Source-Data Version Identifier Set, present where required by and carried in the arp-source-data-version COSE header parameter of
• OPTIONAL Applied-Parameter Set, being the profile parameters the register actually applied in evaluating the Projected Predicate, present wherever the Profile Parameter Set of the Per-Register Claim Projection was non-empty
• Query Binding, the SHA-256 digest over the deterministically encoded CBOR array ["arp-query-binding-v1", Reconciliation Identifier, Projected Predicate, Subject Reference, Reconciliation Nonce], those four values taken from the Per-Register Claim Projection it answers. The construction is a five-element array whose first element is a fixed domain-separation string, rather than a byte concatenation, so that two implementations cannot differ on framing and the digest cannot collide with any other construction in this document. Within that array the Reconciliation Identifier is a byte string of 80 octets as fixes it, the Projected Predicate is a text string, the Reconciliation Nonce is a byte string of at least 16 octets, and the Subject Reference takes the CBOR type the Subject Reference form of item 8 of declares, which that Agreement MUST state. The register and the reconciliation server compute this digest independently and MUST obtain the same value, so an element whose type is left open is an element on which they can differ while agreeing on every negotiated term
• Freshness Timestamp
• Cryptographic Signature, a COSE_Sign1 by the register whose payload is the CBOR array of the fields above in the order listed, with an absent OPTIONAL or conditionally absent field encoded as CBOR null so that position is preserved, encoded under Section 4.2.1 of . The register's signing key is published in its key set under , so that a relying party or auditor holding the attestation can resolve the key and verify the signature without the reconciliation server's assurance

The Query Binding is what makes an attestation an answer to a question rather than a free-standing assertion. Without it the signed payload says only that a register returned a verdict under some agreement and policy version at some time, and says nothing about what it was asked. Two consequences follow, and both are severe: an attestation harvested for one subject could be placed into the Per-Register Result Set of a reconciliation about another subject and would verify against every other check; and a register could answer the same question differently to two requesters and deny having done so, because its signature would not identify the question. The arp-policy-version-hash, arp-bilateral-agreement-hash and arp-source-data-version in a Partial Attestation's protected header MUST equal the corresponding payload fields, and an implementation MUST reject an attestation where they differ: a value carried twice with no equality rule is a value an implementation may read either way. The third is included because carries the Source-Data Version Identifier Set in the protected header and again into the Per-Register Result Set, which is the condition this rule exists to govern, and an earlier revision applied the rule to the first two only. The reconciliation server MUST recompute the Query Binding from the projection it transmitted and MUST reject an attestation whose Query Binding does not match, under with the reason attestation-binding-mismatch. The Query Binding Record of carries the three projection values and the register's signed attestation into the Output, so that a relying party or auditor can recompute the binding and verify the register's signature independently. A check performed only by the reconciliation server would rest on the honesty of the party the rest of this document declines to trust. The Reconciliation Nonce is unique per Per-Register Claim Projection per and MUST NOT be reused, so that an attestation is admissible only into the reconciliation, and against the register, that elicited it. The Partial Attestation payload SHALL NOT contain any register-record field, any pre-image of the register record, or any field beyond those enumerated. Restricting the Partial-Attestation payload to the enumerated fields, of which the verdict, the divergence axis, the applied parameters and the Query Binding -- a digest over the Subject Reference -- vary with the subject, is the mechanism by which ARP limits raw-record disclosure. Residual inference channels are discussed in .

Merkle Construction Two structures in this document commit to a set of digests through a Merkle tree: the Merkle Root of Hash-Linkage Aggregation, and the Examined-Set Root of . Both use this construction, so that an inclusion proof produced by one implementation verifies under another. Leaves are the digests to be committed, sorted in bytewise lexicographic order and deduplicated. Deduplication is why an Examined-Set Root commits to distinct Claim Hashes and the count beside it counts Reconciliation Outputs: two Outputs over one claim share a Claim Hash, so the leaf count and the examined count need not be equal and neither is derivable from the other. A leaf node is SHA-256(0x00 || leaf). An internal node is SHA-256(0x01 || left || right). Where a level has an odd number of nodes, the last is carried up to the next level unchanged rather than duplicated. A tree over one leaf has that leaf's leaf-node hash as its root; a tree over no leaves has thirty-two zero octets as its root. For every non-empty tree this is the Merkle Tree Hash of Section 2.1.1 of instantiated with SHA-256. carries the hash algorithm as a log parameter and this document fixes SHA-256, which is the hash that Certificate Transparency logs built on the earlier specification also use, so an implementer arriving from either computes the same tree. The odd-node rule stated above and that recursive split at the largest power of two below the leaf count are two descriptions of one tree: at every leaf count they produce the same root, and at every leaf count and index they produce the same sibling array. An implementation may compute either way and interoperate with one that computes the other. This is stated because the two rules do not look alike, so a reader who knows Certificate Transparency has no way to establish from the prose alone that they agree; and because a third convention is in common use, in which the last node at an odd level is duplicated and paired with itself. That convention produces the same root at every leaf count that is a power of two, because no level of such a tree is ever odd, and a different root at every other leaf count. A conformance vector taken at four or eight leaves will therefore not detect it, and an implementation that ports it will pass a test suite and diverge in production. This document and Certificate Transparency diverge at exactly one input to the tree function, the empty tree, and the divergence is deliberate. Certificate Transparency defines the Merkle Tree Hash of the empty list as the hash of the empty string, which under SHA-256 is e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855; this document defines it as thirty-two zero octets. The Certificate Transparency value is a well formed digest that a verifier reproduces successfully and may then treat as a root that commits to something. Thirty-two zero octets is a value no commitment in this document produces, so it cannot be mistaken for one. An implementation MUST use the value defined in this section and MUST NOT substitute the Certificate Transparency empty-tree value. The requirement below, that a verifier reject any inclusion proof presented against the empty root, applies to whichever value a construction gives the empty tree, and the reason for it does not depend on which value that is. Two further differences are matters of input and of encoding rather than of the tree, and each is a place an implementation ported from a Certificate Transparency log will be wrong if it is carried over unchanged. This document sorts leaves in bytewise lexicographic order and deduplicates them before the tree is built, where a Certificate Transparency log commits to entries in the order it received them; an implementation MUST apply the ordering and deduplication stated above and MUST NOT assume submission order. And this document's inclusion proof carries the leaf alongside the index, the leaf count and the sibling array, where the inclusion proof of Section 2.1.3 of carries the index and the tree size but not the leaf, which its verifier is assumed already to hold. The leaf is the only field that differs, and states what a verifier must do with it. An inclusion proof is a CBOR array of the leaf, its zero-based index, the leaf count, and the array of sibling hashes from the leaf's level upward. Domain separation between leaf and internal nodes is what stops a proof of an internal node being presented as a proof of a leaf. Three properties of that array are stated here because each is a place two implementations otherwise diverge while both believing they conform. The array carries one entry for each level at which the node being proved has a sibling, and no entry for a level at which it was carried up unchanged, so its length is not in general the base-two logarithm of the leaf count and a verifier MUST NOT derive the expected length that way. No direction bit is carried: at each level the verifier derives whether the sibling is the left or the right operand from the index and the leaf count, taking the floor of half the index and the ceiling of half the level width as it ascends. Halving the width by truncation instead gives the wrong width at every leaf count that is not a power of two -- five leaves give widths 5, 3, 2, 1 and not 5, 2, 1 -- which is precisely the range of leaf counts this section exists to pin down. The derivation is well defined because the shape of the tree is fixed by the leaf count alone. And the empty tree's root of thirty-two zero octets admits no inclusion proof; a verifier MUST reject any proof presented against it rather than treat a root it can reproduce as a root that commits to something.

Leaf binding The leaf a proof carries is a convenience and is not evidence. A verifier MUST compute the leaf from the object whose inclusion is being proved -- the Signing Input Digest of the Partial Attestation for a Merkle Root under , the Claim Hash for an Examined-Set Root under -- and MUST use that computed value, and no value taken from the proof, as the input to the sibling walk. Where the proof carries a leaf, the verifier MUST refuse the proof if the computed value does not equal it, and MUST perform that comparison before the sibling array is walked. The requirement is stated over the object rather than over the carried field because the field is not always present. permits per-register inclusion proofs to be encoded as COSE Receipts , whose inclusion proof carries no leaf; a requirement written only as a comparison against a carried leaf would be vacuous under that encoding, which is the encoding a SCITT-aware verifier is most likely to use. The ordering is the whole of the requirement. A proof whose leaf is lifted unchanged from another object's valid proof folds to the correct root under a sibling array that verifies, because it is a correct proof -- of the other object. A verifier that walks the path first and takes the carried leaf on trust accepts it, and concludes that the object it holds was committed when what was committed was something else. Nothing in the walk depends on the object, so the walk cannot detect this; only the recomputation can. It is the more dangerous half of its pair: a malformed proof fails loudly on every path a verifier tries, while a valid proof bound to the wrong leaf passes every check except this one.

Verification outcomes The preceding rules tell a verifier to refuse. They do not give it any way to record which refusal it made, and four conditions that arrive at "refuse" through this section are evidence about four different things. A deployment that reports them alike reports something that did not happen, and the report will be believed, because the check that produced it worked exactly as specified. A verifier that refuses a proof or an artefact under this document MUST record a Verification Outcome, drawn from the registry of , and MUST NOT report one as another. The initial values are:

proof-against-empty-root:

A proof was presented against the empty-tree root of . Evidence of neither equivocation nor re-encoding: the empty root commits to nothing and no proof against it can be valid.

leaf-object-mismatch:

The leaf recomputed from the object differs from the leaf the proof carries. Evidence of equivocation by the serving party, and the case this section exists to catch.

root-mismatch:

The sibling walk completed and produced a root other than the one named. Evidence of equivocation by the serving party.

same-act-distinct-encodings:

The artefact the verifier holds and the artefact the proof or digest commits to have equal Signing Input Digests and unequal enveloped bytes. Evidence of a re-encoding and not of equivocation. A verifier MUST test for this condition before reporting leaf-object-mismatch or root-mismatch, and where it holds, MUST report this outcome instead.

The last is the one that changes what a reader concludes. Two artefacts with one Signing Input Digest are one signing act under two encodings, which shows a third party holding no key can produce from the honest signer's own bytes -- and which, for ECDSA, is produced by any implementation that normalises s on ingest while believing it is hardening. Reporting that as detected tampering accuses a party of equivocating on the strength of an operation an intermediary performed correctly. The constructions of make the digests stable; this makes the report that survives them accurate.

Aggregation The aggregation subsystem operates in Hash-Linkage Aggregation. Each Partial Attestation is committed to a Merkle tree as defines it, under the leaf value that is its Signing Input Digest, and the resulting Merkle Root is carried in the Reconciliation Output. The leaf is the Signing Input Digest and not a digest of the attestation as received, so that the leaf a verifier computes under does not depend on which of several byte-strings carrying one register signature it happens to hold. Its per-register inclusion proofs MAY be encoded as COSE Receipts , enabling any SCITT-aware verifier to check inclusion without a bespoke proof format. Each leaf commits one register's attestation individually, so an inclusion proof discloses no other register's payload.

Registers That Do Not Answer A register may fail to produce a usable Partial Attestation. Every such state has a defined outcome, because dropping the register silently would produce exactly the addressed-register-cherry-picking pattern the Adversarial Pre-Transmission Test exists to detect. The Per-Register Result Set MUST carry an entry for every addressed register. Where no usable attestation was received, the entry carries no Attested Verdict and carries instead, in its own field, a Non-Answer Reason drawn from:

• projection-ambiguous and projection-unsupported, where the projection itself failed and no projection was transmitted
• agreement-drift-suspended, where reconciliation against that register was suspended for Bilateral-Register-Agreement drift
• attestation-stale, where the Freshness Timestamp fell outside the declared window and the attestation was rejected
• attestation-signature-invalid, where the signature did not verify
• attestation-echo-mismatch, where a value the register echoed did not match the one sent, or a value carried in the protected header did not equal the corresponding payload field
• attestation-binding-mismatch, where the Query Binding the server recomputed did not match the one the attestation carries, which is an attestation elicited for a different question
• attestation-source-version-invalid, where a Source-Data Version Identifier was not drawn from the publisher's own state sequence
• attestation-scope-exceeded, where the register attested a Divergence Axis the registry of records as server-recorded
• register-unresponsive, where no attestation was received within the window declared in the Bilateral Register Agreement
• register-refused, where the register declined to answer, whether under its own statutory access regime or under the Agent-IFF policy
• query-budget-exhausted, where the reconciliation would exceed the per-principal per-subject query budget declared under
• subject-ceiling-exhausted, where the reconciliation would exceed a per-subject ceiling declared under
• audience-constraint-exceeded, where the requested Audience Set exceeds the audience constraint that register declares under
• non-answer-unattested, where the register asserted a register-attested reason without a verifying Non-Answer Statement

Each Non-Answer Reason is either register-attested or server-observed, and the registry of MUST record which for every registration. register-refused is register-attested. attestation-stale and the five attestation- reasons above are server-observed but arise from an attestation the server holds. The remainder are server-observed with no register artefact behind them. Earlier revisions carried a single attestation-unverifiable covering all five of those conditions, and normative text in four other sections directed implementations to it for causes its own definition did not name. They are not variants of one condition and an auditor cannot be asked to treat them as one. A failed signature is a broken or impersonated register. An echo mismatch is an attestation about a different policy state. A binding mismatch is the reconciliation server presenting an attestation elicited for a different subject or predicate, which is a server-side attack and not a register fault at all. A source-version invalidity is a register attempting a covert channel. A scope excess is a register claiming competence the registry says it does not have. Recording all five as one value tells the Register Operator reading its own entry under that something was wrong with its attestation, and does not tell it whether the fault was its own. This document made exactly this argument for non-answer-unattested two paragraphs below and did not apply it here. An implementation MUST NOT record any of the five under a value that does not name its cause. Where a Non-Answer Reason is register-attested, the Per-Register Result Set entry MUST carry a Non-Answer Statement in the field defines for it. The Statement is a COSE_Sign1 by that register, under the primitive its Bilateral Register Agreement declares and under a key resolvable as in , whose payload is the CBOR array ["arp-non-answer-v1", Reconciliation Identifier, Projected Predicate, Subject Reference, Reconciliation Nonce, Non-Answer Reason] encoded under Section 4.2.1 of . The Reconciliation Identifier is inside the payload for the reason the Query Binding of carries it: without it a refusal elicited in one reconciliation is admissible as a refusal in another over the same subject and predicate. Where a register-attested reason is recorded without a Statement, or with one that does not verify, the reason MUST be replaced by non-answer-unattested. That is a distinct reason and not any of the attestation- reasons, which denote a Partial Attestation the server holds and could not verify; collapsing the two would put the missing-refusal case back into a server-observed bucket and undo the distinction this rule exists to draw. Without that rule a register-refused is an unattested assertion by the party that transmitted the projection, and a server can suppress a match by claiming the register declined. The server can still downgrade a reconciliation to indeterminate by asserting a server-observed reason -- register-unresponsive is indistinguishable from a network failure by construction, and this document does not pretend otherwise -- but it cannot dress suppression as an act of the register. Suppressing a sanctions hit is the harm this domain cares about, and the difference between "the register would not say" and "I did not ask" is the difference the record must preserve. A Non-Answer Reason is not a verdict, occupies its own field of the Per-Register Result Set per , and MUST NOT be combined by the Verdict Arithmetic. Its effect is given in : a reconciliation with any non-answering register cannot reach a decisive Combined Verdict. Where the reason is attestation-stale, freshness-stale MUST also be added to the Server-Recorded Divergence-Axis Set against that Register Identifier. A reconciliation server MUST reject a Partial Attestation that attests a Divergence Axis the registry of records as server-recorded, with the reason attestation-scope-exceeded. A register cannot attest a relation between itself and another register, which is what those axes are.

Verdict Re-Typing A register answers the Projected Predicate it was sent, which may be a narrowing of the Canonical Claim Predicate. Where the narrowing means the register's answer does not bear on the claim as asked, the reconciliation server MUST re-type that register's Reconciliation-Verdict Field before aggregation, and MUST record the attested value, the re-typed value and the ground on which it re-typed in the Per-Register Result Set, so that an auditor can reproduce the decision without the server's assurance. Re-typing is confined to these cases:

• Any contribution other than match, attested against a bounded-depth predicate where the Canonical Claim ranged over a transitive closure, is re-typed to indeterminate. A bounded-depth answer that is not a match is evidence about the bounded depth only, and that is as true of partial-match and indeterminate as of no-match. A match is not re-typed: an interest found at any depth establishes the existential closure predicate.
• A match or no-match attested over a declared fact, where the Canonical Claim ranged over a determined fact, is re-typed to partial-match under an operator that admits that value and to indeterminate under one that does not, per .
• A contribution from a register whose declared interest threshold differs from that of any other addressed register, where the Canonical Claim's predicate is threshold-sensitive, is re-typed to partial-match under an operator that admits that value and to indeterminate under one that does not. Two registers answering under different thresholds are not answering the same question, and annotating that on the Reconciliation Output while allowing a decisive Combined Verdict to be built from it would state a conclusion the inputs do not support. Threshold-sensitivity is a property of a Register Data-Format Profile, which declares which of its predicates are threshold-sensitive, and the test above names the Canonical Claim Predicate, which is not expressed in any profile. The test is therefore evaluated as follows, and is defined over a register set whose members declare different profiles. The Canonical Claim Predicate is threshold-sensitive where the Per-Register Claim Projection transmitted to ANY addressed register was a predicate that register's declared profile marks threshold-sensitive. Taking the disjunction rather than requiring agreement is deliberate: a mixed-profile register set in which one profile marks the predicate threshold-sensitive and another is silent is precisely the set in which the thresholds may differ unnoticed, and requiring every profile to mark it would disable the test in the case it exists for.
• A match attested against a Projected Predicate that is a proper ancestor of the Canonical Claim Predicate is re-typed to partial-match under an operator that admits that value and to indeterminate under one that does not, under the ground projection-broadened. The projection function of resolves by taxonomic prefix match upward, producing the nearest permitted ancestor, so a register answering a Projected Predicate that narrowing did not reach is answering a broader question than the claim asked. A subject designated on some US sanctions list is not thereby designated on the OFAC SDN list, and a decisive match assembled from the ancestor states a conclusion the input does not support. A contribution other than match is not re-typed on this ground: a no-match over an ancestor entails no-match over every descendant of it, so the broadening is harmless in that direction and re-typing it would discard sound evidence. Earlier revisions covered the converse only. The opening sentence of this section says a register answers a Projected Predicate "which may be a narrowing of the Canonical Claim Predicate", and the projection function produces an ancestor, which is the opposite relation. The Output records the broadening in the Narrowed-From field of the Projection Record, so a relying party inspecting it could see what happened; nothing obliged it to look, and the Combined Verdict was decisive either way. Recording a divergence while permitting a decisive verdict built on it is the failure ground 3 above is written against, and it applied here and was not applied. The Divergence Axis claim-projection-narrowed-beyond-attestation-scope names this condition and is register-attestable, optional in the attestation, and connected to no normative rule anywhere in this document; it appears in its own enumeration and nowhere else. An axis a register need never emit, and which changes no verdict when emitted, is not a control. This ground is.

Re-typing operates on a register's contribution. It does not override the Verdict Arithmetic resolved under , which is applied afterwards to the re-typed set and is otherwise unaffected. An implementation MUST NOT re-type on any ground not enumerated here.

Verdict Arithmetic The Verdict Arithmetic combines the Reconciliation-Verdict Fields of the Per-Register Result Set, after any re-typing under , into the Combined Verdict. The requester names the applicable regimes in its Canonical Claim; it does not choose the operator. The operator and every parameter it takes are resolved by the reconciliation server from the policy-epoch store of , keyed on the predicate and the named regimes, and are committed to the Policy-Version Hash. They are carried into the Reconciliation Output so that a relying party can reproduce the combination. A requester able to choose both the operator and its threshold could choose the verdict: disjunction over five registers and threshold-count with a threshold of five differ only in which answer they return over the same contributions, and selecting between them after seeing which registers were addressed is verdict shopping that no downstream check would detect. Naming a regime is a claim about which law applies, which the requester is competent to make and accountable for; selecting an operator is a determination about how evidence combines, which the deployment's policy makes. Naming regimes is not thereby unconstrained. The reconciliation server MUST verify that every regime the Applicable-Regimes Set names is one the policy-epoch store admits for that predicate, and MUST refuse a claim naming a regime that is not, returning a Remediation Advisory identifying it. Without that check a requester enumerates admissible regime sets, reads out of the Outputs it receives which operator, threshold and reliance interval each resolves to, and selects the combination that returns the answer it wants -- taking the longest reliance interval with it. That is verdict shopping at one remove. There is nothing to probe for: requires the server to publish the resolved operator, its parameters and the reliance interval per predicate and regime set, so the mapping is available without probing and the admitted-regime check is what constrains the choice. Three rules apply to every operator and take precedence over the operator's own table:

• The Addressed-Registers Identifier Set MUST NOT be empty, and a Combined Verdict MUST NOT be computed over an empty contribution set. Every operator below is defined by a condition universally quantified over the contributions, so every one of them is vacuously satisfied where there are none: conjunction yields match, disjunction and threshold-count yield no-match, and the two rules that follow -- both of which begin "where any" -- do not fire, because there is no contribution to be indecisive. A decisive verdict from no evidence at all is the failure mode the rest of this section is built to prevent, and it is reached not by an operator behaving badly but by every guard being true of nothing. A relying party MUST reject an Output whose Addressed-Registers Identifier Set is empty, and MUST NOT treat its Combined Verdict as a verdict.
• Where any addressed register has no decisive contribution because it did not answer, was refused or was rejected under , the Combined Verdict MUST be indeterminate. An operator MUST NOT reach a decisive verdict over an incomplete register set, which would be indistinguishable from addressed-register-cherry-picking.
• Where any contribution is indeterminate, the Combined Verdict MUST be indeterminate wherever the operator's table would otherwise yield no-match. An indeterminate contribution is an absence of evidence and a decisive negative may not be built on one, so the rule states the substitute result rather than only a prohibition; a prohibition without a substitute would leave the verdict undefined in exactly the cases it governs.

Operators are drawn from the registry of . Subject to those rules, the initial four are:

conjunction:

match where every contribution is match. no-match where any contribution is no-match. partial-match where every contribution is match or partial-match and at least one is partial-match. indeterminate otherwise.

disjunction:

match where any contribution is match. no-match where every contribution is no-match. partial-match where at least one is partial-match and none is match. indeterminate otherwise.

threshold-count:

match where the count of match contributions meets or exceeds the threshold resolved for the named regimes. no-match where the count of match contributions cannot reach the threshold and no contribution is indeterminate. indeterminate otherwise, which includes every case in which an indeterminate contribution is present and the threshold is not met. partial-match contributions do not count toward the threshold.

source-class-quorum:

threshold-count evaluated per source class, over the partition and the per-class threshold resolved for the named regimes, then combined across classes by conjunction. A source class containing no addressed register contributes indeterminate and MUST NOT contribute no-match. Without that rule the class is threshold-count over nothing: the count of match contributions cannot reach a threshold of one or more, no contribution is indeterminate because there is no contribution, and the class yields a decisive negative built on an empty class -- which conjunction then propagates to the Combined Verdict. The indeterminate-substitution rule above does not reach it, because that rule governs evidence that is present and inconclusive and this is evidence that is absent. Suppressing a hit by partitioning it into a class with no members in it is a decisive negative assembled out of the partition, and the partition is resolved from the policy-epoch store rather than from the registers actually addressed.

Every operator admits partial-match except threshold-count and source-class-quorum, which do not. Where would re-type a contribution to partial-match under an operator that does not admit it, the contribution is re-typed to indeterminate instead.

Reconciliation Output A Reconciliation Output comprises:

• Reconciliation Event Identifier
• Reconciliation Identifier
• Claim Hash
• Reconciliation Timestamp
• Reliance Horizon of
• Audience Set of
• Combined Verdict
• Verdict Arithmetic as resolved under , together with every parameter that operator takes -- the threshold for threshold-count, and both the source-class partition and the per-class threshold for source-class-quorum
• Addressed-Registers Identifier Set, each member an Authority Origin, sorted in bytewise lexicographic order of its UTF-8 encoding
• Bilateral-Register-Agreement Hash Set, sorted in bytewise lexicographic order of the digests themselves, in the order of the Addressed-Registers Identifier Set having no meaning once a register may be absent from a set
• Policy-Version Hash
• Pattern-Library Version Identifier
• Requester-Binding Class
• Per-Register Result Set, one entry per addressed register, ordered by Register Identifier in bytewise lexicographic order of its UTF-8 encoding
• Aggregation-Method Descriptor, drawn from the registry of
• Merkle Root, constructed as in
• Server-Recorded Divergence-Axis Set, possibly empty
• OPTIONAL Override Record, present exactly where an Adversarial Pre-Transmission Test failure was overridden
• Sealing-Key Identifier
• Sealing Signature, a COSE_Sign1 by the reconciliation-server sealing key whose payload is the CBOR array of this Output with the Sealing Signature position alone encoded as CBOR null, so that it covers every other field including the Sealing-Key Identifier

The Reconciliation Event Identifier is a 16-octet value drawn from a cryptographically secure random source at the start of a reconciliation, unique to that reconciliation across the life of the deployment. The Reconciliation Identifier is the Claim Hash concatenated with the Policy-Version Hash concatenated with the Reconciliation Event Identifier. Earlier revisions omitted the third component, and the first two are both reproducible functions of enumerated inputs. Two reconciliations over one claim under one policy state therefore shared an identifier, and the protocol keys three mechanisms on it that each assume it names one event:

• A register's own read under is keyed on the Reconciliation Identifier, and exists so that a server cannot discard a register's signed match and record register-unresponsive while the only party holding the contradicting artefact has no operation with which to produce it. Where two reconciliations shared the identifier, a server could record the register's match in the first and suppress it in the second, and serve the first to the register's audit read. The register sees its answer faithfully recorded and the suppression is invisible.
• The Query Binding of carries the Reconciliation Identifier so that an attestation is admissible only into the reconciliation that elicited it. Every element of that preimage was identical across the two, so an attestation elicited in the first verified unchanged inside the second.
• The Non-Answer Statement carries it so that a refusal elicited in one reconciliation is not admissible as a refusal in another over the same subject and predicate -- which, under unchanged policy, is precisely when the identifier repeated.

The three protections were each written against the same assumption and the assumption was not established anywhere. A retroactive supersession under a Source-Data Version trigger leaves the policy state unchanged by definition, so the identifier repeated on the path the document itself constructs, not only on one a requester might contrive. The Event Identifier is what the three mechanisms were already relying on. It is carried in the Output as its own field, so it is inside the Reconciliation Hash preimage: two reconciliations that address no register and are sealed in the same second would otherwise produce one Reconciliation Hash, which is the ledger index and the retrieval key, and no field distinguishing them. The Event Identifier is not a secret and carries no requester-supplied content. It is random rather than a counter so that it discloses nothing about reconciliation volume to a register or to a relying party, and 16 octets rather than 32 because it needs only uniqueness within a deployment. The Claim Hash binds the Output to the question it answers. Without it a relying party receives a Combined Verdict with nothing to attribute it to, and the Retroactive Evaluation Subsystem has no key to select on. The Verdict Arithmetic and its parameters are carried because a relying party cannot otherwise reproduce the combination from the Per-Register Result Set, and because turns on which values the operator admits. The Applicable-Regimes Set is a Canonical Claim field and is not itself carried in the Output, so naming the operator without its parameters would leave threshold-count and source-class-quorum irreproducible. source-class-quorum is threshold-count evaluated per class and therefore takes a threshold as well as a partition; carrying the partition alone would leave it as irreproducible as carrying neither, which an earlier revision did. Each entry of the Per-Register Result Set comprises:

• Register Identifier
• Answer State, either answered or not-answered
• Attested Verdict, present exactly where the Answer State is answered
• Non-Answer Reason of , present exactly where the Answer State is not-answered
• Effective Verdict, present exactly where the Answer State is answered, being the Attested Verdict or its re-typing under
• Re-Typing Ground, drawn from the registry of , present exactly where the Attested and Effective Verdicts differ
• Policy-Version Hash as echoed by that register, present exactly where the Answer State is answered
• OPTIONAL Divergence-Axis Field, as attested by that register
• OPTIONAL Source-Data Version Identifier Set, as attested by that register
• Projection Record, comprising the Narrowed-From field of the Per-Register Claim Projection where a projection was transmitted, the Applied-Parameter Set the register reported where the Answer State is answered, and the Subject Mapping Record of ; required wherever a projection was transmitted and either the projection narrowed or the Profile Parameter Set was non-empty
• Query Binding Record, present exactly where the Answer State is answered, comprising the Projected Predicate, the Subject Reference and the Reconciliation Nonce the server transmitted, and the register's signed Partial Attestation
• Non-Answer Statement, present exactly where the Answer State is not-answered and the Non-Answer Reason is register-attested under , comprising the Projected Predicate, the Subject Reference and the Reconciliation Nonce the server transmitted, and the register's signature over them together with the reason and the Reconciliation Identifier, as constructs it. The three projection values are carried here as well as in the Query Binding Record because the two are never both present and a verifier of either needs the preimage in the artefact it holds.

Each member of the Server-Recorded Divergence-Axis Set is a two-element array of a Divergence Axis and the Register Identifier it concerns, the second element being CBOR null where the axis concerns the reconciliation as a whole. Members are sorted in bytewise lexicographic order of that encoding. A uniform two-element member with an explicit null, rather than a member that is sometimes a pair and sometimes a scalar, is what makes the Set's contribution to the Reconciliation Hash determinate. Of the axes recorded by the server, freshness-stale and declared-not-determined are per-register and MUST carry a Register Identifier. source-version-skew is a relation between two or more registers, and one member MUST be added for each register involved, so that the set is a determinate function of the inputs rather than a choice between them; register-threshold-divergence concerns the reconciliation and MUST NOT. agent-action-scope-divergence is likewise a relation, between two capsules rather than between two registers, and one member MUST be added for each Register Identifier whose contribution the divergence concerns, or a single member carrying null where it concerns no register's contribution; the rule is stated for all five axes and not four because the Set is inside the Reconciliation Hash preimage, so an axis whose member form is left open gives one reconciliation two ledger indices. Recording a bare axis over five addressed registers would state that something was stale without stating what, which is not reproducible. The Set is a set rather than a single value: a reconciliation may be qualified on more than one axis, and an encoding admitting only one would force an implementation to choose between them silently. A Reconciliation Output is encoded as a CBOR array in the field order of this section, an absent OPTIONAL or conditionally absent field encoded as CBOR null so that position is preserved and the array's length is fixed. The Per-Register Result Set is an array of arrays, each in the field order enumerated above, under the same rule. The order is normative because the Reconciliation Hash is taken over it, and because a CBOR map would be re-sorted into bytewise lexicographic key order under Section 4.2.1 of , which would override it. The Reconciliation Hash is the SHA-256 digest over that same CBOR array with the Sealing-Key Identifier and Sealing Signature positions encoded as CBOR null. The array's length is unchanged: "excluding" means null-substitution at fixed positions and MUST NOT be implemented as truncation, because a shorter array carries a different CBOR array header and therefore a different digest, and two implementations reading "excluding" the two ways would never agree on a ledger index. It is the value recorded in the Settlement-Layer Ledger, the value a Post-Seal Evaluation Record references, and the retrieval key of . Determinism under Section 4.2.1 of fixes how a given value is encoded. It does not fix which CBOR type a field takes, nor the order of elements within a field that is a set. The Reconciliation Hash is the ledger index of , the retrieval key of , and a value has the requester compute over an Output it has just been handed, so two parties compute it independently and MUST obtain the same value. The types are therefore fixed here, as fixes them for the Agreement Hash and fixes them for a Ledger entry.

Field	CBOR encoding
Reconciliation Event Identifier	byte string of 16 octets
Reconciliation Identifier	byte string of 80 octets, the Claim Hash followed by the Policy-Version Hash followed by the Reconciliation Event Identifier
Claim Hash, Policy-Version Hash, Merkle Root	byte string of 32 octets
Reconciliation Timestamp, Reliance Horizon	text string, in the form fixed below
Combined Verdict	text string, one of the four values of
Verdict Arithmetic and its parameters	two-element array: the operator identifier as a text string, and its parameters as an array, empty for conjunction and disjunction, a one-element array of the threshold as an unsigned integer for threshold-count, and a two-element array of the source-class partition and the per-class threshold for source-class-quorum
source-class partition	array of two-element arrays of the class identifier as a text string and the sorted array of Register Identifiers in that class, the outer array sorted by class identifier
Addressed-Registers Identifier Set	array of Authority Origins as text strings, sorted as states
Bilateral-Register-Agreement Hash Set	array of 32-octet byte strings, deduplicated, sorted
Pattern-Library Version Identifier	text string
Requester-Binding Class	text string
Aggregation-Method Descriptor	text string
Audience Set, Per-Register Result Set, Server-Recorded Divergence-Axis Set	array of arrays, each member in the field order its own section enumerates
Override Record	array in the field order of , or null
Sealing-Key Identifier	two-element array of the Authority Origin as a text string and the JWK thumbprint as a text string
Sealing Signature	byte string, the serialised COSE_Sign1, or null in a preimage
Register Identifier	text string
Answer State, Attested Verdict, Effective Verdict, Non-Answer Reason, Re-Typing Ground, Subject Mapping Descriptor	text string
Divergence-Axis Field	array of two-element arrays of the axis identifier as a text string and its Register Identifier or null, sorted by the deterministic encoding of the member
Query Binding Record, Non-Answer Statement, Projection Record	array in the field order its own section enumerates, or null

The Bilateral-Register-Agreement Hash Set is deduplicated because two addressed registers may be governed by one Agreement, and an implementation that carried the digest twice and one that carried it once would compute two Policy-Version Hashes and two Reconciliation Hashes from identical inputs. Every timestamp this document places inside a digest preimage or a signature payload MUST be expressed in the form YYYY-MM-DDTHH:MM:SSZ: with the Z designator rather than a numeric offset, and with no fractional seconds. admits several renderings of one instant, and a preimage that admits several renderings admits several digests. CBOR rather than : the mandatory-to-implement encoding for a Reconciliation Output is CBOR, and several of its fields are byte strings, for which JSON has no type. Digesting a JSON rendering of it would require a CBOR-to-JSON mapping this document does not define, and two implementations would produce different ledger indices. The Canonical Claim is serialised under and that serialisation is carried as one element of the CBOR array the Claim Hash is taken over; the Reconciliation Output is CBOR throughout. A Reconciliation Output is immutable once sealed. Conditions arising after sealing are recorded under and MUST NOT be represented as fields of the Reconciliation Output.

Output Entitlement and Delivery The Reconciliation Output is the confidential artefact of this protocol and the Settlement-Layer Ledger is its public one. An Output carries subject references, register-signed Partial Attestations and principal identifiers; a Ledger entry carries digests, register origins and structural metadata, and no claim, register-record or principal content. Every rule in this document about who may see what rests on that division, and they are not interchangeable. A party admitted to a Ledger read learns nothing of the subject or the answer. A party holding an Output already holds the content of one reconciliation, and admitting it to reads about that same reconciliation discloses nothing it does not have. Earlier revisions had no answer to who may hold an Output. It was a bearer artefact: possession was the whole of the entitlement, it never expired, and every read predicate this document attempted was expressed in terms of a Requester-Binding that the reader could not present and the Ledger could not evaluate. This section supplies the missing term.

Audience A Reconciliation Output carries an Audience Set of zero or more Audience Members, encoded as a CBOR array which is empty only in the case described below. Each Audience Member comprises:

• an Audience Member Identifier: a URI, in the same identifier space a Requester-Binding uses for an accountable principal, encoded as a CBOR text string. Two Audience Member Identifiers are equal where they do not differ after normalisation under Sections 6.2.2 and 6.2.3 of ; comparison is over the normalised form and is otherwise bytewise, and an implementation MUST encode the normalised form rather than normalise on receipt, for the reason gives for an Authority Origin. It is a sort key inside the Audience Set and so inside the Reconciliation Hash preimage, the first element of every Witness Entry and so inside the Agreement Hash, and the equality target of the quorum rule of ; the same treatment is given to an Operating-Party Identifier and was not given here
• a Verification Method Reference: the JWK thumbprint, computed as in , of the public key under which that member signs a read request under . It MUST be a durable key and MUST NOT be a session credential or a one-time request signature, because the member has to present it long after the reconciliation is over

Audience Members are sorted in bytewise lexicographic order of the deterministic CBOR encoding of the Audience Member Identifier, and each member is encoded as a two-element array in the field order above. Ordering is stated because the Audience Set is inside the Reconciliation Hash preimage, and an unordered set would give one Output as many hashes as it has permutations. The server MUST NOT require proof of possession from a named member at reconciliation time -- the member is typically not present -- and naming one is therefore an assertion by the Requesting Principal, not a fact about the member. Two consequences follow and are stated so that neither surprises. Naming a party places a row in that party's GET /arp/outputs enumeration and in the server's access log that the party did not ask for, so a deployment SHOULD constrain who may be named through the audience constraint below and through the enrolment requirement of . And a member that loses or rotates the key its thumbprint names loses entitlement to every Output that names it, permanently, because the Audience Set cannot be amended after sealing; a member that expects to rely on Outputs over time SHOULD be named by a thumbprint of a key held for that purpose. The Requesting Principal is an Audience Member of every Output performed on its behalf where it can be identified: by its accountable-principal identifier where the Requester-Binding carries one, and otherwise as below. Where it does not -- classes agent-unverified and agent-key-verified -- the Set carries a member whose Identifier is the URI form of the verified signing key's thumbprint. Every requester signs, by , so there is always a key to name and an Audience Set is never empty. Further members are named in the reconciliation request, are enumerated inputs for the purposes of , and are sealed with the rest of the Output. The Audience Set MUST NOT be enlarged after sealing; naming a further member requires a new reconciliation, which is a new question and gets a new answer. A Bilateral Register Agreement MAY declare an audience constraint: a maximum cardinality, a permitted class of member, or both. Where the Audience Set exceeds the constraint an addressed register declares, the reconciliation server MUST NOT transmit a projection to that register and MUST record audience-constraint-exceeded as its Non-Answer Reason. It MUST NOT refuse the reconciliation, and MUST NOT quietly drop the register: the first leaves no artefact stating why, and the second is the addressed-register-cherry-picking exists to prevent. The reconciliation is sealed and, by , cannot reach a decisive Combined Verdict. The requester is not a party to any Bilateral Register Agreement and cannot read the constraint, so it learns the cap from the reason recorded against that register rather than by inspection. A register that attests about a subject is entitled to bound how widely that attestation travels, and a constraint enforced after transmission would be enforced too late. The constraint is enforced by the reconciliation server on the register's behalf and the register cannot verify that enforcement from any artefact this document defines; a register that requires assurance of it should negotiate an audit right in its agreement. A party MUST NOT be treated as entitled to a Reconciliation Output by possession alone. A relying party that has been handed an Output and is not an Audience Member of it MAY verify its Sealing Signature and read its Combined Verdict -- nothing prevents this, and the signature is what makes the Output worth handing on -- but it obtains no read under , learns nothing of supersession or post-seal evaluation, and MUST NOT treat the verdict as current. Reliance without entitlement is reliance on a snapshot of unknown age.

Reliance Horizon A Reconciliation Output carries a Reliance Horizon: a time in the form of , being the Reconciliation Timestamp advanced by the reliance interval the reconciliation server resolves from the policy-epoch store of , keyed on the predicate and the regimes the claim names, exactly as it resolves the Verdict Arithmetic under . A requester able to set its own reliance interval could set its own staleness window, which is the same defect as choosing its own Verdict Arithmetic. After that time an Audience Member MUST NOT treat the Combined Verdict as current without having read the Continuation entries for its Reconciliation Hash under and found no supersession. The Horizon does not invalidate the Output and does not weaken the Sealing Signature: what was sealed remains true of the moment it was sealed. It bounds reliance, not validity. A sanctions no-match is a statement about consolidated lists as they stood, and those lists change on a daily cadence (); an artefact that asserted such a verdict indefinitely and carried no marker of its own staleness would be relied upon indefinitely, which is the failure exists to prevent and could not, having no way to reach the party that had relied. The Reliance Horizon is derived from the Reconciliation Timestamp and is therefore outside the reproducibility requirement of on the same ground.

Delivery The reconciliation server MUST return the sealed Reconciliation Output to the Requesting Principal in the response to the request that commissioned it, in the form states. Where the Adversarial Pre-Transmission Test emitted a Remediation Advisory, the server returns that Advisory and no Output. enumerates the responses to a commissioning request. A refusal under or an audience constraint under is not among them: those refuse a register and not the reconciliation, so an Output is produced and delivered, carrying the reason against the register it concerns. That the server returns the Output is stated because nothing in earlier revisions did. The document specified in detail what an Output contains, how it is sealed, digested, ledgered and notarised, and never that any party receives one. Every discovery path in this document begins with a party holding a Reconciliation Hash, and it holds one because of this paragraph. An Audience Member other than the Requesting Principal is not delivered to. It retrieves under : the server has no channel to a party it has never spoken to, and pushing a confidential artefact to an address named by somebody else is not a mechanism this protocol should define. The Reconciliation Hash is the retrieval key and is not reproducible across runs (), so a party that has discarded it cannot recompute it, and the Reconciliation Identifier is no help because the Claim Hash within it is blinded under and cannot be computed outside the deployment. The server MUST therefore also answer the enumeration of , returning to an authenticated principal the Reconciliation Hashes of the Outputs whose Audience Set names it. Without it, an Audience Member that has lost a 32-byte value has lost every entitlement this section grants it, permanently and silently. The server MUST retain each sealed Output, and MUST answer reads of it and of its Continuation entries, for the retention period, which is the LONGEST period any Bilateral Register Agreement addressed by that reconciliation declares, and in no case ending before the Reliance Horizon advanced by one further reliance interval. Where two agreements declare different periods the longest governs. That direction is specific to a retention period, which is a floor: the shortest declaration would let one register's agreement extinguish another's. Wherever else this document takes a value from a plural set of agreements, the direction is the one that makes the obligation stricter, and it is stated at each site. For every interval that bounds a deadline -- the ledger-head notarisation interval of , and the Evaluation Sweep and supersession deadlines measured against it -- the SHORTEST declaration governs. Taking the longest there would let one permissive agreement postpone every deadline for every other register, which inverts the obligation instead of strengthening it. For the read rate limit of , the most permissive declaration governs, a rate limit being a ceiling on the server's refusals rather than on its duties. The extra interval matters. requires an Audience Member to read before relying past the Horizon, and entitlement is evaluated against the Audience Set of the retained Output; a retention floor that ended exactly at the Horizon would permit the server to discard the basis of that evaluation at the moment the obligation begins, and the member would receive the 404 of -- indistinguishable, by design, from never having been entitled.

Policy-Version-Hash Sealing The Policy-Version Hash MUST commit to:

1. Reconciliation rules
2. Threshold parameters
3. Pattern-Library Version Identifier
4. Applicable-Regimes precedence
5. Verdict-Arithmetic selection, together with every parameter that operator takes
6. The reliance interval from which the Reliance Horizon of is computed
7. Agent-IFF policy identifier and the Requester-Binding
8. Bilateral-Register-Agreement Hashes of the addressed registers

The Policy-Version Hash is the SHA-256 digest over the deterministically encoded CBOR array ["arp-policy-version-v1", Deployment Blinding Value, reconciliation rules identifier, threshold parameters, Pattern-Library Version Identifier, applicable-regimes precedence, [Verdict Arithmetic, its parameters], reliance interval, Agent-IFF policy identifier, Requester-Binding, Bilateral-Register-Agreement Hash Set] in that order, the Hash Set sorted in bytewise lexicographic order of the digests and every other composite element a CBOR array in the order this section states it. It MUST be reconstructible under audit from that array, held in the policy-epoch store. A value every addressed register echoes and every auditor recomputes cannot be left to "a canonical policy state", which earlier revisions were content with and which is not a preimage. The Claim Hash and the Policy-Version Hash MUST each be computed over a preimage that includes the Deployment Blinding Value: a secret of at least 128 bits drawn once from a cryptographically secure random source, persisted in the policy-epoch store, constant for the life of the deployment, and disclosed outside the policy-epoch store only as provides. discharges an auditor's need as far as it can without disclosing the constant that blinds every digest in the deployment, and states what that leaves unverified. It is constant rather than per-claim, and that is what makes it compatible with the rest of this document. The Claim Hash remains a deterministic function of the canonical claim fields within a deployment, so it remains usable as the Settlement-Layer Ledger index and as the retroactive-evaluation key, and the reproducibility requirement of continues to hold: the same deployment given the same enumerated inputs produces the same digests. What changes is that the preimage is no longer guessable from outside the deployment. A per-claim random value would defeat all three properties. Both digests are otherwise taken over low-entropy preimages: a subject identifier is typically a company number of ten or so digits, a predicate is drawn from a published taxonomy, and the accountable principal, agent-IFF policy identifier and verdict arithmetic are each drawn from small enumerable sets within one deployment. Both digests then appear where adversaries can reach them -- the Policy-Version Hash in the protected header of every notarised Signed Statement and in every reconciliation entry of the Ledger, the Claim Hash in the Output and in every Ledger entry of either kind. Without blinding, anyone holding either can recover by exhaustive search the subject that was investigated and the principal that commissioned the reconciliation, which is the disclosure this protocol exists to prevent. Blinding does not weaken reconstructibility under audit, since the Blinding Value is persisted with the state it blinds. A register receives the same Policy-Version Hash as every other addressed register, by . The Blinding Value prevents two colluding registers from recovering the Addressed-Registers Identifier Set from it by search; that they can observe they were addressed together is inherent and is discussed in . Equality is a different matter from inversion. The Requester-Binding is an element of the preimage and every other element is fixed by policy and by the addressed register set, so one requester asking repeatedly about different subjects presents every addressed register with the same Policy-Version Hash. A register cannot recover who that requester is, and can group every reconciliation that requester commissioned against it. Two registers addressed together can join their traffic on the same value, as can any reader of the notarised Signed Statements, in which the hash appears in the protected header. That is a stable requester pseudonym, disclosed to parties otherwise limits to the Requester-Binding Class, and reasoning about the preimage's resistance to search says nothing about it: a correlation handle does not need to be inverted to work. A deployment for which that is unacceptable MUST substitute, in the seventh element, a digest over the Requester-Binding and the Reconciliation Identifier. The Policy-Epoch Store holds both, so an auditor can still reconstruct the preimage, and the element then varies per reconciliation and carries no cross-reconciliation handle. It is stated as a deployment choice rather than a requirement because the constant form is what lets a register recognise a returning counterparty under a bilateral agreement, which some deployments need and others must not have. Discussed further in .

Post-Seal Evaluation Records Two conditions arise after a Reconciliation Output has been sealed and therefore cannot be fields of it, and are not Divergence Axes: a Divergence Axis qualifies a verdict, and these qualify an operation performed on an Output that is already immutable.

• notarisation-incomplete, where notarisation under neither completed nor was refused within the polling bound.
• attribution-indeterminate, where a Retroactive Evaluation could not determine whether a material change arose from a change in policy state or from a change in Source-Data Version.

Each is recorded in a Post-Seal Evaluation Record comprising:

• the Reconciliation Hash of the Output it concerns
• the Post-Seal Evaluation Qualifier, drawn from the registry of
• the Policy-Version Hash and Pattern-Library Version Identifier in force at the time of the evaluation, which may differ from those the Output was sealed under
• a Post-Seal Evaluation Timestamp, in the form of
• an Attribution Account, present exactly where the Qualifier is attribution-indeterminate: a text string stating which of the two candidate causes were examined and why neither could be excluded. A bare qualifier would be a discretionary escape signed by the party that benefits from it
• a Sealing-Key Identifier
• a signature by the reconciliation-server sealing key, a COSE_Sign1 whose payload is the CBOR array of this record with the signature position encoded as CBOR null

A Post-Seal Evaluation Record is encoded as a CBOR array in the field order above, an absent conditionally-absent field encoded as CBOR null so that position is preserved. The Post-Seal Evaluation Record Hash of is the Signing Input Digest of that record's signature. Earlier revisions took it over the array in its entirety with the signature included, on the ground that the digest should be over the artefact as served under . That ground does not hold: under a signature primitive whose encoding is not byte-unique the artefact as served is not one byte-string, and a digest over it names whichever copy the reader was handed. states the measurement. A Post-Seal Evaluation Record MUST be retained by the reconciliation server for the period of , and a Continuation entry of type continuation-post-seal-record MUST be appended to the Settlement-Layer Ledger carrying the record's hash. The hash is not written into the entry that recorded the reconciliation: that entry is already signed and the Ledger exposes no UPDATE. An Audience Member of the Output discovers the record by reading the Continuation entries for its Reconciliation Hash under and retrieves it by its hash under the same binding. The record travels as the result element of the signed read response of ; the media type registered for the record labels it wherever it is carried outside that envelope, and the Post-Seal Evaluation Record Hash is taken over the record itself and not over the response that carried it. A record emitted but not appended would be undiscoverable, which would make the attribution safety valve of unreachable in exactly the case it exists for. A Post-Seal Evaluation Record MUST NOT alter the Reconciliation Output it references, and a relying party MUST NOT treat the existence of one as invalidating that Output. A Reconciliation Output whose notarisation is incomplete remains valid under its Sealing Signature. Where a Sovereign Re-Notification is emitted under for a material change, the notification MUST state whether the change arose from policy state or from Source-Data Version, and where it cannot, a Post-Seal Evaluation Record carrying attribution-indeterminate MUST be emitted and referenced by the notification.

Settlement-Layer Ledger The Ledger carries two kinds of entry. A reconciliation entry records a sealed Reconciliation Output. A Continuation entry records a fact that arose after that Output was sealed and therefore could not be a field of it. Every entry carries an Entry Type drawn from the registry of , and the Entry Type determines which further fields the entry carries. An entry whose Entry Type is not reconciliation is a Continuation entry. Without a discriminator a verifier reading an entry cannot tell which field list to apply, and an entry legitimately lacking a field would be indistinguishable from one that is malformed. Every entry, of either kind, comprises these fields and in this order:

• Entry Sequence Number, a strictly increasing integer with no gaps: the first entry of a chain is 1 and each subsequent entry is its predecessor's plus one. Contiguity is required because the consistency read of cannot otherwise distinguish a sequence number the operator never allocated from one it is refusing to answer for, the two being the same 404 by
• Entry Type, from the ARP Ledger Entry Types registry of
• Claim Hash, the index of
• Reconciliation Hash of the Reconciliation Output the entry concerns
• Entry Timestamp ( UTC), the time at which the entry was appended
• Prior-Entry Hash, being the Signing Input Digest of the immediately preceding entry's Entry Signature; in the first entry of a chain, which has no preceding entry, thirty-two zero octets. It is taken over that entry's signing input and not over the entry as served, so that a reader handed any byte-string carrying that entry's signature computes one value. It still commits to every field of the preceding entry, including that entry's Self-Entry Hash, and to the Sealing-Key Identifier and the algorithm identifier in the protected header, because the Sig_structure covers all of them

followed by the type-specific fields enumerated below, followed by:

• Self-Entry Hash, being the SHA-256 digest over the CBOR array of this same entry with the Self-Entry Hash and Entry Signature positions encoded as CBOR null, encoded under the Core Deterministic Encoding Requirements of Section 4.2.1 of , so that the array's length is the length fixed by the Entry Type and is the same array a verifier already holds. The encoding requirement is stated here and not left to be inferred from : without it a definite-length and an indefinite-length encoding of one entry yield two Self-Entry Hashes, and the head comparison of this section treats that as a fork, which obliges every reader of the second encoding to act under against an operator that equivocated about nothing
• Entry Signature, a COSE_Sign1 by the reconciliation-server sealing key whose payload is the CBOR array of this same entry with the Entry Signature position alone encoded as CBOR null -- so it covers every other field including the Self-Entry Hash -- and whose protected header carries the Sealing-Key Identifier that resolves it

An entry is encoded as a CBOR array in the field order of this section, an absent field -- whether marked OPTIONAL or conditionally absent under a stated condition -- encoded as CBOR null, so that position is preserved and the array's length is fixed by the Entry Type. Absence MUST be encoded and MUST NOT be expressed by a shorter array: two encodings of one entry would otherwise yield two Self-Entry Hashes, which the head comparison of this section treats as a fork. The order is normative because the Self-Entry Hash is taken over it; an encoding as a CBOR map would be re-sorted by key under the Core Deterministic Encoding Requirements of Section 4.2.1 of and would override it. A field whose value is itself a choice -- the second field of a continuation-notarisation entry -- is encoded as a two-element array of a discriminant and a value, the discriminant being the CBOR text string entry-id or refused. The Self-Entry Hash is enumerated after the type-specific fields so that it covers them. Placing it before them would leave a Continuation entry's payload outside it. The Prior-Entry Hash is taken over the preceding entry's signing input rather than over that entry's Self-Entry Hash, so that the Sealing-Key Identifier and the algorithm identifier under which that entry was signed are inside the chain. Were the chain to link Self-Entry Hash to Self-Entry Hash, neither would be covered by anything, and an operator could re-sign every historical entry under a revoked or unresolvable key while every hash in the chain, and every head already published and notarised, continued to verify. The signature bytes themselves are deliberately outside the chain, and this is a change from earlier revisions, which took the Prior-Entry Hash over the whole preceding entry so that Entry Signatures were inside it. That is not recoverable: measures a primitive under which one signing act has many verifying encodings, so a chain keyed on those bytes breaks for a reader handed a different one. What the chain binds is the identity of the signing act rather than the bytes of one encoding of it. Two things earlier revisions detected are no longer detectable and are stated here rather than left to be discovered. Stripping a historical Entry Signature while leaving its protected header and payload intact moves no Prior-Entry Hash. So does re-signing an entry under the same key and header. The Sealing-Key Identifier and the algorithm remain covered, so a re-signature under a different key or algorithm still moves the chain, which is the case the paragraph above is about; a re-signature under the same key does not. An entry is signed exactly once. A second signature over the same fields is a different entry, MUST NOT be appended at the same Entry Sequence Number, and MUST NOT replace the first. Under the Prior-Entry Hash of this section that rule has no verifier-side test, and saying so is better than implying one. A Signing Input Digest is a value per signing input, not per signature, so two signings of one entry share it and yield one chain and one head rather than the two divergent chains an earlier revision relied on to make the violation visible. The rule is therefore an operator obligation an Audit Identity under can examine and a reader cannot, which is the price of the digest being stable under , and is paid deliberately: a rule that is unenforceable against an honest reader is better than a chain that breaks for one. The Entry Timestamp is distinct from the Reconciliation Timestamp. A Continuation entry may be appended weeks after the reconciliation it concerns, and an entry carrying only a Reconciliation Timestamp would state that the notarisation, the post-seal evaluation or the supersession occurred at the moment of the reconciliation, which is false in every case the mechanism exists for. An entry whose Entry Type is reconciliation additionally comprises:

• Policy-Version Hash
• Addressed-Registers Identifier Set, each member an Authority Origin, sorted in bytewise lexicographic order of its UTF-8 encoding
• Aggregation-Method Descriptor
• Merkle Root
• Requester-Binding-Class Descriptor, one of the four classes enumerated in the Requester Identity Binding and Agent Friend-or-Foe Gate section
• Reconciliation Timestamp, as sealed in the Reconciliation Output
• OPTIONAL Source-Reconciliation-Output Identifier, being the Reconciliation Hash of the Output this reconciliation supersedes, present exactly where it supersedes one
• Override Indicator, true exactly where the Reconciliation Output carries an Override Record under the Adversarial Pre-Transmission Test

An entry whose Entry Type is continuation-notarisation additionally comprises:

• Transparency Service Identifier, being the Authority Origin of that service
• exactly one of the EntryID that service returned, or the HTTP status code by which that service terminally refused registration

Only the status code is recorded, never a response body. A body is authored by the Transparency Service, is unbounded, and routinely echoes submitted content; writing one into an append-only log with no DELETE would put text this document does not control inside a record that forbids claim and principal content in the clear. A continuation-notarisation entry MUST be appended where notarisation completes, and where the Transparency Service returns a status the implementation resolves as a terminal refusal under . Where a status cannot be so resolved -- the 404 of carries two meanings and a service is not obliged to distinguish them -- it is not a terminal refusal, and the reconciliation is treated as one whose polling bound was exhausted. In that case no continuation-notarisation entry is appended and the outcome is recorded under as notarisation-incomplete. Requiring an entry only on failure would leave the successful case -- the case the join exists for -- unrecorded. Where an implementation subsequently learns the EntryID of a registration it had recorded as incomplete, it MUST append the continuation-notarisation entry then. This document defines no means by which it would learn that: retrieves by EntryID and the EntryID is precisely what was not received, polling is bounded, and no callback is specified. A notarisation-incomplete record will therefore usually stand permanently, and it is evidence that registration did not complete within the polling bound and not that it failed. That is open. An entry whose Entry Type is continuation-post-seal-record additionally comprises:

• Post-Seal Evaluation Record Hash

An entry whose Entry Type is continuation-supersession additionally comprises:

• Material-Change Indicator, stating whether the Combined Verdict changed materially within the meaning of
• Superseding-Reconciliation Hash, being the Reconciliation Hash of the Reconciliation Output that supersedes the one this entry concerns, present exactly where a superseding Output was produced and absent where the supersession is the revocation of a Verified Principal Credential under , which supersedes an Output without producing another
• Superseding-Entry Sequence Number, being the Entry Sequence Number of the reconciliation entry that records the superseding Output, present under the same condition

No Continuation entry carries a retrieval URI. Every artefact a Continuation entry points at is retrieved under , by hash for a Post-Seal Evaluation Record and by Reconciliation Hash for a superseding Output, from the same authority origin that served the entry. Carrying a URI instead would oblige every reader to dereference an operator-chosen address before it could check anything -- a forced fetch, a de-blinding oracle correlating a reader's network identity with one Reconciliation Hash, and a covert channel that no constraint on the URI's content can close, since host selection and path structure carry the signal without stating anything. It would also put a non-digest field in a Ledger whose whole disclosure argument is that it holds digests. A Reconciliation Output produced by Retroactive Evaluation to supersede an earlier Output MUST carry the Audience Set and the Requester-Binding Class of the Output it supersedes. Without that rule the party entitled to learn that its verdict had changed would be entitled to the entry saying so and not to the Output that says what it changed to, and the traversal would end one step short. Such an Output has no commissioning request and is not delivered under ; it is retrieved. Where the superseding reconciliation addresses a register whose audience constraint the inherited Audience Set exceeds -- which can happen, since the superseding reconciliation may address registers the superseded one did not -- that register is recorded audience-constraint-exceeded under like any other. The Audience Set is not truncated to fit: truncating it would strand the party the supersession exists to notify, and the constraint is satisfied by not obtaining that register's answer rather than by silencing the reader. A party retrieving a Post-Seal Evaluation Record MUST reconstruct the Sig_structure of that record's signature from the protected header and the payload of the retrieved COSE_Sign1, MUST verify that its Signing Input Digest equals the Post-Seal Evaluation Record Hash carried in the entry, MUST verify that signature under the Sealing-Key Identifier the record carries, and MUST discard the record where either check fails. The hash does not cover the signature bytes, so the signature check is not redundant and a record served with a substituted, absent or garbage signature satisfies the digest check alone. Without both checks the hash is decorative and an operator can serve a different record to each audience, reopening at the record the equivocation the Ledger closes at the entry. A Continuation entry carries no Policy-Version Hash, no Addressed-Registers Identifier Set, no Aggregation-Method Descriptor, no Merkle Root and no Requester-Binding-Class Descriptor. Those describe the reconciliation, which the reconciliation entry already records and the Reconciliation Hash already binds; carrying them a second time would create a second place for them to disagree. A Continuation entry MUST carry the same Claim Hash and Reconciliation Hash as the reconciliation entry it continues, and the storage interface layer MUST reject a Continuation entry whose Reconciliation Hash matches no earlier reconciliation entry, returning a rejection the appending subsystem can distinguish from a transport failure. Because Entry Sequence Numbers are allocated in one sequence and secondary stores replicate rather than originate, every store holds the reconciliation entry against which the check is made. Prior-Entry and Self-Entry Hashes establish that no entry has been removed from a chain; they do not establish that only one chain exists. Signing each entry makes a second chain attributable rather than merely possible. A Reconciliation Output is sealed before it is notarised and so cannot itself carry the EntryID, and the Ledger exposes no UPDATE, so the join cannot be made by amending the original entry. It is made by appending. Without it a successful notarisation would be unlinkable to the reconciliation from every side, since retrieval is by EntryID and offers no query surface. A continuation-supersession entry MUST be appended against the superseded Output on every supersession, whether or not the change is material. Where the supersession produced a superseding Output, the superseding reconciliation entry MUST also carry the Source-Reconciliation-Output Identifier naming what it replaced, and the two records are inverse pointers over one relation. Where it did not -- the revocation of a Verified Principal Credential -- there is no superseding entry and no second record, and the Continuation entry stands alone. The Material-Change Indicator distinguishes a material supersession from an immaterial one in either case. imposes the further obligation of a Sovereign Re-Notification where the change is material; it does not condition the ledger record, which is written either way, since a party relying on a superseded Output needs to know it was superseded before it can be told the change was immaterial. Where both records exist they are inverse pointers over one relation and neither substitutes for the other. A party holding the superseded Output cannot follow a pointer that exists only on an entry it has not been returned, and a regulator whose scope under covers the superseded reconciliation is not thereby returned the superseding one, whose addressed registers and therefore whose agreements may differ. The constraint is on what a reader is returned, not on what a store holds. The Ledger MUST NOT store Canonical-Claim content, register records, Partial-Attestation payloads, or any principal identifier in the clear; the requester's accountable principal is committed only through the Policy-Version Hash. The append-only constraint MUST be enforced at the storage interface layer. The Ledger interface MUST expose APPEND and READ operations only, with no UPDATE and no DELETE operation exposed or implemented. Retroactive Evaluation and the derivation-chain invariant check are subsystems of the reconciliation server and read the Ledger without scope restriction. Every read by a party outside the reconciliation server is served under , which states the operations, the entitlement each requires, the response form, and the error semantics. Three entitlements reach the Ledger: a regulator's, governed by ; an Audience Member's under ; and an Audit Identity's under . A Register Operator holds the narrower entitlement of the consistency check below. An Audience Member is entitled to the Continuation entries carrying the Reconciliation Hash of an Output that names it, and to the reconciliation entry carrying that same Reconciliation Hash. It is entitled to no other entry. This is the predicate earlier revisions could not express. It is evaluable, because the Audience Set is a sealed field of the Output and the server retains the Output under ; the Ledger is not asked to evaluate it, and could not, since it stores no principal identifier in the clear. It admits the right party, because entitlement follows the Output rather than the request, so a member the Requesting Principal named at reconciliation time is admitted and a party that merely came into possession of the artefact is not. And it survives the events that broke its predecessors: an Audience Member's verification method is required by to be presentable after the fact, and revocation of the Requesting Principal's Verified Principal Credential does not remove the other members of the Audience Set, so the supersession entry recording that revocation has a reader. Where an Output's Audience Set is reduced to members that can no longer authenticate -- a single-member Set whose sole member's credential has been revoked -- its Continuation entries are reachable only through the Regulator Portal. The reconciliation MUST still have been performed with a Requester-Binding class recorded under , so the condition is visible to the regulator that scope serves. An Audience Member's read discloses only facts about a reconciliation whose full content it already holds: that a supersession or a post-seal evaluation exists, what it points to, and the ledger position of each. The one exception is worth naming, because it is not obvious: a Post-Seal Evaluation Record carries the Policy-Version Hash and Pattern-Library Version Identifier in force at the time of the evaluation rather than at sealing, and those are values the member did not previously hold and, being stable within a deployment, are durable correlators. That is a deliberate disclosure to a party already entitled to the reconciliation they qualify, and it is bounded by 's rule that a register may cap how wide an Audience Set addressing it may be. Where the Ledger is replicated per , each secondary store MUST be able to demonstrate that its chain and every other secondary store's chain share a common prefix. A common-prefix demonstration between stores under one operator is that operator attesting to itself. The reconciliation server MUST therefore publish a signed Ledger Head Statement at /.well-known/arp-ledger-head on its Authority Origin. It is republished once per notarisation interval and not on every append: the resource is unauthenticated and carries a contiguous sequence number, so a continuously updated head would hand any observer the deployment's exact entry count, its write rate and the timing and size of every retroactive supersession burst -- the aggregate disclosure rate-limits the authenticated surface to prevent. A Statement comprises:

• the Entry Sequence Number of the current head
• the Self-Entry Hash of that entry
• the Entry Timestamp of that entry
• a Statement Timestamp, being the time the Statement was produced, in the form of . Without it two Statements published across a quiet period differ only in their notarisation pointer and neither is dateable, so the interval a register negotiated is unverifiable from the artefact
• a two-element array of the Transparency Service Identifier and the EntryID of the most recent completed notarisation of a Ledger Head Statement, encoded as CBOR null until the first such notarisation completes
• a signature by the reconciliation-server sealing key over the foregoing, carrying the Sealing-Key Identifier that resolves it

A Ledger Head Statement is encoded as a COSE_Sign1 over the deterministically encoded CBOR array of the first five items above, in that order, under the media type registered in , with the fifth item encoded as CBOR null until the first notarisation completes. The server MUST submit the Ledger Head Statement current at each interval for notarisation by a SCITT Transparency Service. The interval is the shortest declared by any Bilateral Register Agreement, per the direction rule of . The Transparency Service MUST be one every Bilateral Register Agreement the deployment holds declares, and MUST NOT be operated by or under the control of the reconciliation server or any party controlling it. A notary the operator owns is the operator attesting to itself, which is the condition this mechanism exists to escape; the same requirement governs the notarisation of Evaluation Sweep Statements under . It is not registered under the binding of , which is scoped to sealed Reconciliation Outputs and whose protected header requires a Policy-Version Hash and a Bilateral-Register-Agreement Hash that a head statement does not have; it is registered as a Signed Statement under its own media type. Statements published between intervals are not notarised. Entry Sequence Numbers are allocated in a single sequence for the logical Ledger. A secondary store under replicates that sequence and MUST NOT allocate independently, or two conforming stores would present the same sequence number over different entries and be indistinguishable from a fork. The Entry Sequence Number is what makes two heads comparable. A bare hash cannot distinguish a fork from ordinary progress: two parties who have each seen a different head learn only that the values differ, which is the expected case whenever they observed at different times. Two Head Statements bearing the same Entry Sequence Number and different Self-Entry Hashes are therefore a fork on their face, and both are signed, so both are attributable. Two Head Statements bearing different sequence numbers are reconciled by the consistency read of . A party entitled to that read -- a Register Operator or a regulator -- presents the lower of the two sequence numbers and receives the Self-Entry Hash of the entry at that position in a signed response bound to the request it answers. The two views agree only where that value equals the one the lower Head Statement carried, and where they disagree the party holds two signed statements by one key that cannot both be true of one chain. That is why the response is signed and bound to its request: an unsigned answer would let an operator serve each questioner from that questioner's own branch and leave the questioner with nothing it could show a third party. The rate limit of is load-bearing on that operation and not merely hygiene. The consistency read ranges over every sequence number up to the head; swept without limit it yields the deployment's exact entry count by binary search, its write rate by polling, and the timing and size of a retroactive supersession burst by watching for a step change -- none of which any single answer discloses. A party that holds two irreconcilable signed statements MUST cease to rely on any Reconciliation Output sealed by that server after the lower of the two sequence numbers, MUST report the pair to every regulator whose Bilateral Register Agreements it can identify from the Outputs it holds, and MUST NOT treat the server's subsequent statements as evidence of anything until the discrepancy is resolved. A Register Operator that holds such a pair MUST additionally refuse further Per-Register Claim Projections from that server, on which the server records agreement-drift-suspended against that register under as it would for any other suspension. Detection without a required response leaves the mechanism ending in a held contradiction and no consequence. Two limits remain and are stated rather than claimed away. An operator that publishes to two audiences at disjoint sequence numbers never emits a colliding pair, so detection by collision is opportunistic even though reconciliation by consistency read is not. And a party holding neither a Reconciliation Output nor a Bilateral Register Agreement has no register set against which to anchor the signing key under : it can check that a Head Statement is signed and not that the signer was entitled to publish it. Both bear on a party outside the entitled set; a Register Operator, which is the party with standing to care whether its attestations sit on one chain, has the agreement that anchors the key and the entitlement that completes the check.

Replication The Ledger MAY be distributed across a plurality of per-jurisdiction secondary stores under synchronous replication, each operated under the data-residency constraints of its host jurisdiction. The append-only derivation-chain invariant -- that every entry's Prior-Entry Hash equals the Signing Input Digest, as defines it, of the immediately preceding entry's Entry Signature -- MUST be preserved across all secondary stores. A secondary store replicates the single sequence of and originates no entry of its own.

Regulator Portal The Regulator Portal Subsystem authenticates a sovereign regulator's jurisdictional credentials against a regulator-identity-provider trust anchor that MUST be declared in every Bilateral Register Agreement addressed by the reconciliation being read. It restricts returned fields to those within the regulator's statutory scope as declared in the statutory-regulator-access scope of those agreements. Each Bilateral Register Agreement declares, per regulator jurisdiction, a permitted-read-field set: the names of the Reconciliation Output and Ledger entry fields a regulator of that jurisdiction may be returned, and the predicates over which it may be returned them. The scope restriction is the INTERSECTION of the per-agreement permitted-read-field sets scoped to the regulator's jurisdiction, taken only over reconciliations whose Canonical Claim Predicate is in the intersection of the corresponding permitted-read-predicate sets, and further intersected with the regulator's requested field set. Fields and predicates are different domains and are intersected separately; intersecting one with the other would yield the empty set, which earlier text did. Each access MUST be recorded in an append-only audit trail. Each record MUST carry a contiguous sequence number and the digest of the preceding record, computed as computes a Prior-Entry Hash, and the reconciliation server MUST publish a signed head of that trail -- its current last sequence number and digest, under its sealing key -- once per ledger-head notarisation interval, and MUST submit that head for notarisation by the Transparency Service of . Earlier revisions called the trail subpoena-grade and specified none of that. The trail is held by the party whose reads it records, and the accountability of the Audit Identity entitlement rests on it -- an unaudited audit right is a standing unaccountable read. Without a chain and an externally anchored head, a record can be removed or rewritten by the party the trail exists to hold accountable, and it is then evidence only against a party that has not tampered with it. This document applies exactly this construction to the Settlement-Layer Ledger a few sections above and applied none of it here, which is the whole of the defect: not a technique the document lacks, a technique it did not carry to the second place that needed it. The Portal is a subsystem of the reconciliation server and reads the Ledger without scope restriction. The scope governs what it RETURNS, not what it may read. Stating it the other way round would make the Portal unable to compute the authority under which it answers, since that computation requires reading the entry first. Where the entry read is a Continuation entry, the Portal computes the trust anchor and the scope from the agreements addressed by the reconciliation entry carrying the same Reconciliation Hash. A Continuation entry names no registers of its own, and an intersection taken over an empty set of agreements would either deny every regulator or restrict none, which are the two failures the rest of this section exists to avoid. The fields a Continuation entry carries are structural: an entry type, a sequence number, a timestamp, chain hashes, and a pointer to an artefact. None is a register record, a claim value or a verdict. A regulator in scope for a reconciliation entry is therefore in scope for every field of every Continuation entry carrying that entry's Reconciliation Hash, without any agreement having to enumerate those fields. The alternative -- intersecting a set of field names no agreement mentions -- yields the empty set, and would make a Sovereign Re-Notification arrive at a regulator that is then returned nothing when it follows the pointer. Agreements negotiated before this revision name none of these fields, and forbids retroactive evaluation from requiring any agreement to be renegotiated. Both intersections are load-bearing. Taking the union across agreements would let one register operator's permissive agreement widen what a regulator may read about a reconciliation that also addressed a restrictive register, inverting the data-residency property this protocol exists to preserve; and requiring the trust anchor in only one agreement would let a single register operator unilaterally introduce a regulator identity that authenticates against multi-register events. Intersecting with the requester's own requested set is not itself a restriction, since the requester chooses it.

Sovereign Re-Notification A Sovereign Re-Notification is a COSE_Sign1 by the reconciliation-server sealing key, under the media type registered in , whose payload is the CBOR array of:

• the Claim Hash and the Reconciliation Hash of the superseded Output
• the Entry Sequence Number of the continuation-supersession entry recording the supersession
• the Material-Change Indicator
• the verdict values before and after
• the Attribution, one of policy-state, source-data-version or attribution-indeterminate, and where it is the last, the Post-Seal Evaluation Record Hash of the record requires
• a Notification Timestamp, in the form of

encoded as a CBOR array in that order, an absent conditionally-absent element as CBOR null so that the array's length is fixed, the first element a two-element array of the two hashes and the fourth a two-element array of the verdict before and after; and signed under the Sealing-Key Identifier its protected header carries. The signature is not a payload element. The server MUST deliver it to the notification endpoint each affected regulator's Bilateral Register Agreements declare, MUST retry until acknowledged or until the retention period of elapses, and MUST make every Re-Notification retrievable by a regulator under . A regulator that is unreachable when a verdict changes is exactly the case the mechanism exists for, so delivery cannot be a single attempt, and an obligation with no artefact and no endpoint -- which is what earlier revisions specified -- is an obligation no party can discharge or audit.

Audit Path Several requirements in this document are justified by what an auditor can reproduce: the re-typing decision of "without the server's assurance", the Query Binding of , the Policy-Version Hash "under audit" of , and the Deployment Blinding Value of . No earlier revision defined that path, so every one of those justifications rested on a party the document did not admit. Each Bilateral Register Agreement MUST declare at least one Audit Identity: an identifier and a key thumbprint, in the form uses for an Audience Member. A party authenticating as an Audit Identity under is entitled to:

• every operation of , unredacted, over any reconciliation addressing the register whose agreement declares that identity
• the Reconciliation Outputs of those reconciliations, irrespective of their Audience Sets, by GET /arp/outputs/{reconciliation-hash}
• for a named reconciliation, every element of the Policy-Version Hash preimage of EXCEPT the Deployment Blinding Value, together with a Reconstruction Proof: a keyed digest, computed as HMAC with SHA-256 under the Deployment Blinding Value over the deterministically encoded CBOR array ["arp-reconstruction-v1", P], where P is the Policy-Version Hash preimage array of with its Deployment Blinding Value position encoded as CBOR null so that the array's length is preserved. It is served as the two-element array of the disclosed elements and the proof, as the result of GET /arp/outputs/{reconciliation-hash} where the requester authenticated as an Audit Identity. An auditor given the Value recomputes it; one not given the Value can only compare it against another proof the same server produced. The preimage is pinned here because it was not pinned anywhere. The sweep recorded in the Document History put every digest preimage and signature payload in this document into a CBOR array with a normative field order and null-substitution for absent fields, and enumerated the artefacts it had reached; this construction was not among them. It had no array, no domain-separation string, no field order, no rule for the excised element and no encoding requirement, and it also had no wire representation, since defines that operation as returning the sealed Output and defines no slot for a value served beside one

An Audit Identity is NOT given the Deployment Blinding Value, and is not given the preimage in full, because the preimage contains it. The Value is one deployment-wide constant and its holder can invert every Claim Hash and Policy-Version Hash on the published Ledger by the exhaustive search describes, including those of reconciliations the auditor's own register had no part in; every agreement declares an Audit Identity, so disclosing the Value to one would disclose the deployment to all of them. An Audit Identity that does not hold the Deployment Blinding Value compares one value the server produced against another value the server produced, under a key only the server holds, over material that neither the Sealing Signature nor any Ledger entry commits to. Equality establishes that the server was self-consistent across the two reads and establishes nothing further. It does not establish that the disclosed policy elements are the ones sealed into the Policy-Version Hash, because a server that sealed under one policy state and later disclosed a different one computes a consistent pair with no more effort than an honest one does. And it does not establish that the resulting hash is correct. Only an Audit Identity given the Value can establish either. An earlier revision stated the first half as established and only the second as open, which was one step too generous: it granted the mechanism the property that a proof minted by the audited party, under the audited party's secret, over material nothing else commits to, tells a third party something about the world. A deployment that requires the stronger property MUST appoint an Audit Identity jointly with every register whose agreement it holds, and MAY disclose the Value to that joint identity alone. This document states the limit rather than resolving it, because a construction that let one register's appointee verify a deployment-wide digest without holding the deployment-wide secret is a different mechanism than the one specified here. An Audit Identity is declared in an agreement rather than named by a requester, because the party being audited must not choose its auditor after the facts are known, and because the register whose records are at issue is the party with standing to insist on one. Its entitlement is scoped to reconciliations addressing that register: an auditor appointed under one agreement reads nothing about a reconciliation that agreement had no part in. Every access under an Audit Identity MUST be recorded in the append-only audit trail of . An unaudited audit right is a standing unaccountable read of every Output a deployment holds.

Retroactive Evaluation Upon publication of an updated Pattern Library, an updated Policy Version, or a new Source-Data Version for any list a register consulted under , the Retroactive Evaluation Subsystem MUST execute a deterministic re-application of the updated state to the retained metadata of historical Reconciliation Outputs -- the Per-Register Result Set, the resolved arithmetic and its parameters, and the Source-Data Version Identifiers, being the inputs from which a Combined Verdict is recomputed. Under a Pattern-Library or Policy-Version trigger the set to be examined is every retained Output whose Policy-Version Hash preimage, as the Policy-Epoch Store of holds it, carries a value the transition changed. A Policy-Version Hash is not superseded as a value: its seventh element is that reconciliation's Requester-Binding, so it is per-reconciliation and there is no current hash against which to compare one. What a transition supersedes is a preimage element, and the store holds every preimage. Earlier revisions selected on "a superseded Policy-Version Hash", which named no determinate set and left the operator to choose which Outputs its own policy change had reached. Under a Source-Data Version trigger the policy state is unchanged and that set would be empty; the set is instead those Outputs whose Per-Register Result Set carries a Source-Data Version Identifier from the list that was republished. Under a credential-revocation trigger it is those whose Requester-Binding rested on the revoked credential. Under a register-record-correction trigger, being a statement by a Register Operator under item 32 of that a record it attested has been corrected, the set is those Outputs carrying a Partial Attestation from that register over the corrected record. The fifth trigger is new in this revision and the gap it closes is the one a subject would care about most. A source-data-version trigger reaches a corpus-level republication whose state identifier the list publisher assigns and which must be identical across every attestation over that list; it does not reach a register correcting one record about one person. So a beneficial-ownership register carrying an erroneous ownership percentage could produce a match on a sanctions-linkage predicate, correct the record the following week, and no trigger would fire, no sweep would run and no supersession would be appended. An Audience Member reading Continuations before relying past the Reliance Horizon would correctly find nothing, and the verdict built on the error would stand. states that a rectified verdict is expressed by supersession rather than by deletion, and until this revision no trigger produced one. Where permissible under the applicable Bilateral Register Agreements, partial attestations MAY be re-invoked. The retroactive evaluation MUST be executable without re-negotiation of any Bilateral Register Agreement. A material change in a historical Combined Verdict -- defined as any change of verdict value into, out of, or between the decisive values, the decisive values being match and no-match -- MUST trigger a Sovereign Re-Notification through the Regulator Portal, and MUST additionally be recorded as a Continuation entry of type continuation-supersession against the superseded Output, under the field rules of , so that a party which acted on the superseded Output can discover that it was superseded. Notifying only the regulator would leave the party that acted on a verdict the last to learn it had changed. A transition from no-match to match is material: it is the case the protocol's motivating domain cares most about, and a definition that excluded transitions within the decisive class would omit it. Revocation of a Verified Principal Credential relied upon in a historical reconciliation is itself a material change: the Retroactive Evaluation Subsystem MUST re-derive the affected Requester-Binding class and, where a decisive reconciliation was performed for what is now an unverifiable requester, emit a Sovereign Re-Notification.

Evaluation Sweep Statements Every trigger of retroactive evaluation is observed by the reconciliation server, every decision to run is taken by it, and until this revision nothing recorded that a sweep had run. "We evaluated and found no change" and "we never evaluated" were the same observation from every position outside the server, which made the central obligation of this section unfalsifiable. The Retroactive Evaluation Subsystem MUST emit exactly one Evaluation Sweep Statement for each trigger, within the ledger-head notarisation interval of measured from the trigger event. One Statement per trigger, on a deadline tied to an event outside the server, is what makes a missing Statement provable; "one per sweep" would let an operator batch a quarter's triggers into a single Statement and remain conformant while evaluating nothing in time. A Statement comprises:

• the trigger, drawn from the registry of and initially one of pattern-library, policy-version, source-data-version, credential-revocation or register-record-correction, and the identifier of the artefact that triggered it
• the Policy-Version Hash and Pattern-Library Version Identifier applied
• the Entry Sequence Number of the Ledger head when the sweep began and when it completed
• the Excluded-Range Set: the set of Entry Sequence Number ranges inside the bracket that the sweep deliberately did not examine, each a two-element array of a range and a reason drawn from the registry of , empty where the sweep examined its whole bracket
• the Examined-Range Set: the set of Entry Sequence Number ranges the sweep covered, each a two-element array of a first and a last Entry Sequence Number inclusive, the ranges pairwise disjoint and in ascending order, and together covering every entry between the two head sequence numbers above whose Entry Type is reconciliation
• the count of Reconciliation Outputs examined, and the count found materially changed
• the Examined-Set Root: the root of a Merkle tree, constructed as defines it, over the Claim Hashes of the Reconciliation Outputs examined, sorted in bytewise lexicographic order, so that a party entitled to one of those reconciliations can be shown an inclusion proof that its own reconciliation was in the set. The Root commits to the distinct Claim Hashes examined and to nothing else. By the leaf count and the examined count are not derivable from one another, because two Outputs over one claim share a Claim Hash and the leaves are deduplicated; and no construction in this document commits the count found materially changed to anything beyond this Statement's own signature. Both counts are therefore assertions of the signing server, which the signature, the Timestamp and the notarisation make attributable and dated, and do not make verifiable. An earlier revision said the counts "are not bare assertions", which the deduplication rule two sections above already contradicted. The Examined-Range Set and the identity below are what make them checkable, by measuring them against the Ledger rather than against the Root
• an Evaluation Sweep Timestamp, in the form of
• the Transparency Service Identifier and EntryID of the notarisation of the previous Evaluation Sweep Statement, encoded as CBOR null in the first Statement of a series
• a Sealing-Key Identifier
• a signature by the reconciliation-server sealing key, a COSE_Sign1 whose payload is the CBOR array of the fields above in the order listed, with the signature position encoded as CBOR null, an absent field likewise, encoded under Section 4.2.1 of . The first, second, third, fourth and seventh items are each a two-element array, so that a field carrying two values occupies one position

Statements are retrievable under and MUST each be notarised into the Transparency Service of under their own media type, within the same interval that bounds their emission. The previous- notarisation pointer above makes the published series a chain, so that a withdrawn Statement is detectable rather than merely absent; retrieves by EntryID and offers no query surface, so a party not told an EntryID could not find that notarisation by search. A Statement is retained for the retention period of . On request under , a server MUST return an inclusion proof of a given Claim Hash in the Examined-Set Root of a given Statement, to a party entitled to a reconciliation carrying that Claim Hash. The sweep identity. For every Evaluation Sweep Statement, a party able to read the Ledger over the Statement's Examined-Range Set MUST be able to verify all three of the following, and a Statement failing any of them is non-conforming:

1. The bracket abuts the previous one. The beginning head sequence number equals the completing head sequence number of the Statement this one names as its predecessor, or the Statement is the first of its series. Without this the identity below is an accounting over an interval the operator chose after seeing what was in it, and a sweep can be complete over a bracket that begins after the entries it would rather not have examined. The Examined-Range Set answers was anything skipped inside the bracket; this answers was the bracket cut, and the second question is the one an operator with something to hide would prefer nobody asked.
2. The Examined-Range Set and the Excluded-Range Set together are contiguous over the interval claimed: the ranges are pairwise disjoint, ascending, and their union contains every Entry Sequence Number between the two head sequence numbers whose entry is of Entry Type reconciliation. A range the sweep chose not to examine is therefore individually disposed, with a reason, rather than absent -- a remainder that reconciles only by arithmetic being exactly what declines to accept, one level down. A gap is a claim to have examined an interval with a hole in it, and it is visible because the Ledger is contiguous by construction.
3. The count of Reconciliation Outputs examined equals the number of reconciliation entries in the Examined-Range Set alone.
4. The count found materially changed equals the number of continuation-supersession entries appended in the interval between the two head sequence numbers whose superseded Reconciliation Hash is one of a reconciliation entry in that union.

The four together are an accounting identity rather than a signature, and that is the point of them. A signature makes an assertion attributable; an identity makes it checkable against something the asserting party does not solely control. The Ledger is append-only, contiguous, head-notarised into a Transparency Service outside the operator's control, and read under by regulators, Audience Members, Register Operators and Audit Identities. Requiring the counts to balance against it converts two numbers the operator could previously choose into two numbers the operator must now make true, and a sweep that examined less than it claims fails the identity at whichever of the three it falsified. The first of the four was added after Walter Hawkins showed, on the SCITT mailing list on 20 August 2026, that an equivalent rule one level down constrains the remainder inside a declared population and says nothing about where the population's edge falls. His sentence for it is the one worth keeping: the information did not survive being moved from the remainder to the denominator, it just moved. An operator that may choose the bracket has the same freedom as one that may choose the denominator, and every rule below the first was satisfiable over a bracket selected after the fact. The Examined-Set Root and the Examined-Range Set answer different questions and both are needed. The Root proves membership: an Audience Member can be shown that its own reconciliation was in the examined set. The Range Set proves coverage: any Ledger reader can see that no interval was skipped. A Merkle root over a set of Claim Hashes cannot prove coverage, because Claim Hashes are sparse in the digest space and a set commitment has no notion of the elements that are missing. Entry Sequence Numbers are dense and contiguous, so absence in that space is visible in a way absence in the digest space is not. Committing to the same sweep in both spaces is what lets one artefact answer both questions. A Statement does not prove a sweep was performed honestly, and this document does not claim it does. What it changes is that a sweep not performed is now a statement the operator has to make, sign and date, rather than a silence. A Source-Data Version publication is a public event with a public timestamp; an operator with no Statement within the deadline has not evaluated in time, which is checkable. The other three triggers are not public events, so the Policy Parameters Document of carries the identifier and effective time of every Pattern-Library and Policy-Version transition the server applies, which makes those two triggers observable. A credential-revocation trigger is observable to the credential's issuer and to the affected principal and to nobody else, and this document does not make it more so. The fifth trigger, register-record-correction, is a statement by a Register Operator under item 32 of , so the event that starts its clock is outside the reconciliation server in the same way a list publication is, and the argument reaches it. The falsifiability argument therefore holds for four triggers in five, and it holds for the second and third of them only through the anchoring places on the Policy Parameters Document itself, which is stated here because an earlier revision of this section claimed three in four while the Document carrying two of them was published by the reconciliation server, under its own key, with no publication time and no notarisation. On that footing the count was one in four and the sentence claiming otherwise was the one place this document rounded up. A transition simply omitted from the array started no clock, and no party could date the Document well enough to show that it had been. The Publication Timestamp, the notarisation, and the obligation to republish on the interval whether or not anything changed are what make the second and third arguments true, and a deployment whose Policy Parameters Document is not anchored as requires has two falsifiable triggers and not four. Both counts in this paragraph were stale within two hours of the fifth trigger being added, in opposite directions: the enumeration above still named four triggers while the registry of named five, and this sentence still said three in four. Neither needed a reader to catch. A count in a specification is an assertion about the specification, and the conformance class of now carries a runner that checks every such count against the text that makes it. An operator that signs a Statement it did not earn is making a false attributable claim, which is a different thing from an invisible omission, and the Examined-Set Root means an Audience Member can require it to prove that its own reconciliation was in the set it claims to have examined. Where a Sovereign Re-Notification cannot state whether a material change arose from policy state or from Source-Data Version, the attribution-indeterminate Post-Seal Evaluation Record it references MUST state which of the two candidate causes were examined and why neither could be excluded. A bare qualifier is a discretionary escape signed by the party that benefits from it.

Revocation and the reliance window Revocation of a Verified Principal Credential cannot be detected at the moment of reliance by a party that is not checking, and this protocol does not put a revocation check in the hot path of every relying party. What it does instead is bound the window. An Audience Member MUST read the Continuation entries for a Reconciliation Hash under before relying on that Output past its Reliance Horizon (), and the supersession that records a revocation is among the entries that read returns. Reliance inside the horizon on a credential revoked during it is possible and is not prevented; reliance years later on an Output whose principal was disowned the following week is prevented, which is the case that matters and the case earlier revisions left open. The horizon is declared per predicate, so a deployment needing a shorter window for a sanctions predicate than for a corporate-registry one sets one.

Coverage Probes Every mechanism in this section makes a sweep that was not performed into a statement an operator has to sign and date. None of them establishes how much of what should have been examined actually was. The sweep identity of closes the gap between the counts and the Ledger; it does not close the gap between the Ledger and the world, because an operator that never wrote an entry has nothing to be caught balancing. That is the omission problem, and it does not have a proof. It has an estimator. The construction. A Coverage Probe is an ordinary reconciliation, commissioned by an Audit Identity under , that is indistinguishable at the reconciliation server from any other reconciliation over the same predicate and register set. Before commissioning a set of probes, the Audit Identity publishes a Probe Commitment: a COSE_Sign1 under its own key whose payload is the Merkle Root, constructed as defines it, over the Claim Hashes of the probes it intends to commission, together with their count and a Commitment Timestamp. The commitment is published before the first probe is commissioned and MUST be notarised into the Transparency Service of . After a sweep that should have covered them, the Audit Identity requests an inclusion proof for each probe's Claim Hash under the Examined-Set Root of the Statement covering the interval its probe fell in, which already obliges the server to return. The recovery fraction is the number of probes for which a valid inclusion proof was returned, over the number committed. What it estimates. The recovery fraction is an unbiased estimator of the proportion of eligible Outputs the sweep actually examined, provided the server cannot distinguish a probe from an ordinary reconciliation. Applied to the examined count the Statement asserts, it yields an estimate of the population that should have been examined and was not: where a sweep asserts E examined and recovers m of k probes, the eligible population is estimated at E * k / m, and the shortfall at E * (k - m) / m. This is not a proof about any individual Output and this document does not claim it is. It is a bound on an aggregate, with a confidence interval that narrows as k grows, and it is the only thing in this document that speaks to the size of what was never written down. An operator suppressing a class of reconciliations suppresses probes at the same rate, because it cannot tell them apart, and the suppression appears in the recovery fraction rather than in any artefact the operator controls. Indistinguishability is the whole of the mechanism, and it is what makes it expensive. A probe MUST address real registers over a real predicate and MUST be charged against a real query budget, and its subject MUST be drawn from the same distribution as ordinary subjects for that predicate. A server that can identify probes by their subject, their register set, their timing, their requester or their budget treatment can examine those and suppress the rest, and the estimator then reports the operator's discrimination rather than its coverage. A deployment MUST NOT exempt a probe from any charge, limit or path that applies to an ordinary reconciliation, and MUST NOT mark one as a probe in any artefact before the sweep it tests has been notarised. Why the commitment precedes the probes. Without it, an auditor could commission many probes, observe which were examined, and publish only those it liked, in either direction: an auditor hostile to an operator publishes only the misses, and an auditor captured by one publishes only the hits. The commitment fixes the denominator before the numerator is knowable to anybody, which is what makes the fraction evidence rather than a selection. What it costs and what it cannot do. Probes consume register capacity, and a register bears that cost without receiving the benefit, so the number of probes is a term for a Bilateral Register Agreement rather than a constant this document sets; item 33 of carries it. The technique establishes nothing about a deployment whose registers are themselves suppressing, since a probe's answer is only as good as the register's. And it cannot reach a reconciliation that was never commissioned by anyone, which is the requester's vantage and not the auditor's. The estimator is standard practice in fields that must characterise a survey they cannot repeat: sources of known brightness are injected into an astronomical image and the fraction recovered gives the survey's completeness function; marked individuals are released into a population and the fraction recaptured bounds the population that was never seen. In both cases the quantity of interest is what the instrument missed, which cannot be observed directly and can be estimated from a known signal passed through the same instrument. A retroactive evaluation sweep is an instrument of that kind.

Cryptographic-Primitive-Upgrade Path Each Bilateral Register Agreement MUST declare a Cryptographic-Primitive-Upgrade Path comprising an ordered equivalence list for each of three primitive classes: claim-encryption, partial-attestation-signature, and sealing-signature. The equivalence list MUST include at least one post-quantum primitive for each class, drawn from a set including ML-KEM for key encapsulation and ML-DSA for signature operations. A primitive rotation MAY be executed simultaneously across the three layers without bilateral renegotiation. The Settlement-Layer Ledger remains continuous across the rotation because Ledger entries commit to hashes of canonicalised content rather than to cryptographic identities. The Entry Signature and the Sealing-Key Identifier it carries are the exception, and a verifier MUST resolve the Sealing-Key Identifier carried by each entry rather than assume one key across the chain. An entry signed under a superseded primitive remains verifiable under the key that identifier resolves. The chain is unbroken across a rotation, but not because it is independent of the primitive: the Prior-Entry Hash of is the Signing Input Digest of the preceding entry's Entry Signature, so it depends on the algorithm identifier in that signature's protected header, which the Sig_structure covers. It does not depend on the signature bytes, and that is deliberate. Earlier revisions took the Prior-Entry Hash over the whole preceding entry including its Entry Signature and argued the chain was unbroken because those bytes "are fixed at the moment the entry is appended and are never rewritten". Fixed for the operator, and not unique: measures a primitive under which one signing act has many verifying encodings, so the bytes a reader is handed are not the bytes the operator appended and a chain keyed on them breaks for that reader alone. A verifier recomputing a Prior-Entry Hash across a rotation boundary takes the protected header and the payload byte strings from the preceding entry's COSE_Sign1 verbatim and constructs the Sig_structure around them. It MUST NOT re-encode the protected header: those bytes are the signer's and are what the signature covers, and a verifier that re-encoded them would compute a different digest wherever its encoding differed from the signer's, and could not encode a rotated primitive's header parameters at all without implementing that primitive. The verifier therefore parses a COSE_Sign1 but needs no knowledge of the primitive under which it was signed, and in particular need not verify it. That is more than earlier revisions asked, which was to copy the preceding entry's bytes and hash them; the additional requirement is COSE parsing, and it is the price of a digest that does not move when the signature encoding does.

The Bilateral Register Agreement A register is addressable under this document only through a Bilateral Register Agreement. Nothing in this document can be executed against a register that has none: the projection has no permitted-predicate set to test against, the channel has no construction, the encryption has no key, and the Per-Register Claim Projection has no Bilateral-Register-Agreement Hash to carry. This section is where the obligations that other sections place on an Agreement are gathered, and it is the definition of the Agreement Hash.

Declared items Each Bilateral Register Agreement MUST declare each of the following, save where an item is marked OPTIONAL or the text of the item admits its absence; lists which those are. The numbering is normative: it is the order in which the Agreement Hash of is computed, and it is the only order this document specifies.

1. The permitted-predicate set of .
2. The supported cryptographic primitives, including any post-quantum primitives selected under . Every primitive appearing in an equivalence list of item 3 MUST appear here.
3. The Cryptographic-Primitive-Upgrade Path of .
4. The transport, endpoint, framing and encryption construction of the bilateral channel of .
5. The regulator-identity-provider trust anchor of .
6. The notification endpoint of .
7. The statutory-regulator-access scope of , together with the per-jurisdiction permitted-read-field and permitted-read-predicate sets it is computed from.
8. The Subject Reference form of .
9. The Freshness Window of .
10. The register's data-format profile under , together with every value that profile obliges a declaring Agreement to supply or to name, in the order the profile enumerates them. A vocabulary release a profile requires the Agreement to name is such a value and is not a parameter in the sense of , so naming only the parameters would leave it outside the Agreement Hash.
11. The register's public key material, as a COSE Key Set carrying at least one claim-encryption key and at least one partial-attestation-signature key, each with its arp-key-status and arp-key-validity.
12. The response window after which a register is recorded unresponsive.
13. The per-principal per-subject query budget of and the interval over which it is measured.
14. Any per-subject ceiling under .
15. The ledger-head notarisation interval of .
16. The Transparency Service of .
17. The artefact retention period of .
18. The read rate limit of .
19. The notarisation polling bound of .
20. The authority origin of the reconciliation server the Agreement authorises.
21. At least one Audit Identity under .
22. The Register Operator's own read key.
23. Whether the Per-Register Claim Projection must carry the Requester-Binding Class.
24. The audit right over the query-budget counter of .
25. The reserved proportion of any per-subject ceiling and its per-principal sub-budget.
26. The response freshness tolerance of , which is the backward bound only. It MUST be at least sixty seconds, and MUST NOT exceed the effective ledger-head notarisation interval of or sixty seconds, whichever is longer, that interval being the shortest item 15 any Bilateral Register Agreement the deployment holds declares. The floor is stated because the bound runs backward from the reader's receipt of the response and the response was produced before that instant: a tolerance below the transit and clock disagreement between the two parties rejects every honest response, and a tolerance of zero rejects all of them, which is a denial of service a deployment can declare itself into without any party misbehaving. Sixty seconds is the figure this document fixes for the forward bound of this test and of the two others that bound a party against another's clock over a message it has just received, so using it as the floor makes the narrowest admissible interval symmetric. A fourth test, the witness observation window of , bounds a pair of clocks over an artefact published on an interval rather than over a message in flight; its forward bound is the greater of sixty seconds and twice that interval, and sixty seconds is its floor in both directions for the reason it is the floor here. The forward bound is that fixed sixty seconds and is not negotiable per Agreement: a forward bound each deployment set for itself would restore the untestable case the fixed one exists to close. Bounding the ceiling against this Agreement's own item 15 would admit a tolerance longer than the interval the deployment notarises at, and so a response naming a head the reader could already know to be superseded. Where that interval is itself shorter than sixty seconds the floor governs, a ceiling below a floor being a term no deployment can declare, and such a deployment trades the supersession property for liveness knowingly: it notarises more often than the window in which a reader will accept a response, so a response naming a superseded head is admissible by exactly the difference. A deployment that wants both notarises no more often than sixty seconds.
27. The Witness Set of , which MAY be empty.
28. The Witness Quorum of .
29. OPTIONALLY, an audience constraint under .
30. The regulator read keys of , or the means by which they are resolved from the trust anchor of item 5, together with the means by which key material for items 21, 22, 27 and 30 is retrieved. A Witness Entry carries a key thumbprint, and a thumbprint is not key material, so without this a relying party holding a Head Consistency Statement has no defined way to obtain the key that verifies it.
31. Whether partial attestations may be re-invoked under .
32. Whether the Register Operator notifies corrections to records it has attested, and the endpoint at which it does so, which is what makes the register-record-correction trigger of reachable.
33. The Coverage Probe allowance of : the number of probes an Audit Identity may commission against that register per interval, and the interval, as a two-element array of unsigned integers.

Items 26, 27, 28, 30, 31, 32 and 33 are new in this revision; item 29 is carried from -03 in a new position. Three of the seven, items 26, 30 and 31, were already relied on elsewhere in this document while sitting outside the Agreement Hash. obliges a deployment to declare a response freshness tolerance in its Bilateral Register Agreements; that is item 26. obliges an Agreement to declare the keys under which a regulator reads, and item 5's regulator-identity-provider trust anchor is not a key; that is item 30. In both cases two deployments could agree on every item the Agreement Hash committed to, differ on the term, and compute the same Agreement Hash -- an Agreement Hash that does not cover a term the Agreement is required to carry. makes re-invocation of partial attestations conditional on what the applicable Agreements permit without making that permission a declared item; that is item 31. Items 27 and 28 specify the witness quorum names and earlier revisions declined to fix. Items 32 and 33 are terms this revision creates rather than terms it moves inside the Agreement Hash: item 32 is what makes the register-record-correction trigger of reachable, and item 33 is the probe allowance meters against. An Agreement computed under an earlier revision does not compute the same Agreement Hash under this one. The Agreement Hash covers seven items it did not cover before -- 26, 27, 28, 30, 31, 32 and 33 -- and now fixes the CBOR type of every item and the ordering within every set-valued one, so the value changes for every Agreement even where no negotiated term has changed. Agreements MUST be recomputed, and a deployment holding a Bilateral-Register-Agreement Hash recorded before this revision MUST treat it as naming an Agreement under the earlier item list rather than as a value comparable with one computed under this section. Comparing the two is the Bilateral-Register-Agreement drift of , and a deployment that does not recompute will observe drift where none exists.

Witness Set and Witness Quorum establishes that an empty result is falsifiable to the extent that its reader holds head-consistency evidence for the served chain from an observer independent of the responding service, and that head evidence obtained only from that service bounds nothing. It states the preference -- a witness countersignature over the head, or, failing that, an independently anchored head digest -- without saying how many countersignatures, from whom, or what makes two of them two rather than one. This section says.

Witness Entries A Witness Set is a set of zero or more Witness Entries. Each Witness Entry is a CBOR array of exactly three elements, in this order and not nested:

1. the Audience Member Identifier, as defines it;
2. the Verification Method Reference, as defines it; and
3. an Operating-Party Identifier: an Authority Origin naming the party that controls the witness.

encodes those first two as a two-element array. Here they are the first and second elements of a three-element array and are not wrapped in one, because a Witness Entry is carried both in the Agreement Hash of and in the Policy Parameters Document of , and two readings of one shape would let those two artefacts disagree about a set they are both supposed to describe. Two Operating-Party Identifiers are distinct where they differ after normalisation under Sections 6.2.2 and 6.2.3 of . Comparison is over the normalised form and is otherwise bytewise. Without a stated normalisation https://acme.example and https://ACME.example/ are distinct to one implementation and identical to another, and whether a quorum is met turns on which. A Witness Entry's Operating-Party Identifier MUST NOT be that of the reconciliation server, of the Transparency Service of , of any party controlling either, of any party controlled by either, or of any party under common control with either, and no two Witness Entries counted toward one quorum may be under common control with each other. The first exclusion runs in every direction because running it upward alone excludes nothing that matters: a reconciliation server that incorporates three subsidiaries, declares three distinct Operating-Party Identifiers and satisfies a quorum of three controls every observation the quorum is composed of, and the fork is concerned with stays invisible while the quorum reports it as checked. The second exclusion is there because the rationale of this section is observer diversity and not identifier diversity: three witnesses that are three subsidiaries of one unrelated parent declare three distinct Operating-Party Identifiers, pass the distinctness test as a verifier computes it, and are one observation reported three times. The Register Operator of the addressed register, and any operator of a secondary store under , are excluded on the same ground.

Head Consistency Statements A Head Consistency Statement is a COSE_Sign1 by a witness, under the media type registered in , carrying the arp-witness-identifier header parameter registered in in its protected header, whose payload is the deterministically encoded CBOR array, under , of:

1. the text string arp-head-consistency-v1;
2. the Entry Sequence Number of the head covered;
3. the Self-Entry Hash of that entry;
4. the Statement Timestamp of the Ledger Head Statement the witness observed, in the form of ; and
5. the Witness Observation Time, being the time the witness produced this Statement, in the same form.

Item 5 exists because a COSE_Sign1 is not dateable from its own bytes, so a freshness rule over a Statement carrying no time is a rule no verifier can apply. adds a Statement Timestamp to the Ledger Head Statement for the same reason.

Witness Linkage Segments A Witness Linkage Segment is a COSE_Sign1 by a witness, under the media type registered in , carrying the arp-witness-identifier header parameter registered in in its protected header, whose payload is the deterministically encoded CBOR array, under , of:

1. the text string arp-witness-linkage-v1;
2. the Authority Origin of the reconciliation server whose Settlement-Layer Ledger the Segment covers, as a text string, normalised as normalises an Operating-Party Identifier, so that equality is a test a verifier computes rather than one it decides and a Segment cannot be presented as evidence about a Ledger it was not taken over;
3. the Entry Sequence Number of the lowest entry the Segment covers, as an unsigned integer;
4. the Entry Sequence Number of the highest entry it covers, as an unsigned integer;
5. the ordered array, lowest Entry Sequence Number first, of the linkage array of for each entry in that inclusive interval, each a four-element array of the Entry Sequence Number as an unsigned integer and the Prior-Entry Hash, the Self-Entry Hash and the Signing Input Digest of that entry's Entry Signature, each as a byte string; and
6. the time the witness produced this Segment, in the form of . It is present for the reason item 5 of is present: a COSE_Sign1 is not dateable from its own bytes.

A Segment MUST cover at least one and at most one thousand entries. The cap is what makes the artefact bounded independently of how often a witness observes or how fast a Ledger is appended to, both of which this document leaves to a deployment; a witness with more entries to cover publishes consecutive Segments rather than one larger one. A Witness Entry names one Ledger. A party observing more than one MUST appear as one Witness Entry per Ledger, under a distinct Operating-Party Identifier and so a distinct Authority Origin, because the addressing below is by Entry Sequence Number alone and two series on one origin would give one sequence number two Segments and no conforming answer. Item 3 of a Segment MUST be one greater than item 4 of the Segment the witness published before it, or, in the first Segment it publishes for a Ledger, the Entry Sequence Number the witness elects to attest from. The lowest entry a witness's first Segment for a Ledger covers is that witness's Attestation Floor for it, and a witness chooses that value when it begins publishing: one that begins observing a Ledger at entry n attests from n and makes no claim below it, which is what lets a witness join a Ledger of any length without signing its history. A witness MUST publish Segments that together cover every Entry Sequence Number from its Attestation Floor to the head named by the most recent Head Consistency Statement it has published for that Ledger. The obligation is stated as coverage rather than per observation so that an interval in which nothing was appended obliges nothing: republishes the Ledger Head Statement once per notarisation interval and not on every append, and a Statement covering a head already covered needs no further Segment. A Statement whose head the witness's Segments do not reach is a Statement no relying party can use for the second branch of ; the first branch needs no Segment. A witness MUST serve, at /.well-known/arp-witness-linkage/{n} on the Authority Origin of its Operating-Party Identifier, where {n} is an Entry Sequence Number, the single Segment whose interval contains n, and MUST answer 404 where it has published none covering n, which is the answer for every n below its Attestation Floor. It MUST serve its most recently published Segment at /.well-known/arp-witness-linkage. Each response carries exactly one Segment under the media type registered in . A witness MUST serve the same Segment for a given Entry Sequence Number on every request, and MUST serve Segments to any party without authentication, for the reason gives for serving Head Consistency Statements that way: an artefact obtainable only through the party it is evidence about is that party's selection. A relying party assembles an interval by requesting the Segment containing the head a response names and then the Segment containing one above each Segment's item 4, until one covers the head a Head Consistency Statement names. It MUST stop and treat the interval as uncovered on a 404, on a Segment whose item 3 is not one greater than the item 4 of the Segment below it, or on a Segment carrying a signature that does not verify. The first Segment it fetches has no Segment below it and is subject only to the last of those. Addressing per entry rather than per collection is what makes the cost of assembling an interval proportional to the interval rather than to the witness's publication history; the interval itself is unbounded, so a relying party MAY decline to assemble one longer than it is prepared to fetch and holds no evidence from that witness where it does. A witness MUST retain and serve every Segment it has published for a Ledger for as long as it publishes Segments for that Ledger, and for at least one year after its last publication for it. The period is stated against the witness's own publication history because a witness is party to no Bilateral Register Agreement and cannot compute the retention period of . A relying party that cannot obtain the Segments covering an interval holds no evidence for that interval from that witness, which is the same outcome as an unreachable origin. Two Segments by one witness for one Ledger whose intervals intersect, and whose linkage arrays differ at any entry in the intersection, are a witness equivocation. A relying party holding both MUST NOT count that witness toward a quorum under . Detection is opportunistic in the way says detection of two entries at one Entry Sequence Number is opportunistic: the addressing above returns one Segment per entry, so a party sees a pair only where it retained an earlier Segment, or compared with another party, and no single request reveals one. What the rules above establish is not that equivocation is caught but that it is the only way a witness can present two chains over one interval, since a conforming witness publishes each interval once and serves one Segment for each entry. That is the property the append-only claim of rests on, and its enforcement is an audit obligation rather than a verifier-side test. A Segment carries no Reconciliation Hash, no Claim Hash and no structural metadata, because a linkage array carries none. What its unauthenticated publication adds over the entitled read of is set out in .

The quorum rule The Witness Quorum is an integer t with 0 <= t <= n, where n is the cardinality of the Witness Set. A Witness Set MUST contain at least t entries with pairwise distinct Operating-Party Identifiers; an Agreement whose Witness Set does not is non-conforming, and a deployment MUST NOT address a register under it. Without that constraint an Agreement declaring three entries under one operating party and t of three is well formed, satisfiable by nobody, and every empty result served under it is permanently unfalsifiable with no conformance test firing. A relying party holds sufficient head-consistency evidence for an empty result under when it holds Head Consistency Statements from at least t Witness Entries where:

• each verifies under the key material declared for that entry;
• the t entries have pairwise distinct Operating-Party Identifiers;
• the t entries have pairwise distinct Verification Method References, and a relying party MUST reject a set in which two entries resolve to the same key. Distinctness of the Operating-Party Identifier alone does not establish that two entries are two observations: two entries declaring one key under two Operating-Party Identifiers are satisfied by a single COSE_Sign1, and a relying party applying only the previous condition counts one signature twice and reports a quorum of two met by one signer. That failure is mechanical and locally checkable, which distinguishes it from the declared-independence limit concedes and cannot close: a verifier cannot test whether two named parties are truly independent, and it can always test whether two entries name one key;
• each covers the head the response names, that is, item 2 of the Statement equals the response's as-of-sequence-number and item 3 equals the Self-Entry Hash that response names; or covers a head at a higher Entry Sequence Number and the relying party additionally holds the Witness Linkage Segments of covering the two, obtained from that witness's own origin and not from the responding service, and has verified all six of:
  1. that each Segment verifies under the same key material as the Statement, carries the same arp-witness-identifier, and carries as its item 6 a time no later than the Witness Observation Time of that Statement, so that the chain and the head are one witness's observation, not two parties', and not one witness's later account of an earlier interval;
  2. that item 2 of each names the Authority Origin of the responding reconciliation server;
  3. that item 3 of each Segment above the lowest it holds is one greater than item 4 of the Segment below it, and that between them they cover every Entry Sequence Number from the named head to the head the Statement covers, inclusive. A span covered by one Segment satisfies this on its second clause alone;
  4. that the Self-Entry Hash of the linkage array at the Statement's Entry Sequence Number equals item 3 of that Statement;
  5. that the Self-Entry Hash of the linkage array at the named head equals the one the response names; and
  6. that the linkage array at each sequence number in that interval above the named head carries, as its Prior-Entry Hash, the Signing Input Digest that the linkage array of the entry below it reports. The named head is the bottom of the interval, the entry below it is outside the Statement's coverage, and check 5 is what pins that end.
  A relying party holding two Segments from one witness that equivocate under MUST NOT count that witness toward the quorum, whichever branch it would otherwise satisfy. The linkage array carries that digest as its fourth element precisely so this condition is computable by the party required to compute it: a Signing Input Digest is taken over the Sig_structure, so neither the protected header nor the payload of the entry below is recoverable from a sequence number and three hashes, and the substitution a reader might reach for instead is the one the next sentence forbids. Those last two values are digests over different preimages -- takes a Self-Entry Hash over the entry array with two positions nulled and a Prior-Entry Hash over a Sig_structure -- so a verifier MUST NOT test them for equality against each other; and
• each carries a Witness Observation Time no earlier than sixty seconds before the Statement Timestamp of item 4 and no later than the greater of sixty seconds and twice the effective ledger-head notarisation interval after it, that interval being the shortest any Bilateral Register Agreement the deployment holds declares, per the direction rule of . The sixty seconds is the allowance this document makes wherever one party's clock is tested against another's, here the witness's against the reconciliation server's: with no allowance a witness whose clock is a second slow fails this condition on every Statement it publishes, permanently and with no party misbehaving, which is the case item 26 of floors the response freshness tolerance to avoid. The forward bound is floored for the same reason: a deployment notarising every few seconds would otherwise admit a window of a few seconds against a clock this document does not synchronise, and a witness running slightly fast would fail on every Statement it published. gathers the clock bounds this document sets. A witness whose Statements fall outside this window satisfies no condition of this rule and so counts toward no quorum, which is the outcome gathers for every other way a witness can fail to contribute.

A witness MUST publish its Head Consistency Statements at /.well-known/arp-head-consistency on the Authority Origin of its Operating-Party Identifier, most recent first, under the media type registered in , and MUST serve them to any party without authentication. The Operating-Party Identifier is for this reason an Authority Origin and not a bare name: an identifier that names a party without locating it cannot be the route by which the artefact is obtained. A relying party MUST obtain Head Consistency Statements from the witnesses' own origins, and MUST NOT accept for quorum purposes a Statement obtained from the responding service. Until this revision the document specified the artefact, the quorum arithmetic and the freshness window, and specified no channel at all, which left the obvious implementation: the responding service hands over the witness statements alongside its response. That implementation satisfies every condition above. The witness signature stops the service forging a Statement and does nothing to stop it choosing which ones to pass on, and under exactly the fork this mechanism exists to detect, an operator serving two branches hands each reader the statements of the witnesses it fed that branch. Every check passes on both branches and the quorum is met on both. This is the whole of the artefact's value and it was the one thing not stated. A Head Consistency Statement obtained from the party it is evidence about is not independent evidence; it is the responding service's own selection, countersigned. Where a witness origin is unreachable, the relying party holds fewer than t Statements and MUST act under accordingly, rather than accepting a substitute from the service. The chain requirement is what makes the artefact worth its name, and the requirement that the Segments come from the witness is what makes the chain evidence. A witness signature over a head at a higher sequence number is, on its own, evidence about whatever branch that witness was served, which may not be the reader's: a fork at disjoint sequence numbers is precisely a pair of heads neither of which contradicts the other. So the two observations have to be put on one chain, and the chain has to be one the responding service did not write. Anchoring the ends of a service-supplied chain does not do it, and the arithmetic is worth stating because it is not obvious. The condition anchors two Self-Entry Hashes, one signed by the witness at the top of the span and one named by the response at the bottom, and then walks a chain over two other positions, the Prior-Entry Hash and the Signing Input Digest. No anchored value sits in a position the chain reads. The reader cannot recompute any value it does read, for the reason the previous paragraph gives. And the lower anchor is the response's own claim, so it constrains the service against itself and nothing else. A service supplying the arrays therefore supplies every value the chain is made of, and an equality between two values one party supplies is not evidence about that party: it can serve the Self-Entry Hash the witness published at the top, its own values in every other position, and satisfy each part of the condition. Extending the span makes that easier rather than harder, since every interior array is two further values the condition constrains only against their neighbours. Anchoring both ends does better and does not reach. Where the lower anchor is a value in a position the chain reads and comes from somewhere other than the responding service, the chain values of a three-array span are determined, and only those: the interior Self-Entry Hash is constrained by neither anchor nor chain even there. A span of four is not: the two arrays between the ends are constrained only against each other, and every further entry adds another such pair. The condition places no bound on the span, and the span is the distance between a head a witness happened to observe and a head a response happens to name, so it is not a quantity the relying party controls. Segments served by the witness bound the freedom by a different route: every value the chain is made of was observed and signed by a party that is not the one being checked, the covering requirement of leaves no Entry Sequence Number in the interval that a service supplies, and the two anchors become checks that the witness's chain is the one the Statement and the response are about. What that buys and where the residue is. A witness reads the Ledger from the reconciliation server, so a witness is not an independent observer of the entries; it is an independent recorder of what it was served, at a time it stamps and under a signature it cannot revise. The property the Segments deliver is therefore append-only rather than absolute: a conforming witness publishes each interval once and serves one Segment per entry, so an operator rewriting an interval that witness has covered can only do so with a witness that equivocates, and states both what that costs the witness and why detecting it is opportunistic rather than a verifier-side test. An operator that rewrites an interval before any witness has covered it, or that serves a rewritten chain to a witness setting its Attestation Floor above the rewrite, obtains a witness-signed chain over the rewrite. What bounds that is witness diversity and observation frequency, both of which the Witness Set and the notarisation interval already govern, and it is the same residue concedes for declared independence rather than a new one. A Statement covering the named head exactly needs no Segment, because there is nothing to link. The window in the fifth condition is measured from the Statement Timestamp of the Ledger Head Statement and not from the Entry Timestamp of the head, and it is two intervals and not one, because republishes the Ledger Head Statement once per notarisation interval and not on every append. An entry appended just after a publication is not published until one interval later; a window of one interval measured from that entry's own timestamp is already closed when the witness first sees the head, and no conforming Statement could exist for it. The distinctness requirement is the substance of the rule. Countersignatures from witnesses under one operating party are one observation reported t times, and a quorum satisfied by them is a quorum in arithmetic only: the equivocation is concerned with becomes observable when two independent observers compare heads, and two instances of one observer are not two observers.

Discovery A relying party is not a party to any Bilateral Register Agreement and holds only the hashes of those Agreements, so a quorum declared only inside an Agreement is a test the party required to run it cannot read. The Policy Parameters Document of therefore carries the effective Witness Set and the effective Witness Quorum, and a relying party evaluates the quorum against that document. Where a deployment holds more than one Bilateral Register Agreement, the effective Witness Set is the intersection of the Witness Sets every such Agreement declares and the effective Witness Quorum is the largest any of them declares, per the direction rule of . Two Witness Entries are equal for the purpose of that intersection when their Operating-Party Identifiers are equal and their Verification Method References are equal, and the intersection carries, for each such pair, the entry as the Agreement with the lexicographically least Agreement Hash declares it. Stating the relation is not pedantry. Taken over whole entries, the intersection empties on any difference in the first element -- an Audience Member Identifier written two ways for one witness -- and this section then obliges a conforming deployment to stop serving reads entirely. Taken over the Operating-Party Identifier alone, two entries declaring different keys for one party merge, and a relying party accepts a Head Consistency Statement under key material only one of the two Agreements declared. Both readings are available from the bare word "intersection", one produces an outage and the other produces an unauthorised key, and a deployment cannot be conforming under both. The effective Witness Set MUST contain at least the effective Witness Quorum entries with pairwise distinct Operating-Party Identifiers. Where it does not, the deployment is non-conforming and MUST NOT serve reads under . The per-Agreement constraint of does not reach this: two Agreements each declaring two entries and a quorum of two, with no entry in common, are each conforming and together produce an empty effective set under a quorum of two, which is the unsatisfiable quorum that constraint exists to forbid.

Where the quorum is zero A Witness Quorum of 0, which a Witness Set of zero entries requires, declares that no witness evidence is available. A relying party acting on an empty result served under an effective quorum of 0 SHOULD instead hold an independently anchored head digest as provides, and MUST NOT treat the absence of a witness requirement as evidence that the head is uncontradicted. A deployment declaring 0 is making a statement about what its empty results can be checked against, in a term a relying party can read, rather than leaving a reader to infer it.

The Agreement Hash Each Bilateral Register Agreement carries an Agreement Hash: the SHA-256 digest over the deterministically encoded CBOR array, under , of the items of in the order given there. The array has exactly thirty-three elements. The reconciliation server and the Register Operator compute it independently and MUST obtain the same value. Determinism under Section 4.2.1 of fixes how a given value is encoded. It does not fix which CBOR type an item takes, nor the order of elements within an item that is a set, and two parties that differ on either compute different digests from identical negotiated terms. Since suspends reconciliation on a deviation, that is an outage and not a warning. The types are therefore fixed here.

Item	CBOR encoding
1, 2, 21, 27, 30	array, sorted in bytewise lexicographic order of the deterministic CBOR encoding of each element
3	three-element array, in the class order of , each element that class's equivalence list in the declared preference order and not sorted
4	four-element array: transport identifier, endpoint URI and framing identifier, each a text string, and the sorted array of COSE algorithm identifiers of the encryption construction
5, 8, 16, 20	text string
6	URI, as a text string
7	three-element array: the statutory-regulator-access scope as a text string, and the per-jurisdiction permitted-read-field and permitted-read-predicate sets, each a sorted array of two-element arrays of the jurisdiction identifier and the sorted set for it
9, 12, 15, 17, 19, 26	unsigned integer, seconds
10	two-element array: the profile identifier as a text string, and the array of profile-obliged values in the order that profile enumerates them
11, 22	COSE Key Set, its keys sorted in bytewise lexicographic order of the deterministic CBOR encoding of each key
13	two-element array: the budget as an unsigned integer count, and the interval in seconds as an unsigned integer
14, 28	unsigned integer
18	two-element array: the permitted request count as an unsigned integer, and the interval in seconds as an unsigned integer
23, 24, 31	boolean
32	two-element array: a boolean, and the endpoint URI as a text string or null
33	two-element array of unsigned integers: the probe allowance and the interval in seconds
25	two-element array: the reserved proportion as a CBOR decimal fraction, and the per-principal sub-budget as an unsigned integer
29	two-element array: the maximum cardinality as an unsigned integer or null, and the permitted member class as a text string or null

Every item that is a set is encoded as a CBOR array sorted in bytewise lexicographic order of the deterministic CBOR encoding of each element. This document already requires that ordering of the Audience Set, of the algorithm array of and of the origin array of , and for the same reason: an unordered set gives one Agreement as many hashes as it has permutations. Items 3 and 10 are the exceptions and are called out in the table as such, because each is a sequence rather than a set: declares an ordered equivalence list whose order is the preference, and item 10 takes its order from the profile that enumerates the values. Sorting either would discard the meaning it carries, and a change of order in either would then leave the Agreement Hash unmoved. An item that is absent, inapplicable or empty is encoded as CBOR null, and the element is present in the array regardless. Items 14, 25, 27 and 29 are the only items that may be absent: 14 and 25 where the Agreement sets no per-subject ceiling, 27 where the Witness Set is empty, and 29 because it is OPTIONAL. Item 25 is null whenever item 14 is. An empty Witness Set is encoded as CBOR null and not as an empty array. Every other item MUST be present and MUST NOT be null. Encoding an absent per-subject ceiling as null, as zero, or by omitting the element are three readings of one sentence, and all three produce different Agreement Hashes. The order is fixed by the numbering of and by nothing else. An implementation MUST NOT derive it from the order in which terms appear in the negotiated instrument, from any serialisation the parties exchange, or from an alphabetisation of the item names. Earlier revisions of this document specified the digest over "its canonicalised content", which named no order and so did not make independent computation of one value possible. A change to any item changes the Agreement Hash, and suspends reconciliation against a register whose Agreement Hash deviates from the one committed at the start of a reconciliation event. Items 11, 22, 27 and 30 carry key material and witness membership, which change under ordinary operation -- a rotation under the upgrade path of item 3, the addition of a witness -- so an Agreement Hash change is a renegotiation event and the parties MUST agree the new Agreement Hash before the operation that causes it. A deployment that rotates first and renegotiates afterwards has suspended its own reconciliation, by its own drift rule, at the moment its upgrade path was exercised.

What a Bilateral Register Agreement does not establish An Agreement is a declaration by two parties. It is not evidence that what it declares is true. The Operating-Party Identifiers of are declared, not proven. excludes a witness under the control of the responding service, under common control with it, or controlling it, and that exclusion is normative; what this document supplies no mechanism for is detecting a false declaration. Two witnesses under common control that each declare a distinct Operating-Party Identifier satisfy the distinctness test as a verifier can compute it, and a relying party comparing the two identifiers sees two parties. The requirement is worth stating regardless, because a party that declares an independence it does not have has made a false attributable claim rather than benefited from an unexamined silence, and because an Audit Identity under can be given the Witness Set to examine. But a relying party MUST NOT treat a met quorum as proof of observer diversity. It is proof that observer diversity was declared, by a named party, in a term that party can be held to. The same holds of item 20, the Authority Origin, which already requires a register operator to corroborate by publishing an Authorised-Origin Document, and which is the one declared item this document does provide a mechanism to check.

Aggregate Statements Nothing above governs what may be said about a set of Reconciliation Outputs. That is the gap through which a four-valued vocabulary becomes a percentage. forbids the Verdict Arithmetic from combining a Non-Answer Reason, and requires an indeterminate contribution to propagate rather than be resolved. Both hold inside one reconciliation. Neither reaches the report that says a deployment ran at ninety-one per cent. The prohibition is a rule addressed to an implementer, and the pressure to state a single figure arrives from outside engineering, after the vocabulary is public and looks like a scoring system. A rule is what an engineer follows and a structure is what a spreadsheet cannot get around, and only the second survives that pressure. An Aggregate Statement is the only form in which this document permits a count, rate or proportion over more than one Reconciliation Output to be published, cited, or supplied under or . It is a COSE_Sign1 by the reconciliation-server sealing key whose payload comprises:

• the Declared Population: the criterion by which an Output is in the set, and the Basis on which it is decided, being one of catalogue where the population is a list held before the period began, enumeration where it is everything in a stated Entry Sequence Number range, or declared where the operator asserts it and nothing else fixes it
• where the Basis is enumeration, the Entry Sequence Number range, so that the denominator is checkable against the Ledger as checks a sweep
• the Denominator: the count of Outputs in the Declared Population
• the Verdict Vector: one count for each value of the Combined Verdict, including indeterminate, in the order gives
• the Non-Answer Vector: one count for each Non-Answer Reason in the registry of that appears in the set, each naming its reason
• a Statement Timestamp, a Sealing-Key Identifier and a signature

The Verdict Vector and the Non-Answer Vector MUST sum to the Denominator, and a reader MUST reject an Aggregate Statement in which they do not. That sentence is the mechanism and everything else is scaffolding for it. A component of a sum that has to balance cannot be averaged away, folded into a neighbour, or dropped from a denominator, because each of those breaks the arithmetic in a way any reader can see without holding a single Output. There is no representation of this Statement in which indeterminate is absent and the numbers still add up. Compare the rule it replaces, which said an implementation must not combine certain values: an implementation that combined them anyway produced a document indistinguishable from one that had not. A deployment MAY publish a rate derived from an Aggregate Statement, and where it does it MUST publish the Statement alongside and MUST NOT publish a derived figure alone. A rate is a projection of the vector onto one number, and this document does not forbid the projection. It requires that the thing projected from travels with it, so that a reader who wants to know what the other nine per cent were is one artefact away rather than dependent on the publisher's goodwill. Why the Basis is declared and not assumed. A proportion is a claim about a denominator, and a denominator no one stated is a denominator the publisher chose after seeing the numerator. enumeration is the strong case and is checkable against the Ledger by anyone. catalogue is weaker and still falsifiable, since the list existed before the period. declared is the operator's assertion, is not falsifiable, and MUST be recorded as such rather than presented as though it were either of the others. The three-way distinction, and the requirement that a report account for every unit it did not examine rather than reconcile by arithmetic, are taken from the Coverage Attestation Profile , which specifies them in a form that is not particular to this protocol. What this does not do. It does not stop a party outside the protocol computing whatever it likes from Outputs it holds. Nothing can. What it stops is that party doing so and citing this document, because a figure published without its Statement is non-conforming and a figure published with one carries its own contradiction where it has one. The distinction between a number nobody can check and a number whose components must balance is not enforcement, it is the difference between a claim that has to be believed and a claim that can be refused. Acknowledged. The general problem, and the observation that a prohibition on averaging is not a mechanism, are Emek Can Dogru's, put to the SCITT mailing list on 20 August 2026.

Agentic Principal Reconciliation The Agent Friend-or-Foe Determination described in the Requester Identity Binding and Agent Friend-or-Foe Gate above establishes whether the requester of a reconciliation is friendly. ARP additionally supports reconciling an agent's principal binding as the subject of a reconciliation in its own right, so that the question "does a real, authenticated principal stand behind this agent?" can itself be answered against authoritative identity registers rather than asserted. A reconciliation over the agent: predicate branch takes as its Subject Identifier the agent's declared identity (for example its signature-agent-card key thumbprint or a directory identifier) and as its Attested Value the principal binding the agent asserts. Addressed registers for this predicate class are identity and credential registers -- for example an organisational directory, a credential-issuer status list, or a national identity register -- each under its own Bilateral Register Agreement. The Combined Verdict answers whether the asserted principal binding is corroborated:

• match: the agent's asserted principal binding is corroborated by the addressed registers; the agent is FRIENDLY with an attributable principal.
• no-match with divergence axis agent-impersonation-suspected: the asserted binding is contradicted; the agent is asserting a principal it is not bound to.
• no-match with divergence axis agent-credential-absent or agent-principal-unverifiable: no corroborating record exists; the binding cannot be established and the agent MUST be treated as ENEMY.

This composition allows a relying party to gate an action not merely on the presence of an agent signature but on register-corroborated proof that an accountable principal stands behind it, narrowing the impersonation surface at the reconciliation layer. The result is a Reconciliation Output like any other: sealed against a Policy-Version Hash, written to the Settlement-Layer Ledger without claim or register content, and re-evaluable if the underlying credential is later revoked.

Encoding

CBOR-COSE Encoding The mandatory-to-implement encoding for ARP messages on the wire is CBOR with COSE envelopes. COSE_Sign1 is used for both Partial Attestations and the Sealing Signature. Every COSE_Sign1 this document defines MUST carry the algorithm identifier (label 1) and the key identifier (label 4) in its protected header, and MUST NOT carry either in an unprotected header. A Signing Input Digest under depends on the protected header and on nothing else in the envelope, so an algorithm or key identifier placed outside it is a value that digest does not bind -- and relies on the algorithm identifier being bound. The protected header of a Partial Attestation and of a sealed Reconciliation Output MUST additionally include the Bilateral-Register-Agreement Hash and Policy-Version Hash as COSE header parameters; the other COSE_Sign1 structures this document defines carry the headers their own sections state registered per . arp-bilateral-agreement-hash always carries an array, sorted in lexicographic byte order: a Partial Attestation's array has exactly one member, and a Sealing Signature's has one per addressed register. A single encoding for both avoids a decoder having to infer the type from context. Pending registration, implementations MAY use labels from the private-use range of the COSE Header Parameters registry; such use is not interoperable. Every digest this document takes over a CBOR encoding is taken under the Core Deterministic Encoding Requirements of Section 4.2.1 of , and this document cites that section rather than the word canonical because the two name different things. Section 4.2.1 orders the pairs of a map in the bytewise lexicographic order of the deterministic encodings of the keys. Section 4.2.3 of the same document describes a Length-First Map Key Ordering, in which a shorter encoded key sorts ahead of a longer one and ties are broken bytewise, and that is what several widely used CBOR libraries produce under an option named canonical, the name the length-first rule carried before separated the two. An implementation MUST produce the ordering of Section 4.2.1. A library option named canonical commonly produces Section 4.2.3 instead, and an implementation that relies on one without establishing which it produces has not met that requirement. The two orderings agree for any map whose keys are integers or strings and share a CBOR major type, at any mix of lengths: for those types the head byte never decreases as the encoding lengthens, and where two keys share a head byte the bytewise comparison continues into the bytes that follow it, which orders them the same way. The head byte of an array, a map or a tag encodes a count rather than a length, and the agreement does not hold there; COSE admits only integer and string labels, so no map on a digest path in this document has a key of those types. Integers span two major types, so a header pairing a positive label with a negative one is outside the agreement, and that is the case the next paragraph is about. They diverge only where a map mixes major types and the key of the higher major type has the strictly shorter encoding. A negative label of -1 is the single byte 0x20; a label of 256 is 0x19 and two further bytes. Length-first puts -1 first; bytewise puts 256 first, 0x19 being below 0x20. No protected header this document specifies reaches that case. The headers it defines carry the algorithm identifier, the key identifier and the parameters registers, and a map of those sorts identically under both orderings. The requirement is stated so that it stays that way: permits labels from the private-use range pending registration, private-use labels are negative, and a deployment that pairs one with a registered label of 256 or above has built the divergent case out of two permitted choices. An implementation that produced Section 4.2.3 there would encode one protected header differently from one that produced Section 4.2.1, and so compute a different Signing Input Digest over one signing act and a different Prior-Entry Hash for the entry above it. The head comparison of treats that as a fork, against an operator that equivocated about nothing. The entry array of is an array and not a map for the reason that section gives, which places the ordering question at the protected headers and not at the entry.

Reconciliation Request Binding A reconciliation is commissioned by POST /arp/reconciliations on the reconciliation server's authority origin, with a request body carrying the Canonical Claim, the Audience Set the requester asks for, and, where the requester is an agent, its asserted principal. The body is CBOR under the media type registered in for a reconciliation request, save for the Canonical Claim, which is carried as a CBOR byte string holding the serialisation of the claim exactly as the Claim Hash is taken over it. Carrying the claim as native CBOR would need the CBOR-to-JSON mapping declines to define, and two servers receiving identical bytes would compute different Claim Hashes. The request MUST be signed under the profile of , with tag set to arp-reconcile. An Audience Member other than the Requesting Principal MUST have been enrolled at the reconciliation server before it may be named: an enrolment binds an accountable-principal identifier to a Verification Method Reference, is performed by the party being enrolled, and is out of scope for this document. A server MUST refuse to name an unenrolled member. Without enrolment a requester could name any identifier it liked, and the named party -- a competitor, a journalist, a foreign ministry -- would be handed a sealed, register-attested record that a named subject had been investigated under a named predicate, without its consent and without any register's. Naming is an assertion by the requester; enrolment is what makes it an assertion about a party that has agreed to receive. A refusal on that ground discloses that a named identifier is not enrolled, which a requester able to repeat it turns into an enumeration of the enrolment roster. A server MUST charge such a refusal against the requester's rate limit under and MUST record it in the access log that section requires. refuses to distinguish absence from inentitlement on the read path, on the ground that answering differently would turn every endpoint into an existence oracle; this endpoint is outside that section, so the principle is carried here by rate and by record rather than by collapsing the two answers, because a requester naming an audience member it believes enrolled needs to be told when it is wrong. The residual is recorded in . The response is one of four things, the fourth being the 401 of where the request's own signature was not accepted. A 200 whose body is the signed read response of , whose result element is the sealed Reconciliation Output and whose As-Of pair gives the Ledger head at the moment of delivery. That is the delivery requires, and it is what carries the Reconciliation Hash: the requester computes it over the Output it has just been handed, and the signed response fixes the head against which every later read of that Output is compared. A 422 carrying a Remediation Advisory, where the Adversarial Pre-Transmission Test did not emit a Pass and no override was authorised, or where a named regime is not one the policy-epoch store admits for the predicate, or where a named Audience Member is not enrolled. Or a 403 carrying a Remediation Advisory whose sole content is the Agent-IFF ground, where the Agent-IFF policy of the Requester Identity Binding and Agent Friend-or-Foe Gate section refuses the requester outright for the predicate class. Both refusals are signed as requires of a 4xx, so a refused requester holds evidence of what it asked and what it was told. A refusal under or an audience constraint under is not a fourth case: those refuse a register, and the reconciliation is sealed and delivered with the reason recorded against that register.

HTTP Message Signature Binding Where a reconciliation is requested over HTTP by an autonomous agent, the request MUST be signed under HTTP Message Signatures , with the signature-agent key resolvable through a Web Bot Auth signature-agent card , advertised via the Signature-Agent header , which also defines the key directory it names. The reconciliation server derives the Agent Friend-or-Foe Determination from verification of that signature and, where required by the Agent-IFF policy, a Verified Principal Credential carried in the request body.

Output and Ledger Read Binding This section is the wire binding for every read this document requires of a party outside the reconciliation server. Earlier revisions stated what a read returns and never how one is requested, which left every discovery path ending at a value its holder could not present to anything. Requests are HTTP over TLS to the reconciliation server's authority origin, the same origin whose Sealing-Key Identifier resolves under . Every hash appearing in a path segment is base64url-encoded without padding; every Authority Origin appearing in one is percent-encoded as Section 2.1 of provides; and every timestamp in a path or query parameter is in the form pins. The @target-uri is inside the request-binding digest of , so an encoding two implementations could choose differently would make their bindings differ over the same read. A non-Requesting Audience Member is not told that origin by this protocol; it learns it from the party that named it, and this document defines no directory by which a principal discovers the servers at which Outputs naming it may exist.

Request signing profile requires an application that uses it to state a profile. This is that profile. It governs every request to an operation of and the commissioning request of .

• Every request MUST carry exactly one signature, labelled arp.
• The covered components MUST be @method, @target-uri, and, where the request carries a body, content-digest as defines it, together with the signature parameters created, expires, nonce, keyid, alg and tag. A request covering fewer MUST be refused. tag is arp-read for an operation of and arp-reconcile for the commissioning request of ; those are the only two values, and a server MUST reject a request whose tag does not match the endpoint it was sent to.
• Covering content-digest is what binds the body. The commissioning request carries the Canonical Claim, the requested Audience Set and any asserted principal in its body; a signature that covered only the target would leave an intermediary free to substitute the subject or add Audience Members and have the result sealed, ledgered and notarised as the signed requester's.
• The nonce MUST be at least 128 bits drawn from a cryptographically secure random source, base64url-encoded.
• expires MUST be no more than 300 seconds after created. A server MUST reject a request whose created is more than 300 seconds in the past or more than 60 seconds in the future, and MUST reject a repeated nonce from the same keyid within that window. Without this a captured read request replays indefinitely, which closes only for requests that initiate a reconciliation.
• The permitted signature algorithms are those the deployment declares for the partial-attestation-signature class in its Cryptographic-Primitive-Upgrade Path, so that read authentication rotates with everything else.
• keyid MUST be the JWK thumbprint of the requester's public key, computed as in . For an Audience Member it MUST equal the Verification Method Reference the Output names. For a regulator, a Register Operator or an Audit Identity it MUST be a key the corresponding Bilateral Register Agreement declares. For a witness reading under it MUST be the thumbprint a Witness Entry of carries, in a Bilateral Register Agreement the deployment holds. For a requester commissioning a reconciliation it is the key that becomes that requester's Verification Method Reference in the resulting Audience Set. Key material is retrieved as that agreement provides, or, for an agent, through the Web Bot Auth directory of .
• The reconciliation server MUST publish a Policy Parameters Document at /.well-known/arp-policy-parameters on its Authority Origin: a COSE_Sign1 by its sealing key, under the media type registered in , whose payload is the six-element CBOR array of: a Publication Timestamp, in the form fixes; the array of permitted signature algorithm identifiers, sorted in bytewise lexicographic order of the deterministic CBOR encoding of each element; the array of per-predicate entries, each a four-element array of the predicate, the admitted regime set sorted in bytewise lexicographic order, the two-element array of the resolved Verdict Arithmetic and its parameters, and the reliance interval, the entries themselves sorted by predicate; and the array of two-element arrays of the identifier and effective time of every Pattern-Library and Policy-Version transition the server has applied, sorted by effective time, which relies on; and the two-element array of the effective Witness Set and the effective Witness Quorum of , the Witness Set sorted in bytewise lexicographic order of the deterministic CBOR encoding of each entry; and the two-element array of the response freshness tolerance of in seconds and the effective ledger-head notarisation interval that bounds it, each an unsigned integer. The sixth element is present for the same reason as the fifth. obliges every reader of a read response to check that the response time falls within an interval whose backward bound is a declared tolerance, and declares that tolerance in the Bilateral Register Agreements. The forward bound of that interval is the fixed sixty seconds of , which every reader already holds because this document states it, so it is the backward bound alone that has to be published here. A relying party is party to no Agreement and holds only their hashes, so the tolerance every reader must apply was readable only by the parties who did not have to apply it themselves, which is precisely the defect the Witness Set element was added to fix. Without that fifth element a relying party, which holds only Agreement Hashes, could not evaluate the quorum the same section obliges it to evaluate. The Publication Timestamp is first because the rest of the array is evidence about the reconciliation server, published by the reconciliation server, under its own key, and a COSE_Sign1 is not dateable from its own bytes. Two Documents published a year apart, one of which has had a transition or a Witness Entry quietly dropped from it, are otherwise indistinguishable to every party the Document exists to inform. This document already reached that conclusion twice, for the Ledger Head Statement of and for the Head Consistency Statement of , and the same reasoning was not carried here. The reconciliation server MUST submit each published Policy Parameters Document for notarisation by the Transparency Service of , under its own media type, within the ledger-head notarisation interval of that section measured from its Publication Timestamp, and MUST republish it on that interval whether or not its contents changed. A Document that changed without a new Publication Timestamp, or a published Document with no notarisation inside the interval, is non-conforming. The obligation to republish unchanged is what makes silence readable: without it, an operator that has removed a Witness Entry and an operator that has changed nothing publish the same thing, and the notarised series has no entry to be missing. A relying party MUST NOT treat a Policy Parameters Document as current where its Publication Timestamp is older than twice that interval, and MUST refuse to evaluate a quorum against one it cannot date. A requester is party to no Bilateral Register Agreement and could not otherwise determine how to sign, and publishing the resolved parameters removes the regime-shopping probe of by making its result available without probing.
• A request that is unsigned, that fails signature verification, that is outside the freshness window, or that replays a nonce MUST be refused with 401. A 401 is the one response of this section that is not signed under : its payload would have to bind a request carrying no nonce and no key identifier, and there is no requester key to bind it to. A 401 therefore carries no body, and a requester receiving one has learned only that its own signature was not accepted.

Read operations Nine operations are defined, and no read of an Output or of the Settlement-Layer Ledger by a party outside the reconciliation server is defined anywhere else in this document. An Audit Identity under is entitled to every one of them, unredacted, over reconciliations addressing the register whose agreement declares it; the Entitlement clauses below state the other parties and do not repeat that. The Ledger Head Statement of is not a read of the Ledger: it is a published statement about the Ledger, served without authentication at a well-known URI, and is deliberately outside this section so that a party holding no entitlement at all can still observe a head.

• GET /arp/outputs/{reconciliation-hash} returns the sealed Reconciliation Output. Entitlement: an Audience Member of that Output; an Audit Identity under for a reconciliation addressing its register; and a regulator in scope for that reconciliation under , whose response is field-restricted by that section.
• GET /arp/reconciliations/{reconciliation-identifier}/registers/{register-identifier} returns the Per-Register Result Set entry concerning that register alone, keyed on the Reconciliation Identifier the register received in its Per-Register Claim Projection, since a register never holds a Reconciliation Hash. Entitlement: the Register Operator of that register. It is what lets a register see what was recorded of its own answer. Without it a server could discard a register's signed match and record register-unresponsive, and the only party holding the contradicting artefact would have no operation with which to produce it.
• GET /arp/outputs returns, for the Outputs whose Audience Set names the authenticated principal, the Reconciliation Hash, the Reliance Horizon and the Entry Sequence Number of the reconciliation entry that records each. It is ordered by that Entry Sequence Number descending, which is a total order and needs no tie-break. A since parameter carrying an UTC time is REQUIRED; a server MUST return at most 100 entries and MUST carry a next parameter value in the response where more exist, which the requester supplies on the following request. Entitlement: any authenticated principal, as to its own membership only; and an Audit Identity, as to the Outputs of reconciliations addressing the register whose agreement declares it, without which an auditor entitled to Outputs by hash would hold no operation that yields the hashes.
• GET /arp/continuations/{reconciliation-hash} returns the Continuation entries of carrying that Reconciliation Hash, in Entry Sequence Number order, and no reconciliation entry. Entitlement: an Audience Member of the Output that Reconciliation Hash identifies, or a regulator in scope for that reconciliation under .
• GET /arp/entries/{entry-sequence-number} returns one Ledger entry. Entitlement: a regulator, subject to ; an Audience Member, for an entry carrying a Reconciliation Hash it is entitled to; and a Register Operator or regulator requesting the Self-Entry Hash alone, for the consistency check of , by the fields=self-entry-hash query parameter. Any requester whose signature verifies under is additionally entitled to the four-element array of the Entry Sequence Number, the Prior-Entry Hash, the Self-Entry Hash and the Signing Input Digest of that entry's Entry Signature, by the fields=linkage query parameter, which is what a witness reads to produce the Segments of . The projection is additionally available for a contiguous range, by the OPTIONAL through parameter naming an Entry Sequence Number at or above the one in the path, the response carrying the linkage array of every entry from the one in the path up to and including the lowest of the value in through, the head bound below, and the highest the server elects to serve. A server MUST serve at least one thousand entries in one such response where that many lie in range, which is the Segment cap of , so that a witness can produce one Segment from one read. A response that stops short carries the entries it served and the requester continues from the next Entry Sequence Number, so a range longer than a server elects to serve draws no refusal and no status a shorter one would not have drawn. A ranged read counts as one request against the limit of , save for the fixed allowance that section makes each interval for a witness principal so that a rate limit cannot void the publication obligation of . That allowance does distinguish a witness from another principal, by the number of reads admitted rather than by the answer to any one of them, and what it discloses is that the reading key is in a Witness Set some Agreement the deployment holds declares. That is a wider set than the effective Witness Set publishes, so the allowance is a disclosure and is recorded as one in . Every linkage read is only for an Entry Sequence Number at or below the head of the most recently published Ledger Head Statement, and a ranged read is bounded at that head in the same way. A linkage read naming a higher sequence number MUST be refused with 404 whether or not the entry exists. Without that bound the projection is a live head oracle: the Ledger is contiguous, so a requester could binary-search the current head between publications and poll it for the write rate, which is the disclosure publishes the head once per notarisation interval to prevent. Bounded, the projection carries no Reconciliation Hash and no structural metadata and discloses nothing beyond the chain shape below a head that is already published unauthenticated. It is rate-limited as provides.
• GET /arp/post-seal-records/{post-seal-evaluation-record-hash} returns the Post-Seal Evaluation Record of . Entitlement: as for the Continuation entry that carries the hash.
• GET /arp/sweeps/{examined-set-root}/inclusion/{claim-hash} returns an inclusion proof of that Claim Hash under that Examined-Set Root. Entitlement: a party entitled to a reconciliation carrying that Claim Hash. The Statement is keyed on its Examined-Set Root rather than on its timestamp, which is pinned to whole seconds and would collide where two triggers fall in one second.
• GET /arp/re-notifications returns the Sovereign Re-Notifications of whose Notification Timestamp falls in the interval named by REQUIRED since and until parameters, at most 100 per response under the same next rule. Entitlement: a regulator, as to notifications addressed to it.
• GET /arp/sweeps returns the Evaluation Sweep Statements of whose Evaluation Sweep Timestamp falls in the interval named by REQUIRED since and until parameters, at most 100 per response under the same next rule. Entitlement: a Register Operator, a regulator or an Audience Member. Its counts are deployment-wide aggregates and disclosing them to a party named in one Audience Set is a real cost, recorded in ; the Statement is a signature over a fixed array and cannot be served with fields removed without destroying the signature that makes it worth serving.

The enumeration is what makes the Entry Sequence Number of a party's own reconciliation entry reachable. Without it an Audience Member entitled to that entry under would have no operation that maps its Reconciliation Hash to a sequence number, and its only route to an entitlement this document grants would be the sweep of GET /arp/entries/{n} that the rate limit below exists to prevent.

Responses Every response to an operation of or to the commissioning request of , including every 4xx other than the 401 of , MUST be a COSE_Sign1 by the reconciliation-server sealing key, under the media type registered in , whose payload is the CBOR array ["arp-read-v1", request-binding, status, response-time, as-of-sequence-number, as-of-self-entry-hash, result] where:

• request-binding is the SHA-256 digest over the CBOR array of the request's @method, its @target-uri normalised as in Section 6.2.2 and 6.2.3 of , the request's nonce, and its keyid. Digesting a normalised binding rather than echoing the target as sent leaves nothing to disagree about and binds the response to one requester and one request.
• status is the HTTP status code.
• response-time is the time the response was produced, in the timestamp form of .
• as-of-sequence-number and as-of-self-entry-hash MUST be those of the Ledger head at the moment the read was served, and MUST NOT be those of any earlier entry. A response naming a head lower than the most recently published Ledger Head Statement is non-conforming, and a reader MUST reject one: a server free to answer against a head it chooses could suppress a supersession indefinitely by answering truthfully about a stale head, and its answer would never contradict anything.
• result is the operation's result, an empty array where the operation is set-valued and nothing matched. On a 404 it is an empty array. On the 422 or 403 of it is the Remediation Advisory, which is the artefact a refused requester needs; on a 429 it is an empty array.
• For a response to the commissioning request, as-of-sequence-number and as-of-self-entry-hash are those of the Ledger head at the moment the response was produced, and the request-binding digest is taken over a five-element array, the request's content-digest appended after its keyid.

Signing errors as well as successes is the load-bearing part. A server that signed only its successes could suppress any continuation channel by answering 404 or 429 forever, and the party it was suppressing would hold an unsigned status line: no proof that it asked, no proof of what it was told, and no way to distinguish suppression from a hash that names nothing. Binding the response to the requester's nonce and key, and stamping it with a time, is what stops a server serving one party's response to another or replaying a year-old empty result; without those the same bytes verify forever and against everybody. A reader MUST check that the request-binding matches the request it sent, that the as-of-sequence-number is at least that of the most recent Ledger Head Statement it has seen, and that the response-time is fresh. The response-time is fresh where it is no earlier than the instant the reader received the response less the declared tolerance, and no later than 60 seconds after that instant. A reader MUST reject a response whose response-time falls outside that interval in either direction. The reference instant is the reader's receipt of the response and the direction is backward, stated here for the reason gives for stating them there: a tolerance with no reference instant and no direction is a test two implementations apply differently to the same response. The forward bound is stated because response-time is produced on the responding service's clock and tested against the reader's, and nothing in this document synchronises the two. Without it, a response stamped ahead of the reader's clock and a response produced at the instant it claims are one value to the check, and a server whose clock runs fast is indistinguishable from one stamping ahead deliberately. The sixty seconds is the figure this document already uses wherever one party is bounded against another's clock: the reconciliation server against the register's, in the Freshness Timestamp of , and the server against the requester's, in the created parameter of . Both of those run toward the server. This is the return direction, and it is the one the document had not stated. Neither party is required to hold a reference clock: the rule bounds the disagreement rather than removing it, which is what a two-clock test can do. A deployment MUST declare that tolerance in its Bilateral Register Agreements, it MUST be at least sixty seconds, and it MUST NOT exceed the effective ledger-head notarisation interval of or sixty seconds, whichever is longer, that interval being the shortest any Bilateral Register Agreement the deployment holds declares, per the direction rule of : a tolerance left to each reader is not a property two implementations can be tested against; one shorter than the transit and clock disagreement between the two parties rejects every honest response, the backward bound running from the reader's receipt and the response having been produced before it; and one longer than the notarisation interval would admit a response naming a head the reader could already know to be superseded. Without those checks a server may serve a cached response for a repeated request tuple indefinitely, and the properties below do not hold. An empty result is therefore an assertion and not an absence: a signed statement that as of a named head, at a named time, in answer to this requester's request, there was nothing. A continuation-supersession entry later found at or below that head contradicts it, in one operator's own signature. That contradiction is conditional on the reader and the later observer having been served one chain, and the condition is load-bearing. states that detection of a fork is opportunistic: an operator publishing to two audiences at disjoint sequence numbers never emits a colliding pair. Under such a fork the superseding entry lands on a branch the holder of the empty result never reads, the at-or-below test never fires, and the assertion stands uncontradicted for as long as the branches are kept apart. An empty result is therefore an assertion about a named head on the chain its reader was served, and it is falsifiable to the extent that the reader holds head-consistency evidence for that chain from an observer independent of the responding service. Head evidence obtained only from that service does not bound this. A fork at disjoint sequence numbers is invisible from a single vantage by construction, and the vantage is what is in question: equivocation is precisely the condition that no single consistent chain explains two observations, so it becomes observable when two independent observers compare heads and not before. A relying party acting on an empty result SHOULD hold head-consistency evidence for the served chain from at least one observer independent of the responding service -- a witness countersignature over the head, or, where no Witness Set is available, an independently anchored head digest, in decreasing order of strength. specifies the Witness Set and the Witness Quorum, so that "at least one observer independent of the responding service" is a condition a deployment declares a value for and an implementation can be tested against, rather than a property each reader decides for itself. What that quorum does and does not establish is stated in : it is independence declared, not independence proven, and this document still does not claim to close the gap. The contradiction is only as tight as the operator's freedom to defer. A continuation-supersession entry MUST be appended within the ledger-head notarisation interval of , measured from the completion of the Evaluation Sweep that produced the superseding Output -- an event the Evaluation Sweep Statement of dates and signs, and which therefore exists for an immaterial supersession as much as for a material one. Where the supersession is the revocation of a Verified Principal Credential and no superseding Output is produced, the deadline runs from the completion of the sweep the revocation triggered, which likewise dates and signs. Measuring from "the material change" would leave both that case and an immaterial supersession with no start point and so no deadline. Without a deadline an operator defers every supersession above the highest head it has ever named and no contradiction ever arises.

Error semantics A request that is well-formed and signed but that names a resource the requester is not entitled to, and a request naming a resource that does not exist, MUST both be refused with 404. Only an entitled requester receives 200. Answering 403 for the first and 404 for the second would turn every endpoint into an existence oracle: a party could sweep Reconciliation Hashes, or sequence numbers, and learn what a deployment had done without being entitled to any of it. The two cases MUST be equivalent under the normalised observation this section defines, rather than byte-identical, which a conforming server cannot make them: requires every response to bind the request and the serving instant, so the request-binding, the response-time, the As-Of pair and the resulting signature differ between any two requests whether or not the resource exists. A requirement of byte equality would be unsatisfiable, and a test written against it would fail every conforming implementation. The normalised observation of a response is that response with exactly those four values removed. Two responses are equivalent when their normalised observations are equal. Across the two cases a server MUST therefore produce the same status, the same media type, the same set of HTTP header field names, the same set of protected COSE header parameters, the same empty-result representation, the same cache directives and the same rate-limit effects, and the signed payload MUST NOT carry any error discriminator whose value depends on whether the resource exists. Every value removed by normalisation MUST still be valid for its own request: normalisation is how two responses are compared, not a licence to omit a required field or to carry an existence-dependent discriminator inside one. A response to either case MUST carry Cache-Control: no-store. A response bound to a nonce and a serving instant is not reusable by another requester, and a cache that retained one case and not the other would reintroduce through intermediaries the distinction the rest of this section removes. Two channels survive that rule and MUST be closed with it. A server MUST charge the rate-limit counter before evaluating entitlement, so that an unentitled request and a nonexistent one consume the same budget and a burst of each yields the same sequence of statuses. And entitlement evaluation MUST NOT be short-circuited: a server MUST perform the same work for a Reconciliation Hash it does not hold as for one whose Audience Set does not name the requester, so that the two do not differ in response time. Response timing is a separate claim from the requirements above and MUST be stated separately. Serving both cases from one processing path is evidence about the design and is not evidence that the two latency distributions are indistinguishable to an observer. An implementation that claims resistance to timing-based existence inference MUST publish the measurement population, the sample count, the network placement of the measurement, the decision rule and the acceptance threshold under which the two response classes were compared. An implementation that makes no such claim is not for that reason non-conforming: the requirements above are met or not met independently of it, and conflating the two would let a deterministic conformance failure be excused as a measurement artefact, or a measurement result be read as protocol conformance. The fields=linkage projection of answers 200 for an entry whose full read the same requester would be refused, and is not an existence oracle for two reasons that both have to hold. The Ledger carries a contiguous Entry Sequence Number and publishes the head unauthenticated, so existence at or below that head is already public and the projection discloses no fact about which entries exist. And the projection is bounded at that published head, so it cannot answer the one existence question that is not already public, which is where the head is now. A projection that widened either -- serving a non-contiguous ledger, or serving above the published head -- would be an oracle, and neither is permitted. A server MUST rate-limit these operations, per authenticated principal, at the most permissive rate any of its Bilateral Register Agreements declares, and MUST answer 429 when the limit is reached. The declared rate MUST admit at least one read of each operation per Reconciliation Hash per reliance interval, so that a limit cannot silently void the obligation of . A server MUST NOT count against that limit the first sixty ranged linkage reads made in each effective ledger-head notarisation interval, being the shortest item 15 any Bilateral Register Agreement the deployment holds declares, by a principal whose keyid resolves to the key of a Witness Entry any Bilateral Register Agreement the deployment holds declares, so that a limit cannot silently void the publication obligation places on a witness. The allowance is a fixed count outside the declared rate rather than a second rate inside it: item 18 of carries one request count and one interval, and a per-class rate would be a negotiated term sitting outside the Agreement Hash. Sixty reads of the thousand entries obliges a server to serve in one of them cover sixty thousand appends in an interval; a deployment appending faster declares a shorter interval or a higher rate, which are its own terms and not a third party's cadence. GET /arp/entries/{n} in particular ranges over the whole Ledger; unlimited, a party entitled to one consistency check could sweep for the deployment's entry count, write rate, and the timing of retroactive bursts, which is disclosure by aggregation of a surface every individual answer to which is innocuous. A read served under with any field redacted MUST NOT return the Prior-Entry Hash or the Self-Entry Hash of that entry, and MUST NOT return the Prior-Entry Hash of the entry that follows it, which is the Signing Input Digest of the redacted entry's Entry Signature and so covers every field of that entry including the fields being withheld. The Self-Entry Hash is a digest over the entry's own fields and carries no blinding value; a reader holding the leading fields and denied the type-specific block could otherwise recover the block by search over register subsets, a small aggregation descriptor set, four binding classes and a bounded timestamp, and would do so off the audit trail that section imposes. A redacted field is returned as CBOR null in its position, so that the array's length is still the length fixed by the Entry Type; a regulator receiving a redacted entry therefore cannot verify its chain hashes, which is the price of redaction and is why an unredacted read is the ordinary case. Each read served under this section MUST be recorded in an append-only access log, retained for the period of , sequenced, chained, headed and notarised as the audit trail of is and for the same reason. The log is not the Settlement-Layer Ledger and MUST NOT be written to it: who asked a question is not a fact about the reconciliation, and a Ledger that recorded reads would disclose the pattern of interest in a subject to every party entitled to read it. The log is readable only by a regulator under and by an Audit Identity under , to which it is disclosed out of band as the policy-epoch material is; the reasoning that keeps it off the Ledger applies equally to the log itself.

SCITT Reference API Binding A Reconciliation Output MAY be notarised into a SCITT Transparency Service as a transparent statement. Where it is, an implementation MUST use the binding in this section. states the architectural relationship; this section states the wire behaviour, so that two implementations registering the same Reconciliation Output against the same Transparency Service produce interchangeable results.

Registration The Reconciliation Output MUST be registered as a Signed Statement by POST /entries as defined in , with the HTTP Content-Type that document requires on that request. A Transparency Service returns a Location header on both 201 Created and 202 Accepted; an implementation MUST use it in both cases rather than constructing a polling URL of its own. Notarising an Output does not enlarge its Audience Set. Registration places the sealed Output in a log whose retrieval is by EntryID, and a party that obtains it that way holds it on the terms of : it may verify the Sealing Signature and read the Combined Verdict, and it obtains no read under and no notice of supersession. A deployment for which that is the wrong disclosure should not notarise; is composed permissively for that reason. The payload of the Signed Statement MUST be the sealed COSE_Sign1 -- the Reconciliation Output under its Sealing Signature, as produced by -- and MUST NOT be the bare Reconciliation Output. Nesting is what makes the requirements below checkable: a relying party holding only the bare Output has neither the sealing key identity nor the Policy-Version Hash the seal committed to, and could not verify either. The Signed Statement is therefore a COSE_Sign1 whose payload is itself a COSE_Sign1. Its protected header MUST carry:

• the content type application/arp-sealed-reconciliation-output+cose, registered per . The outer payload is a COSE_Sign1 wrapping a Reconciliation Output, not a Reconciliation Output, and labelling it with the latter's media type would have a conforming decoder parse a signature envelope as an Output;
• arp-policy-version-hash;
• arp-bilateral-agreement-hash, carrying the array of the Bilateral-Register-Agreement Hashes of the addressed registers, sorted in lexicographic byte order as required by . A Reconciliation Output aggregates registers under more than one agreement, and an unordered encoding would make two conforming implementations produce non-interchangeable Signed Statements.

The outer COSE_Sign1 MUST carry a kid in its protected header, MUST be signed under a key resolvable through , and that key's Sealing-Key Identifier MUST equal the Sealing-Key Identifier of the nested Output in both components. A relying party MUST verify the outer signature and that equality. "Signed by the server that sealed it" is otherwise not a predicate a relying party can evaluate: any operator of a conforming server could wrap another server's sealed Output, sign it under its own resolvable key, and every other check here would pass, and the Receipt would attribute the statement to the Transparency Service and to nobody else. Fixing the nested payload closes a false-policy-version attack; fixing the outer signer closes a wrong-registrant one. The arp-bilateral-agreement-hash in the outer protected header MUST equal the value carried in the nested sealed COSE_Sign1, and the arp-policy-version-hash in the outer protected header MUST equal the Policy-Version Hash carried in the nested sealed COSE_Sign1. A relying party MUST verify the Sealing Signature over the nested payload, MUST verify that equality, and MUST reject the Signed Statement where either fails. The verification key for the Sealing Signature is identified by the Sealing-Key Identifier of , whose kid component MUST equal the kid in the protected header of the nested COSE_Sign1, and is resolved through . A relying party that cannot resolve the Sealing-Key Identifier MUST NOT rely on the notarised statement. Without nesting and this equality the Signed Statement would be a second and independent envelope: any party holding a valid Reconciliation Output could register it under a protected header asserting a policy version it was not sealed under, and a relying party following would believe that assertion. A protected header cannot be altered after signing, but it can be false when signed, and integrity is not correctness. The payload MUST NOT be the Verifiable Credentials serialisation of . That form is an interop convenience for relying parties and is not the notarised object; registering it instead would notarise a representation whose canonical form is unspecified.

Asynchronous registration A Transparency Service may register synchronously or asynchronously, and an implementation MUST support both. This is the most likely source of divergence between two otherwise conforming implementations, and is therefore stated as a requirement rather than left to the referenced document. On 201 Created the Receipt is available immediately. On 202 Accepted the response carries a Location header, and the implementation MUST poll that URL verbatim rather than constructing a path of its own. A 204 No Content means registration is still in progress and MUST NOT be treated as failure or as a negative result. A 4xx other than 404 returned synchronously by POST /entries is a terminal refusal and MUST NOT be retried under the same Signed Statement; it is the ordinary refusal case and is recorded as such under . A 404 Not Found ends polling and MUST NOT be polled further. It carries two meanings in -- that no Receipt was found for the specified EntryID, and that an asynchronous registration has failed and no Receipt will be produced -- and an implementation MUST distinguish them from the response body where the service supplies one, because the second is a registration failure and the first may follow from having polled a URL the Transparency Service did not issue. Ending polling is not the same as resolving the outcome: only the second meaning is a terminal refusal for the purposes of , and a 404 the implementation cannot resolve to one meaning or the other is recorded as an incomplete notarisation, not as a refusal. An implementation MUST honour a Retry-After header where one is present, MUST NOT poll more frequently than once per second in its absence, and MUST bound total polling, to the shortest bound any Bilateral Register Agreement addressed by the reconciliation declares; a bound of 300 seconds is RECOMMENDED where the Bilateral Register Agreement declares none. Exhaustion of the bound MUST be recorded in a Post-Seal Evaluation Record carrying notarisation-incomplete per , rather than as either success or refusal. A Reconciliation Output whose notarisation is incomplete remains valid under its Sealing Signature; notarisation is an additional property, not a precondition of validity.

Sealing-key discovery A signed key set, wherever this document requires one, is a COSE_Sign1 whose payload is the deterministically encoded CBOR serialisation of the COSE_KeySet, under the media type registered in . Each key in the set carries the arp-key-status and arp-key-validity COSE Key common parameters registered in . An Authorised-Origin Document is a COSE_Sign1 whose payload is a CBOR array of three-element arrays -- the server's authority origin, the identifier of the key signing its sealing key set, and the identifier of the key signing its operator key set -- sorted in bytewise lexicographic order of the origin. A relying party is not a party to any Bilateral Register Agreement and holds only the hashes of those agreements. It therefore cannot resolve the sealing key from them, and a binding that assumed otherwise would oblige every conforming relying party to refuse every Reconciliation Output. A reconciliation server MUST publish its sealing keys as a COSE Key Set at /.well-known/arp-sealing-keys on the reconciliation server's authority origin, and a single key by identifier at /.well-known/arp-sealing-keys/{kid_value}. The Sealing-Key Identifier is the pair of that origin and the kid. A key identifier in this document is in every case the JWK thumbprint of , base64url-encoded without padding. It is carried as a CBOR text string in every payload field and in every keyid signature parameter, as the UTF-8 encoding of that same text string in a COSE kid (label 4), which makes a byte string, and as that text string unaltered in a {kid_value} path segment. Every equality test this document requires between a kid and a Sealing-Key Identifier component is over the base64url text. Without one pinned form the same key has three spellings and those equality tests compare values of different CBOR types. With that fixed, it is the kid component that is compared. Resolving a key is not sufficient. Web PKI establishes that an origin is the origin it claims to be; it does not establish that the origin is entitled to seal Reconciliation Outputs naming a given register set. A relying party that accepted any well-formed key set would accept an Output minted by any party able to stand up a host, since the Bilateral-Register-Agreement Hashes can be copied from a genuine Output and are one-way. Each Bilateral Register Agreement MUST therefore declare the Authority Origin of the reconciliation server it authorises, and each register operator MUST publish an Authorised-Origin Document at /.well-known/arp-authorised-origins on its own register origin. A Register Identifier is an origin, so the register origin is a member of the Addressed-Registers Identifier Set and is known to the relying party from the Output. An Authorised-Origin Document is a COSE_Sign1 whose payload comprises, for each reconciliation server the register operator has authorised, that server's three-element array of : its authority origin, the identifier of the key signing its sealing key set, and the identifier of the key signing its operator key set. It MUST be signed under a key served in a COSE Key Set at /.well-known/arp-register-keys on the same register origin -- a key set carrying the same arp-key-status and arp-key-validity parameters as a sealing key set, so that a compromised register key has an in-band revocation path, and the same key set that resolves a register's signatures on Partial Attestations and Non-Answer Statements -- which the relying party fetches over its ordinary web PKI. Signing it matters for the same reason signing the sealing key set matters: an unsigned document fetched over TLS can be varied per audience, and this one is the root of the chain. A relying party MUST verify that the origin component of the Sealing-Key Identifier appears in the Authorised-Origin Document published by every register in the Addressed-Registers Identifier Set, and MUST reject the Output where it does not or where any such document cannot be verified. The chain is then: register origins from the Output; each register's own key from its register origin; the Authorised-Origin Document verified under that key; the authorised server origin and its key-set signing key identifier from that document; and the sealing key from the server's key set, verified under that identifier. Every step is fetchable by a party holding only the Output. A key entry MUST carry the arp-key-validity and arp-key-status parameters of active, retired or revoked, and an entry whose status is revoked MUST carry a revocation time as the third element of arp-key-validity. A relying party MUST reject a Sealing Signature made under a revoked key whose Reconciliation Timestamp falls at or after the revocation time that key entry carries, MUST reject a Sealing Signature made under a revoked key carrying no revocation time irrespective of when the Output claims to have been sealed, MUST accept one made under a retired key only where the Reconciliation Timestamp falls within that key's validity interval, and MUST reject one whose Reconciliation Timestamp falls outside the interval of the key it resolves to. A key MUST NOT be removed from the set while any Reconciliation Output it sealed may still be relied upon: retirement is by status, not by deletion, so that a historical Output remains verifiable while a compromised key can still be refused. Revocation without a time is repudiation of an epoch. Earlier revisions scoped retired by validity interval and left revoked unscoped, so one status change in a document the reconciliation server publishes, on its own origin, under its own key, invalidated every Reconciliation Output, Evaluation Sweep Statement, signed read response and Entry Signature that key had ever made. The rule closing removal -- a key MUST NOT be deleted while an Output it sealed may be relied upon -- was defeated by status, which is the same act with a different verb. The reconciliation server MUST therefore publish and notarise its sealing key set as requires of the Policy Parameters Document: with a Publication Timestamp, notarised into the Transparency Service of on the ledger-head notarisation interval, and republished on that interval whether or not its contents changed. A relying party MUST NOT act on a status transition it cannot date. A COSE_Sign1 is not dateable from its own bytes, and a status flip that no party can place in time disarms every party it disarms without any of them being able to say when, or to show that it happened after the Output they hold. The key set MUST itself be signed under the key whose identifier the Authorised-Origin Document gives for that server, and a relying party MUST verify that signature. The identifier comes from a document the relying party can fetch, not from an agreement it does not hold. A key set fetched over TLS alone can be varied per audience, which would let a server present one key to one relying party and another to a second and seal two contradictory Outputs for the same reconciliation, each verifiable only by its intended audience -- reopening at the origin the equivocation that closes at the Transparency Service.

Receipt validation A relying party MUST validate the Receipt against Transparency Service keys obtained from GET /.well-known/scitt-keys, or from GET /.well-known/scitt-keys/{kid_value} for a single key identified in the Receipt.

Policy-version determination A relying party MUST determine the Policy Version of a notarised Reconciliation Output from the arp-policy-version-hash parameter in the verified protected header of the Signed Statement, and MUST NOT determine it from any retrieval path, query parameter or Transparency Service index entry. Because the parameter is in the protected header, it is covered by the Receipt; and because requires the sealed COSE_Sign1 to be the nested payload and the outer parameter to equal the Policy-Version Hash it carries, what the header asserts is verifiably what the seal committed to. The policy version is therefore established by verification rather than by lookup, and a Transparency Service that indexed an entry incorrectly, or presented different index results to different relying parties, cannot cause a relying party to attribute a Reconciliation Output to a policy version it was not sealed under. This holds only because of the nesting and equality requirements in , both of which the relying party checks. A protected header alone establishes that a value was not altered after signing, not that it was true when signed. defines retrieval by EntryID and defines no query surface. Correlating entries by policy version is consequently outside the scope of this binding and is a property of the deployment, not of the protocol. An implementation MUST NOT assume a standard retrieval path keyed on the Policy-Version Hash exists.

Verifiable Credentials Interop A Reconciliation Output MAY be additionally serialised as a Verifiable Credential conforming to and secured as application/vc+cose under . The COSE_Sign1 of is the normative form. The credential is a projection of it for relying parties that operate in W3C VC ecosystems, and it states what the Output establishes about a claim in the vocabulary those ecosystems evaluate. This section is the complete profile; a conforming credential satisfies every requirement below, and a verifier applies every verification step below.

Credential Form The credential is a JSON object with these members.

Member	Value
@context	the array of exactly two elements: https://www.w3.org/ns/credentials/v2, then an object whose only member is @vocab, set to https://datatracker.ietf.org/doc/draft-hillier-scitt-arp/vocab#
type	the array VerifiableCredential, ArpReconciliationOutput and no other element
id	urn:arp:reconciliation: followed by the Reconciliation Hash
issuer	the Authority Origin of the Sealing-Key Identifier, as a text string
validFrom	the Reconciliation Timestamp
validUntil	the Reliance Horizon
credentialSubject	an object with the members below

Every byte string rendered into the credential is rendered as base64url without padding (Section 5 of ), the single rendering requires. Every timestamp is in the form YYYY-MM-DDTHH:MM:SSZ fixed by .

Subject member	Value
reconciliationHash, claimHash, policyVersionHash	the 32-octet values of the same names
combinedVerdict	the Combined Verdict, one of match, no-match, partial-match, indeterminate
requesterBindingClass	the Requester-Binding Class
addressedRegisters	the Addressed-Registers Identifier Set, in the order of
bilateralRegisterAgreementHashes	the Bilateral-Register-Agreement Hash Set, in the order of
reconciliationTimestamp, relianceHorizon	the Reconciliation Timestamp and the Reliance Horizon
audienceSet	an array with one object per Audience Member, in the order of , carrying id (the Audience Member Identifier) and verificationMethod (the Verification Method Reference)
sealedOutput	an object carrying digestAlgorithm (sha-256), digest (the SHA-256 digest of the serialised COSE_Sign1 of the sealed Reconciliation Output) and mediaType (application/arp-sealed-reconciliation-output+cose)

The credential carries no Subject Identifier, no Attested Value, no Per-Register Result Set and no register record. The members above are the whole of it. A credential with a member outside them, at the top level or in credentialSubject, is refused: an added member is the route by which register content or a redefined term enters a signed document, and the second element of @context is fixed for the same reason, because a context that redefines combinedVerdict changes what a JSON-LD processor reads under a valid signature. validUntil is the Reliance Horizon and validFrom is the Reconciliation Timestamp. A W3C verifier that treats validUntil as expiry therefore stops treating the Combined Verdict as current at the instant requires, with no ARP-specific code. The Horizon bounds reliance and does not invalidate the Output, and the credential carries the same meaning: after validUntil the Sealing Signature still verifies and the verdict remains true of the moment it was sealed.

Securing The credential is secured as a COSE_Sign1 under Section 3.3.1 of .

• The payload is the credential serialised under and encoded as UTF-8. A verifier compares the payload to the serialisation of its own parse of it, because a signature over a second serialisation of one credential is a second signing act over one statement.
• The protected header carries alg (1, the value -8, EdDSA), kid (4), typ (16) and the content type (3). A verifier reads all four from the protected header only; a value in the unprotected header is not evidence of anything. typ is application/vc+cose. The content type is application/arp-reconciliation-output+json, the more specific type that Section 3.3.1 of permits in place of application/vc. The kid is the UTF-8 encoding of the JWK thumbprint of the Sealing key, as states for every kid in this document.
• The signing key is the Sealing key. The pair of issuer and kid is the Sealing-Key Identifier of the Output the credential projects, and it resolves through .
• The iat and exp CWT claims, where present in a COSE header, describe the signature. A verifier MUST NOT read either as the Reconciliation Timestamp or the Reliance Horizon. In the SD-JWT VC form exp is a payload claim and carries validUntil.

Verification A relying party that receives the credential MUST perform every step. A failure at any step is a refusal to rely, and the step that failed is the reason recorded.

1. Resolve the key for the Sealing-Key Identifier formed from issuer and kid through and verify the COSE_Sign1 under it.
2. Check typ, the content type and alg against .
3. Check that the payload is the serialisation of its own parse. A payload with a duplicated member name, a string spelled with an escape that does not produce, or members in any other order fails here.
4. Check that @context and type are exactly the values of , that issuer equals the Authority Origin of the key resolved in step 1, that every member of is present, that no other member is, and that id is urn:arp:reconciliation: followed by reconciliationHash.
5. Check that validFrom equals reconciliationTimestamp, that validUntil equals relianceHorizon, that validFrom is earlier than validUntil, and that every timestamp has the required form.
6. Check that audienceSet is present and non-empty, and that its members are distinct and in the order of . An Audience Set is never empty (), and a credential without one is the bearer artefact exists to retire.
7. Check that combinedVerdict is one of the four defined values, and that every byte string is rendered in the single form of : unpadded base64url that decodes to the length the field has and re-encodes to the same text. The Bilateral-Register-Agreement Hash Set is sorted and deduplicated.
8. Where the sealed Reconciliation Output is held, check that sealedOutput.digest equals its SHA-256 digest and that reconciliationHash equals the Reconciliation Hash recomputed from it. Where it is not held, the verdict is a snapshot of unknown provenance until the Ledger entry for reconciliationHash has been read under .
9. Compare the evaluation time to validUntil. After it, the Combined Verdict MUST NOT be treated as current under .

Steps 1 to 8 determine whether the credential is genuine. Step 9 determines whether it is current. A genuine credential evaluated after its Horizon yields a stale outcome, which differs from a refusal: the verdict is authentic and its reliance window has closed. A relying party that is not an Audience Member holds a credential that carries the Audience Set it is not on. applies to it exactly as it applies to the COSE_Sign1 form.

JOSE Securing Forms The credential of has three further securing forms. All four carry the same credential, verify under the same Sealing key, and resolve that key through . A relying party applies the verification steps of to the credential it recovers from any form. vc+jwt. The credential is secured as a compact JWS under Section 3.1.1 of . The payload is the serialisation of the credential. The protected header carries alg EdDSA, kid (the JWK thumbprint of the Sealing key, ), typ vc+jwt and cty vc, and no other member. The media type is application/vc+jwt. SD-JWT VC. The credential is secured as an SD-JWT VC under and . The protected header carries alg EdDSA, kid and typ dc+sd-jwt. The payload carries iss (the credential's issuer), jti (its id), iat and nbf (validFrom), exp (validUntil), vct (https://datatracker.ietf.org/doc/draft-hillier-scitt-arp/vct#reconciliation-output), _sd_alg sha-256 and _sd, a sorted array of digests. Four credential subject members are always in the clear: reconciliationHash, combinedVerdict, reconciliationTimestamp and relianceHorizon. Seven are selectively disclosable, each with its own Disclosure: claimHash, policyVersionHash, requesterBindingClass, addressedRegisters, bilateralRegisterAgreementHashes, audienceSet and sealedOutput. The issuer serialisation carries every Disclosure and no key-binding JWT. A holder presents a subset of the Disclosures. The media type is application/dc+sd-jwt. A verifier of the SD-JWT VC form MUST refuse a Disclosure whose digest is not in _sd, a Disclosure presented twice, a Disclosure that names a member that is in the clear or is not one of the seven, and an _sd that is not sorted. The members recovered from the Disclosures and the clear members together are the credential subject of , and steps 4 to 7 of apply to the credential as the issuer serialised it, with every Disclosure present. The clear members map to that credential as iss to issuer, jti to id, nbf to validFrom, exp to validUntil and vct to the credential type, the subject members are top-level claims, and the credential's @context is the constant fixes. A presentation that omits a Disclosure states less than the credential does and states nothing different: a verifier applies the Disclosure rules above, the clear members and the key binding to what it received, and treats each member it did not receive as not stated. Where the issuer binds the credential to a wallet key, cnf carries that key as a jwk, and a presentation of that credential carries a key-binding JWT after the final tilde, per . The key-binding JWT has alg EdDSA and typ kb+jwt; its payload carries iat, aud, nonce and sd_hash, the base64url SHA-256 of the presentation up to and including its final tilde. A verifier MUST refuse a presentation of a bound credential that carries no key-binding JWT, one whose signature does not verify under cnf.jwk, and one whose aud, nonce, freshness or sd_hash does not match what the verifier issued and received. The Audience Set of is carried in every form and is not made optional by selective disclosure: a holder that withholds the audienceSet Disclosure presents a credential the relying party cannot place itself on, and applies to that presentation. mdoc. The credential is secured as an IssuerSigned structure of , profiled so that the issuer key resolves by thumbprint through where carries an X.509 chain. Each credential subject member is one data element in the namespace and docType com.certisyn.arp.reconciliation.1, carried as an IssuerSignedItemBytes (tag 24) of digestID, random, elementIdentifier and elementValue. The issuerAuth is a COSE_Sign1 () whose protected header carries alg -8 and kid (the thumbprint of the Sealing key) and whose payload is a Mobile Security Object (tag 24) holding version 1.0, digestAlgorithm SHA-256, the SHA-256 digest of every IssuerSignedItemBytes under valueDigests, the holder's deviceKey as a COSE_Key under deviceKeyInfo, the docType, and validityInfo (signed, validFrom, validUntil) equal to the credential's window. Encoding is the core deterministic encoding of . A verifier MUST refuse an issuerAuth that does not verify under the Sealing key, an item whose digest is not in valueDigests, a digest with no item, a repeated digestID, a docType other than the one it requested, a validity window that excludes the evaluation time, and a deviceKey other than the holder key the relying party expects. The elements recovered from the items are the credential subject of . Issuer metadata. The issuer publishes the metadata document of : issuer (the credential's issuer) and jwks, a JWK Set that holds the Sealing key with kid equal to its thumbprint. A relying party resolves the Sealing key from this document or through and pins it before it accepts a credential in any form.

Conformance Class A conformance class for this profile is published with the draft's conformance material: 30 vectors, each declaring the outcome it must produce and the one check designed to produce it, decided by two independent COSE_Sign1 and implementations that must agree on every row. Thirteen of the vectors are signed by the genuine Sealing key and fail only on profile content: a redefined context term, an added subject or top-level member, an id naming another reconciliation, a validFrom after validUntil, a padded or standard-alphabet byte string, unsorted agreement hashes, a duplicated Audience Member, a duplicated JSON member name, an escape-spelled string, header parameters carried unprotected, and an additional credential type. One vector is a genuine credential evaluated after its Horizon, whose outcome is stale. For each check a mutant verifier with that check removed must admit at least one vector the full verifier refuses. The JOSE securing forms are checked against the platform's own emission by a third implementation, hand-written over , and Ed25519, that applies 30 rows: the four forms must state one credential and one holder key, a holder presentation with its key-binding JWT must verify, and mutants of each form that the genuine Sealing key signed, or that a holder or intermediary altered, must be refused at their designed check.

Representation Invariance Every interoperability defect this document has repaired in its digest constructions is one defect. A signature that has two byte encodings for one signing act. A CBOR item whose major type the text did not fix. A set with no ordering rule, or a CBOR map whose key order two libraries decide differently. An optional member that could be omitted or nulled. A URI that could be normalised on receipt or before sending. A Unicode string in NFC or in NFD. A binary value rendered into JSON as base64, base64url or hex. A digest taken over transmitted bytes or over a re-encoding. In each case two byte strings carry the same information and a digest over them differs. The information content is invariant and the representation is not, and the digest was defined over the representation. This section states the general rule those repairs are instances of, so that the next instance is caught by the rule rather than by the next reviewer. The rule. For every digest, signature payload and comparison this document defines, the value MUST depend only on the information its input carries and MUST NOT depend on any choice of representation that carries no information. A construction that fails this is not merely inconvenient: two conforming implementations given the same facts compute different values, and every mechanism built on the value inherits the divergence. The obligation that makes it testable. A specification cannot discharge this by asserting it. For every digest it defines, this document names the representation class of each input: the set of byte strings that carry the same information as that input. The classes this document recognises are:

• Signature encoding. For ECDSA, (r, s) and (r, n - s). The class has more than two members over the wire, since a low-S rule removes one member of an unbounded set. Handled by .
• CBOR type choice. A value expressible as more than one major type: an identifier as tstr or bstr, a count as uint or text, a URI as tstr or tag 32, a timestamp as tstr or tag 0. Handled by the type tables of , , and .
• Collection order. The permutations of a set, and the orderings of the pairs of a CBOR map. Handled by the bytewise sort rules stated at each set, and for a map by the requirement of that Section 4.2.1 of be produced and that a library option named canonical not be assumed to produce it. The map case is the one place in this class where the freedom is exercised by a library default rather than by an implementer's choice, which is why it is named there as well as here.
• Absence. An optional member omitted, or present and null. Handled by the null-substitution rules, which also fix array length.
• Text normalisation. The Unicode normalisation forms of one string. Handled by the NFC requirement of .
• Reference normalisation. The equivalent forms of one URI or origin. Handled by for an Authority Origin and by normalisation for the identifiers that carry it.
• Binary rendering in a text encoding. Base64, base64url with or without padding, and hexadecimal renderings of one byte string. Handled by the key-identifier rule of and by the digest rendering of .
• Framing. A concatenation against an array, and an array against a map. Handled by the domain-separated array requirement stated at each preimage.

A specification that defines a new digest MUST state, for every element of its preimage, which of these classes the element belongs to and which member of the class the preimage takes. A registration under that introduces a value carried into any digest this document defines MUST do the same, and the designated expert MUST refuse one that does not. The conformance obligation. A conformance runner for any construction in this document MUST exercise the construction against the representation class of each of its inputs, and not against an enumeration of previously observed defects. The distinction is the whole of the test's value. A runner that checks a digest against the two ECDSA signature encodings it has heard of confirms what its author already knew; a runner that enumerates the class and asserts the digest is constant across it detects the member nobody had thought of. The same holds for every class above. Where a class is unbounded, the runner MUST sample it and MUST record in its run transcript that it sampled rather than enumerated, so that a reader is not told a property was established over a class when it was established over a sample of one. What this does not establish. Invariance across a representation class is not correctness. A digest can be perfectly invariant and taken over the wrong elements, and this rule says nothing about that. It says only that two parties holding the same facts reach the same value, which is the precondition for every other property this document claims and is not itself any of them.

Security Considerations

Service-Operator Containment The reconciliation server operates under a service-operator entity standing in bilateral contractual relationship with each Register Operator. The service-operator entity MUST NOT be given access to any register record or any Partial-Attestation payload beyond the verdict and divergence-axis fields, and a deployment MUST enforce that by construction -- by encryption addressed to the requester or by an equivalent measure that no internal operator action can reverse -- rather than by policy. A conformance test for this requirement is whether an operator holding every credential the deployment issues can obtain a register record; if it can, the deployment does not conform. Encryption addressed to the requester discharges this requirement for a register record, and for any enumerated field the reconciliation server does not read. It cannot discharge it for the Query Binding, the Freshness Timestamp, the echoed Policy-Version Hash and Bilateral-Register-Agreement Hash, the Source-Data Version Identifier Set or the Applied-Parameter Set, each of which , , and oblige the reconciliation server to read in the clear. For those fields the equivalent measure MUST be an execution boundary whose integrity is remotely attestable under and whose plaintext state no credential the deployment issues can read, and the conformance test above extends to them: an operator holding every credential the deployment issues must be unable to obtain any of them. The distinction this rests on is the one the section opens with and did not carry through. The prohibition binds the service-operator entity, a legal person, and not the reconciliation server, a process, whose reading of those six fields the sections named above require. The two named enforcement measures were therefore not alternatives of equal reach: the first is unavailable for exactly the fields where the prohibition bites, and the conformance test asked only about a register record, so the payload half of the requirement had no test at all. That property is per-event and MUST NOT be read as a property of the system under repeated querying. A verdict is a function of an attested value the requester chooses, so a sequence of reconciliations varying that value recovers the underlying record field by search, and several Divergence Axis values -- ownership-threshold-mismatch, register-record-absent, temporal-mismatch -- disclose record content on their own. Each event conforms while the sequence does not. A deployment MUST therefore declare in each Bilateral Register Agreement a query budget and the interval over which it is measured, and the budget MUST be measured per accountable principal per subject, not per subject alone. The subject half of that key is the Claim Hash of the Canonical Claim with its Predicate, Applicable-Regimes Set and Claim Timestamp elided, computed as computes a Claim Hash over the remainder. The principal half is pinned in three tiers below and the subject half was pinned nowhere, which left the counter keyed on a value the requester controls: a Subject Identifier is NFC-normalised as a string and nothing more, so case, leading zeros, jurisdiction prefixes and equivalent register-specific forms each open a fresh counter. The bound on recovery-by-search this section exists to impose was evadable by respelling, and the per-subject ceiling was a shared counter whose key a party could collide with a victim's, forcing every third-party reconciliation about that victim to indeterminate. Where the budget is shared across requesters, any one requester exhausts it for all of them -- including a requester whose Requester-Binding class is agent-unverified, which is to say a party the deployment has declined to identify -- and every subsequent reconciliation about that subject is forced to indeterminate for the remainder of the interval. That is a denial of service against every other requester, granted by the countermeasure. The recovery property this budget bounds is a property of one requester's sequence, and sequences run by colluding principals are the business of the repeated-narrowing pattern below rather than of a shared counter. The budget is keyed on the accountable principal identifier where the Requester-Binding carries one. Where it does not -- classes agent-unverified and agent-key-verified -- the budget MUST be keyed on the verified signing key where one exists, and otherwise on a deployment-declared fallback key such as the authenticated transport client identity. Every requester signs, by , so every requester has a key and none falls outside the budget. Admitting a requester to a shared counter is the denial of service this paragraph exists to remove. A deployment MAY additionally declare a per-subject ceiling across all principals. A ceiling is a shared counter and reintroduces that denial of service by construction, so where a deployment declares one it MUST partition it: a stated proportion reserved for principals of class human-operator and agent-verified, and within that proportion a per-principal sub-budget, so that no one principal can consume the reserve. Classes carrying no corroborated principal -- agent-key-verified and agent-unverified -- are charged only against the remainder. A reserve with no per-principal partition is exhausted by a subject that incorporates enough entities to hold enough corroborated principals, which is a purchase and not a barrier. A subject able to mint identities cheaply can otherwise exhaust the ceiling on itself and force every third-party reconciliation about it to indeterminate, which is a self-service veto over the verdicts this protocol exists to produce. Exhaustion of a ceiling is recorded as subject-ceiling-exhausted rather than query-budget-exhausted, so that the two are distinguishable in the record and an auditor can see which counter refused. Where a reconciliation would exceed the budget, the reconciliation server MUST NOT transmit a projection to the affected register and MUST record query-budget-exhausted as that register's Non-Answer Reason. The reconciliation proceeds and is sealed; it cannot reach a decisive Combined Verdict, by . It is the register that is refused, not the reconciliation: refusing the reconciliation outright would leave no Output in which to record the reason, which is the artefact the requester needs in order to know why it was refused and the regulator needs in order to see that it was. The Pattern Library MUST include a repeated-narrowing pattern so that the Adversarial Pre-Transmission Test detects the sequence rather than only the event. A register cannot apply its own statutory access regime to a requester it cannot see. Where a Bilateral Register Agreement requires it, the Per-Register Claim Projection MUST carry the Requester-Binding Class, which discloses the class and not the principal.

Budget Exhaustion as a Suppression Channel places a reconciliation driven to query-budget-exhausted or subject-ceiling-exhausted outside the reproducibility requirement, because the budget is accumulated state rather than an enumerated input. That carve-out is a suppression channel and is recorded here as one. Any non-answering register makes a decisive Combined Verdict unreachable (). An operator that wishes to prevent a particular reconciliation from reaching a decisive verdict can therefore record query-budget-exhausted against one register, and an auditor replaying the enumerated inputs is required not to treat the divergence as a determinism failure. The reason is server-observed under , so no register signature contradicts it. Two mitigations are available and neither is adopted here. Publishing the budget counter and interval boundaries beside the refusal would let an auditor distinguish exhaustion from suppression -- and would tell every requester how much third-party interest a subject has attracted, and exactly when to exhaust the counter so that no other party obtains a decisive verdict, which is a worse disclosure than the one it cures. Requiring a register-signed acknowledgement of each charge against the budget would remove the server's discretion, at the cost of a round trip to every addressed register on every refused reconciliation, including the ones the budget exists to avoid making. The per-subject ceiling of is the stronger of the two channels, because it is a counter several principals share: an operator need not fabricate anything, only decline to reserve enough of it. requires the reserve to be partitioned per principal for that reason, and the residual is that the size of the reserve is a deployment choice this document does not bound. A deployment concerned with either channel should bound it contractually: the budget, its interval and the audit right over the counter are all declared in the Bilateral Register Agreements, and an Audit Identity under can be given the counter state directly. That is an out-of-band remedy and it is stated as one.

Pattern-Library Integrity The Adversarial Pre-Transmission Test gates onward transmission. The Pattern Library MUST be bound to a Pattern-Library Commitment Hash. Any modification to the Pattern Library MUST produce a new Pattern-Library Version Identifier, and the Adversarial Pre-Transmission Test MUST be re-executed against the new library before the change takes effect.

Agent Impersonation and Friend-or-Foe Integrity The Agent Friend-or-Foe Determination is the mechanism by which ARP resists reconciliation initiated by an agent impersonating a principal. The determination MUST default to ENEMY: absence of a verifiable identity, an expired or revoked signature-agent key, a failed HTTP Message Signature verification, or a Verified Principal Credential that does not validate MUST all yield an ENEMY classification. The server MUST NOT infer friendliness from network origin, User-Agent string, or any self-asserted identifier, as these are trivially forgeable. Where an ENEMY requester is permitted for advisory reconciliation, the resulting Reconciliation Output MUST NOT carry a decisive verdict binding, and the Settlement-Layer Ledger entry MUST record the requester-binding class the gate determined -- agent-unverified where no verifiable identity was presented, or agent-key-verified where a key verified and the asserted principal was not corroborated -- so that downstream reliance is aware no accountable principal was established and can still tell the two apart.

Bilateral-Register-Agreement Drift Each Bilateral Register Agreement carries an Agreement Hash. Each Partial Attestation includes a reference to the Agreement Hash under which it was issued. Agreement drift is detectable by comparison of agreement-hash references across Partial-Attestation batches. Reconciliation MUST be suspended for an addressed register whose Agreement Hash deviates from the hash committed at the start of a reconciliation event. A suspension under this section ends when the two parties have agreed a new Agreement Hash under and the reconciliation server holds it as the hash it commits at the start of the next reconciliation event, from which event the register is addressable again. A suspension arising instead from the irreconcilable head statements of ends only when the Register Operator that refused further projections states, under the read key of item 22 of , that the discrepancy is resolved. No other event ends either, and a deployment MUST NOT treat the passage of time as ending one.

Replay Defence Each Partial Attestation MUST carry a Freshness Timestamp. The reconciliation server MUST verify the Freshness Timestamp against a freshness window declared in the Bilateral Register Agreement. The window is measured backward from the instant the reconciliation server received the Partial Attestation. An attestation is fresh where its Freshness Timestamp is no earlier than that instant less the declared window and no later than 60 seconds after it, and a Freshness Timestamp further in the future MUST be treated as stale. A window with no stated reference instant and no stated direction is a test two implementations apply differently to the same attestation, and the register cannot tell which one it will be held to. This document states the reference instant and direction for the witness observation window of and did not state them here. Stale Partial Attestations MUST be rejected, and the rejection MUST be recorded in the Reconciliation Output under with the Non-Answer Reason attestation-stale and a freshness-stale divergence axis attributed to that register. A signed agent request under MUST additionally carry a nonce and created/expires parameter set that requires, so that a captured signed request cannot be replayed to initiate a fresh reconciliation.

The Clocks a Response Freshness Check Is Decided Across bounds the response-time of a read response in both directions against the reader's receipt of it, because the two values are produced on two clocks nothing in this document synchronises. The backward bound is the declared tolerance, floored and capped in item 26 of ; the forward bound is a fixed sixty seconds. A deployment applying the tolerance as a one-sided test admits a response stamped ahead of the reader's clock, and a server whose clock runs fast is then indistinguishable from one stamping ahead deliberately, which is the case the forward bound exists to separate. A deployment declaring a tolerance below the transit and clock disagreement between the two parties rejects every honest response, which is why item 26 carries a floor as well as a ceiling. bounds the reconciliation server against the register's clock and the created parameter of bounds the server against the requester's. Both run toward the server; this is the return direction, and it is the one earlier revisions left unstated. All three bound a party against another party's clock over a message it has just received, all three differ in their backward bounds -- a declared window in , three hundred seconds in , a declared tolerance here -- and all three fix the forward bound at sixty seconds, that being the direction in which none of them has anything but the other party's word. The witness observation window of bounds a fourth pair of clocks, the witness's against the reconciliation server's, over an artefact published once per interval rather than over a message in flight. Its backward bound is sixty seconds and its forward bound is the greater of sixty seconds and twice the notarisation interval, so sixty seconds is the floor in both directions here too and the interval only ever widens the window.

Where Head-Consistency Evidence Comes From requires Head Consistency Statements from the witnesses' own origins, and requires the linkage chain between two heads from the same origins under . The two are one requirement about one property. A relying party that has only the first has not satisfied the second branch at all, and holds evidence under the first branch alone, which reaches exactly the head a response names and no head above it. A Statement obtained from the party it is evidence about is that party's own selection, countersigned. A linkage chain obtained from that party is that party's chain, and the reason is stronger than selection: a relying party cannot recompute any value in a linkage array, because a Signing Input Digest is taken over a Sig_structure and a Self-Entry Hash over the entry array, and the array carries neither preimage. Every test the chain condition performs is therefore an equality between two values the same party supplied, which is not evidence about that party. Anchoring the ends does not repair it: the lower anchor is the response's own claim, and the upper anchor is a Self-Entry Hash, which is not a position the chain reads. sets out that arithmetic in full. The operational consequences follow from and and are gathered rather than restated here. A witness whose origin is unreachable contributes nothing. A witness whose Segment series does not reach the head its Statement covers contributes nothing to the second branch, though its Statement still serves the first, where it covers the head a response names exactly. A witness that has equivocated between two Segments contributes nothing at all. And the property the Segments deliver is append-only rather than absolute, for the reason sets out: a witness records what the service served it, so the assurance is that an interval a witness has covered cannot afterwards be rewritten, and its strength in any deployment is the diversity of the Witness Set and the frequency of observation.

Post-Quantum Migration The Cryptographic-Primitive-Upgrade Path is the mechanism by which ARP deployments migrate to post-quantum primitives. ML-KEM-1024 is RECOMMENDED for the claim-encryption primitive class. ML-DSA-65 is RECOMMENDED for the partial-attestation-signature and sealing-signature primitive classes. Implementations MUST declare their chosen post-quantum primitives in the Bilateral Register Agreement.

Side-Channel Considerations The disclosure model as a whole, and the residual risks this document accepts, are set out in . Per-register projection narrowing is observable to the addressed register through the Projected Predicate. Implementations MUST NOT use narrowing patterns to fingerprint individual subjects. The Predicate Taxonomy SHOULD be designed such that the set of permitted narrowings is small enough that narrowing observation does not materially weaken subject privacy.

Signature Malleability and Artefact Identity A digest taken over a signed artefact as served identifies that artefact only where the signature has one valid encoding, and not every primitive this document admits has that property. For ECDSA, a signature (r, s) and the signature (r, n - s), where n is the order of the curve's base point, both verify against the same key over the same message. No specification prohibits it: Section 4.1.4 of SEC1 v2.0 and Section 6.4.2 of FIPS 186-5 range-check r and s only, and Section 2.1 of constrains neither. The substitution follows from the verification equation and falls outside every check any of the three imposes. No specification is violated and nothing is forged: the signing authority is identical in both encodings, and a party holding no key can produce the second from the first while it is in transit. Measured over two hundred randomly generated P-256 keys and ES256 signatures, two hundred substitutions verified and two hundred changed the enveloped bytes. EdDSA is not exposed to this substitution. Section 8.4 of puts the check that the decoded S is less than l inside verification, so an attacker holding an Ed25519 or Ed448 signature cannot derive a second byte-string that verifies over the same message under the same key. That is a non-malleability property and not a claim that only one byte-string can ever verify: Section 5.1.7 of leaves cofactored and cofactorless verification optional, so conforming implementations can differ at the margin. A deployment that declares only EdDSA signature primitives under item 2 of is therefore not reachable by this. Nothing in this document requires that, and a deployment declaring an ECDSA primitive is conforming, so the constructions and not the primitive choice are where this is addressed. Every digest in this document that identifies or chains a signed artefact is accordingly a Signing Input Digest, or has its embedded signatures replaced by one. Those are the Prior-Entry Hash of , the Post-Seal Evaluation Record Hash of , the Merkle leaf of , the authority-reference digest of in its tagged-transparency form, the Reconciliation Hash of , and -- reached through the Reconciliation Hash rather than named beside it -- the authorising operator's signature in the Override Record of . The sixth was found after the first five had been repaired, and the way it was missed is worth stating rather than quietly corrected. The first sweep looked for digests taken over signed artefacts, found the Reconciliation Hash embedded a register signature, and repaired that. The Override Record is a signature made by a third party -- the authorising operator, deliberately not the server, under -- travelling to the server over a channel the server does not control, and sitting in a field the Reconciliation Hash preimage carries. It failed no test that was applied to it; no test was applied to it. An implementation MUST therefore apply the rule of over the class rather than over the list above: in any preimage this document defines, every signature made by a party other than the party computing the digest is replaced by its Signing Input Digest. A specification that enumerates the carriers is correct until someone adds a field, and correctness that expires on the next revision is not the property this section exists to establish. The Sig_structure excludes the signature by construction, which is why this is total where a low-S canonicalisation rule is partial -- low-S removes one encoding from a set with more than one member, while the signing input has one value for one signing act however many encodings of the signature exist. The Reconciliation Hash is the one worth naming separately, because excluding the Sealing Signature is what an earlier revision did and it is not sufficient. A Reconciliation Output embeds a register signature in each Query Binding Record and in each Non-Answer Statement of , so its preimage carried a signature after the sealing one was excluded. The Reconciliation Hash is a field of every Settlement-Layer Ledger entry, and therefore inside the Entry Signature payload and inside the Prior-Entry Hash, so leaving it exposed would have reintroduced at one remove exactly what fixing the Prior-Entry Hash removed. The Self-Entry Hash of nulls the signature position and was already outside it. The consequence of getting this wrong is not a forgery and is easy to misdiagnose as one. A reader served a substituted entry computes a Prior-Entry Hash that does not match the following entry's, and concludes the chain is broken when the operator equivocated about nothing. Under a substituted Partial Attestation makes a verifier refuse a valid inclusion proof for the same reason. Both are failures of verification rather than of authenticity, and a deployment that reports them as detected tampering will be reporting something that did not happen.

Artefact Identity Across a Change of Signature Algorithm establishes that a digest over a signed artefact as served identifies that artefact only where the signature has one valid encoding, and it names EdDSA as the primitive not reachable by the substitution. That exemption is real, and it is temporary. A deployment planning a migration to post-quantum signatures should know which of those two facts it is relying on. The substitution asks what a party holding no key can do to an artefact in transit. A registration protocol has to answer a narrower question first, and one that does not involve an adversary at all: how many valid enveloped byte-strings exist over one signing input when the same signer signs the same input more than once. Measured over two hundred ordinary signing operations per primitive, one key and one signing input each, with every reported value recovered by decoding the served envelope rather than reusing the locals that were signed:

Signature primitive	Distinct signing inputs	Distinct enveloped byte-strings
Ed25519	1 of 200	1 of 200
ECDSA P-256	1 of 200	200 of 200
ML-DSA-65, hedged	1 of 200	200 of 200
ML-DSA-65, deterministic	1 of 200	1 of 200
Ed25519 with a parallel ML-DSA-65 leg	1 of 200	200 of 200

Three consequences follow, and the third is not addressed by any document this one is aware of. The Signing Input Digest is stable on every primitive measured, including those whose envelopes are all distinct. This is the property already relies on, and the table establishes that it does not depend on the primitive. A construction bound to the signing input survives a change of algorithm; a construction bound to the enveloped bytes does not. The enveloped byte-string is a stable identifier on Ed25519 because of , not because of anything in COSE or in this document. Section 5.1.6 of derives the per-signature nonce from a hash of the private key prefix and the message, so one key over one message yields exactly one signature. That is a property of one primitive. A deployment that declared only EdDSA under item 2 of and inferred from that its enveloped digests are stable has inferred correctly, and the inference expires the moment a second signature leg is added. A parallel composition of Ed25519 with ML-DSA-65 over one signing input produced two hundred distinct byte-strings from two hundred signing operations, while the Ed25519 leg alone produced one. Composition does not preserve the determinism of its most deterministic member. It cannot: the composed artefact is unique whenever any member is. Two conforming ML-DSA-65 signers disagree about whether the enveloped byte-string is stable, and the artefact does not record which one produced it. specifies both hedged and deterministic signing. Both produce signatures that verify against the same public key, and recommends hedged signing as the safer default in all environments, on fault-injection grounds that this document does not dispute and does not attempt to weigh against anything here. The consequence for artefact identity is unremarked rather than contested: the recommended mode is the mode under which one signing input has an unbounded family of valid envelopes, the selection between the two modes appears nowhere in the protected header or anywhere else in the signed object, and a relying party holding one envelope therefore cannot determine whether a second envelope over the same input would be the same bytes. A registration protocol that identifies an entry by its enveloped digest is, under ML-DSA, identifying something whose stability is decided by a signer-side flag it cannot observe. A low-S canonicalisation rule does not reach any of this, and its reach shrinks rather than holds. states why it is partial for ECDSA: it removes one encoding from a set with more than one member. Past the classical boundary it is not partial but inapplicable, because ML-DSA signatures carry no s value to canonicalise. A deployment defending enveloped-digest identity by mandating low-S is defended for exactly as long as it signs with ECDSA. An implementation MUST NOT treat the digest of an enveloped signed artefact as an identifier for the claim the artefact carries, and MUST use the Signing Input Digest of for that purpose, in any construction this document defines. Where a Reconciliation Agreement declares a signature primitive under item 2 of , it MUST additionally declare, for any primitive admitting more than one signing mode, which mode the signer operates. That declaration is a statement about a signer and not about an artefact, and a relying party that requires the distinction has no other place to obtain it.

Declared Trade-offs Several properties this document would like to hold cannot hold together. Where that is so, the document chooses, and this section is the list of the choices in one place, so that a reader can find what was given up without reading for it. The discipline is worth stating on its own. A specification that wants two incompatible properties has three options: claim both and be wrong somewhere a reader has to find; weaken both until the conflict disappears and deliver neither; or take the conflict as irreducible, choose, and say where the loss went. The third is the only one that leaves a reader able to reason about a deployment. What makes it work is that the loss is located rather than distributed: a reader who knows exactly which property was surrendered, and where, can compensate for it, and a reader told that everything holds cannot.

Wanted	Also wanted	Given up	Stated in	What a reader can check instead
A chain between two heads a relying party can check	A chain the responding service did not write	Absolute rewrite detection; what holds is append-only over intervals a witness has covered		How many independent witnesses cover the interval, and how often each observes
Reproducible output from enumerated inputs	Uniqueness per reconciliation	Exact identity, for three fields		Every other field is identical; the three are carved out by name
Erasure of a subject's data	An append-only record	Permanence of Output content		No chain depends on content; a digest whose preimage is gone is still a valid chain element
A schema upgrade with no flag day	Telling withheld from never-defined	The upgrade; absence is encoded, not omitted		Array length is fixed by Entry Type, so a short array is a defect and not a version
A chain stable under re-encoding	A verifier-side test that an entry was signed once	The test		The obligation remains and is examinable by an auditor; a re-signature under a different key still moves the chain
Digests unguessable from outside	An auditor who can recompute them	Recomputation without the blinding value		Consistency across two reads, and nothing more, which that section now says
A register recognising a returning counterparty	A requester unlinkable from one reconciliation to the next	Unlinkability, by default		The deployment may substitute a fresh element each time; the choice is declared
One interoperable register leg	Sovereign registers keeping their own interfaces	The common leg		Every leg is declared in an Agreement whose hash is committed to
A regulator reading a redacted entry	That regulator verifying the entry's chain	Chain verification under redaction		Redacted fields are null in place, so the length is intact and an unredacted read is available
Errors that tell a requester what went wrong	Endpoints that are not existence oracles	Distinguishing errors, on the read path		The commissioning path distinguishes them and pays for it in rate limit and access log
Coverage measured without cost	Probes a register cannot tell from real work	Free measurement		A probe consumes a real budget against a real register, which is what makes it uncountable by the operator
A quorum proving observer independence	A test a verifier can actually run	Proof of independence		Distinct declared parties and distinct keys, both mechanically checkable

Two things follow from having written this table that were not obvious before writing it. The first is that most of the losses are stated limits rather than open defects, and the difference is whether a reader can compensate. A limit a reader knows about is an input to that reader's decision; a limit it does not know about is a false belief. This document has repeatedly found that its own worst errors were sentences claiming a property it did not have, rather than missing properties honestly described, and the table is the form that makes the distinction hard to lose. The second is that a row can be retired by invention. Two rows that stood in earlier revisions no longer do: the falsifiability of a sweep against its operator, which was traded away and has been bought back by anchoring the Policy Parameters Document; and the verifiability of the sweep counts, which was conceded as an assertion and is now an accounting identity against the Ledger. A trade-off is a statement about the mechanisms available at the time it was made, not a law, and a list of them is also a list of what to attack next.

Privacy Considerations This protocol operates over beneficial-ownership registers, corporate registries, consolidated sanctions lists and customs records. Its subject is almost always a party that is neither the requester nor a recipient, and that is not told a reconciliation about it occurred. The disclosure model has two artefacts and one division. A Reconciliation Output is confidential to its Audience Set and carries subject references, register-signed attestations and principal identifiers; the Settlement-Layer Ledger is broadly readable and carries digests, register origins and structural metadata. states the division and the rules that rest on it. What the witness artefacts disclose. obliges a witness to serve Segments to any party without authentication, where the same linkage arrays are readable from the reconciliation server only by an entitled requester under a rate limit. That is an entitlement change and it is made deliberately: an artefact obtainable only from the party it is evidence about is that party's selection, so head-consistency evidence has to be world-readable to be evidence at all, which is the choice already made for Head Consistency Statements. What it adds is the Prior-Entry Hash and the Signing Input Digest of each entry alongside the Self-Entry Hash. All three are digests over signed artefacts rather than over subject data, none is a low-entropy preimage of the kind the Deployment Blinding Value of exists to protect, and the interval a Segment covers is bounded above by a head already publishes unauthenticated, so the live head oracle guards against is not reintroduced. Two residues follow and are recorded here rather than left to be inferred. The first is that the linkage values of every covered entry become readable without entitlement, where rate limits the equivalent read at the reconciliation server and a witness serving Segments is not rate limited by this document. The entry count and the write rate over time are not part of that residue: publishes a contiguous head unauthenticated once per interval, so both follow from differencing two published heads and were public already. What is new is the per-entry chain shape below a published head. The second is the allowance makes for a witness principal. The holder of a key can learn, from the number of ranged linkage reads admitted to it, that the key sits in a Witness Set some Bilateral Register Agreement the deployment holds declares, which is a wider set than the effective Witness Set the Policy Parameters Document of already publishes. The disclosure is membership of a union rather than of an intersection, it is available only to the holder of the key in question, and it is the price of a publication obligation a rate limit would otherwise void. What is protected. The Deployment Blinding Value of keeps the Claim Hash and the Policy-Version Hash from being inverted by exhaustive search over their low-entropy preimages, which is what stops a Ledger reader recovering the subject and the commissioning principal. Entitlement follows the Audience Set, so possession of an Output is not authorisation to learn what happened to it afterwards. Enrolment under means a requester cannot direct an Output at a party that has not agreed to receive one. The per-principal query budget of bounds recovery of a register record by repeated querying. Read responses are rate-limited and logged, and the log is not on the Ledger, because a Ledger that recorded reads would disclose the pattern of interest in a subject to everyone entitled to read it. What is not. A subject has no standing in this protocol: it is not notified, it cannot object, and it cannot learn that it was reconciled. That is a deliberate property of a sanctions-screening protocol and a real cost, and a deployment operating where subject rights attach should provide for them outside this document. An Audience Member learns the subject, the predicate and every register's answer; the audience constraint of lets a register cap how many such parties there may be, and the register cannot verify that the cap was enforced. Notarising an Output under places it in a log whose retrieval is by EntryID, and a deployment for which that is the wrong disclosure should not notarise. The Ledger Head Statement is unauthenticated and carries a contiguous sequence number, so it discloses the deployment's size and approximate rate at the notarisation interval. An Audit Identity under reads every Output of every reconciliation addressing its register irrespective of Audience Set, and each register declares one, so a deployment's disclosure surface grows with the number of registers it addresses. An Override Record names an authorising operator in the clear inside the Output. records a further residual risk, and the projection-narrowing channel.

Against the threat model of RFC 6973 Taking the threats of Section 5 of in turn, and stating the residual rather than the mitigation where there is one. Surveillance and correlation. Every digest that could otherwise correlate a subject across deployments is blinded: a Claim Hash cannot be recomputed outside the deployment that produced it and equality of Claim Hashes across deployments is not a comparison that can be made at all. Within a deployment, correlation is by design -- the Ledger index is a stable function of the claim, which is what makes retroactive re-evaluation possible -- so a Ledger reader entitled to nothing else still learns that some subject was reconciled repeatedly, and how often. That residual is inherent in an append-only index and is not closed here. Identification. The Ledger carries no Subject Identifier and no Subject Reference. Those travel to the addressed registers, which is unavoidable in a protocol that asks a register about a subject, and into the Reconciliation Output, which is confidential to its Audience Set. Secondary use and disclosure. A reconciliation server MUST NOT write a Subject Identifier, a Subject Reference, an Applied-Parameter Set or any register-record field to the Settlement-Layer Ledger, and MUST NOT include one in any artefact it notarises into a Transparency Service. Notarisation under places the sealed Output into an append-only log operated by a third party, and a sealed Output carries Subject References inside its Query Binding Records. Notarisation of an Output is a MAY and MUST NOT be performed where the deployment's subjects have not been accounted for in that disclosure. The Ledger Head Statement, the Evaluation Sweep Statements and the Policy Parameters Document carry no subject data and are the artefacts this document requires to be notarised. Exclusion. The subject is not told, cannot object and cannot learn that it was reconciled. This is stated above as a deliberate property and it is the sharpest privacy cost the protocol imposes. It is restated here because names exclusion as a threat in its own right and a document that lists its mitigations and passes over the one threat it does not mitigate is reporting selectively.

Erasure and rectification against an append-only record A jurisdiction in which a subject may require erasure or rectification of personal data is in direct tension with a Ledger this document requires to be append-only and with a Transparency Service it requires to be outside the operator's control. That tension cannot be resolved by a protocol mechanism, and this document does not claim to resolve it. What it can do is bound what has to be erased, and that is a design obligation rather than a remark:

• No personal data is written to the Ledger, per the rule above. What the Ledger carries about a reconciliation is digests, register Authority Origins, verdict values and structural metadata. An erasure obligation over the subject's data therefore falls on the Reconciliation Output and the register correspondence, both of which are held by the deployment and both of which have a retention period.
• A retracted or rectified verdict is expressed by supersession and not by deletion. appends a continuation-supersession entry and notifies the affected regulators. The superseded Output remains identified by its Reconciliation Hash and its content may be destroyed at the end of its retention period without breaking any chain, because no chain hashes the Output's content: the Ledger commits to the Reconciliation Hash, and a digest whose preimage no longer exists is still a valid chain element. This is the property that makes erasure implementable at all, and an implementation MUST NOT introduce any construction that hashes Output content into the chain.
• A deployment that has notarised an Output cannot erase it, because the Transparency Service is required not to be under the operator's control. That is the reason notarisation of an Output is optional and is now prohibited where the disclosure has not been accounted for.

A deployment operating under an erasure regime should treat the retention period of as the erasure horizon for Output content, and should not notarise Outputs. This document states that as guidance and not as a requirement, because the obligation arises outside it and its shape differs by jurisdiction. What is normative is the constraint that makes any of it possible: personal data does not enter the append-only record, and nothing in the chain depends on the continued existence of the content that could be erased.

IANA Considerations This document requests IANA to register the following:

• Four COSE header parameters in the COSE Header Parameters registry, values to be assigned by IANA:
  • arp-bilateral-agreement-hash (value TBD)
  • arp-policy-version-hash (value TBD)
  • arp-source-data-version (value TBD)
  • arp-witness-identifier (value TBD)
  arp-witness-identifier is a CBOR text string carrying the identifier of the Witness Entry whose key signed the artefact, and is used by and ; arp-policy-version-hash is a CBOR byte string; arp-bilateral-agreement-hash is a CBOR array of byte strings; arp-source-data-version is a CBOR array of two-element arrays, each of a list name and that publisher's state identifier, as constructs it. Each MUST appear in a protected header and MUST NOT appear in an unprotected one: every one of them is a commitment a verifier relies on, and a commitment a signature does not cover is not a commitment. arp-policy-version-hash and arp-bilateral-agreement-hash are used by ; arp-source-data-version is used by .
• Two COSE Key common parameters in the COSE Key Common Parameters registry, values to be assigned by IANA: arp-key-status (value TBD), a CBOR text string of active, retired or revoked; and arp-key-validity (value TBD), a two-element CBOR array of the not-before and not-after times, or a three-element array whose third element is a revocation time where the entry's arp-key-status is revoked, each in the form of . requires both on every key it publishes, and a key parameter used normatively and never registered is a parameter no other implementation can read.
• A registry of ARP Divergence-Axis values, registration policy Specification Required, initially containing the descriptors enumerated in the Divergence Axis definition of . Each entry MUST record whether the axis is register-attestable or server-recorded, a distinction eight normative sections depend on and which is otherwise carried only in prose. The designated expert MUST refuse a registration that does not state it.
• A registry of ARP Non-Answer Reasons, registration policy Specification Required, initially containing the values enumerated in . Each entry MUST record whether the reason is register-attested or server-observed, which determines whether a Non-Answer Statement signed by the register is required; the initial entries are recorded as states. A Non-Answer Reason is not a verdict; the designated expert MUST refuse a registration that could be combined by the Verdict Arithmetic, and MUST refuse a register-attested registration that does not state what the register signs over.
• A registry of ARP Excluded-Range Reasons, registration policy Specification Required, initially containing outside-retention, where the range predates the retention period of ; not-in-scope-of-trigger, where no entry in the range carries a value the trigger reached; and superseded-in-range, where every entry in the range was already superseded by an earlier sweep whose Statement is named. A registration MUST name a condition a reader holding the Ledger can check for itself, and the designated expert MUST refuse one that can only be confirmed by the operator asserting it, since a disposition a reader cannot test returns the range to the state that having a disposition was meant to leave behind.
• A registry of ARP Subject Mapping Descriptors, registration policy Specification Required, initially containing identity, profile-declared and agreement-declared, defined in . A registration MUST specify a transformation that is a function of the Subject Identifier and of declared terms alone. The designated expert MUST refuse a registration whose transformation takes any input the reconciliation server chooses at reconciliation time, since a descriptor naming server discretion records that the discretion was exercised and not what it did.
• A registry of ARP Verification Outcomes, registration policy Specification Required, initially containing the values enumerated in . A registration MUST name a condition a verifier can reach mechanically, and MUST state whether reaching it is evidence of equivocation by the serving party, evidence of a transport or encoding difference, or neither. The designated expert MUST refuse a registration that does not state which, because the distinction between an operator that equivocated and an artefact that was re-encoded in transit is the one this registry exists to carry.
• A registry of ARP Post-Seal Evaluation Qualifiers, registration policy Specification Required, initially containing notarisation-incomplete and attribution-indeterminate, defined in . A registration MUST identify a condition arising after a Reconciliation Output is sealed; the designated expert refuses a registration that qualifies a verdict, which belongs in the Divergence-Axis registry.
• A registry of ARP Register Data-Format Profile identifiers, registration policy Specification Required, initially containing arp-profile-bods, arp-profile-corporate-org, arp-profile-customs-wco and arp-profile-sanctions-consolidated, defined in . Identifiers beginning x- are reserved for bilateral use and are not registered. A registration MUST state the dated vocabulary in which permitted predicates are expressed where it names one and state that it names none otherwise, the relation corresponding to taxonomic narrowing for each branch of its predicate space, and the parameters a Bilateral Register Agreement declaring it must supply. The designated expert refuses a registration that defines any means of transporting register records, that declares more than one parent relation applicable to a single predicate, that names a vocabulary without pinning its version, or that fixes in the profile a parameter varying between registers using the same format.
• A registry of ARP Aggregation-Method Descriptors, registration policy Specification Required, initially containing hash-linkage-conjunction, hash-linkage-disjunction, hash-linkage-threshold-count and hash-linkage-source-class-quorum: the aggregation mode of joined to the Verdict-Arithmetic operator it sequenced. A registration naming a new aggregation mode MUST specify that mode's construction; the descriptor is a signed Ledger field and a mode with no construction gives it no meaning.
• A registry of ARP Retroactive Evaluation Triggers, registration policy Specification Required, initially containing pattern-library, policy-version, source-data-version, credential-revocation and register-record-correction, defined in . A registration MUST name an event whose occurrence and time a party outside the reconciliation server can establish, or state plainly that it cannot, since the falsifiability of turns on it.
• A registry of ARP Override Grounds, registration policy Specification Required, initially containing operational-continuity, pattern-false-positive and statutory-obligation, defined for use in the Override Record of the Adversarial Pre-Transmission Test. A registration MUST state the circumstances in which the ground is available and MUST NOT admit a ground that could be asserted of every override, which would return the field to free text.
• A registry of ARP Re-Typing Grounds, registration policy Specification Required, initially containing bounded-depth-not-closure, declared-not-determined, threshold-divergence and projection-broadened, corresponding to the four grounds of .
• A registry of ARP Verdict-Arithmetic operators, registration policy Specification Required, initially containing conjunction, disjunction, threshold-count and source-class-quorum, defined in . A registration MUST state the operator's result as a total function of the multiset of contribution values and the operator's declared parameters, and MUST state whether it admits partial-match, on which turns.
• A registry of ARP Ledger Entry Types, registration policy Specification Required, initially containing reconciliation, continuation-notarisation, continuation-post-seal-record and continuation-supersession, defined in . Entry Type values are CBOR text strings. A registration MUST enumerate the fields an entry of that type carries in addition to the fields every entry carries, MUST state their order, since the Self-Entry Hash is taken over that order, and MUST state each field's value type and whether it is conditionally absent and on what condition. The designated expert MUST refuse a registration whose type restates a field already carried by the reconciliation entry it continues, and MUST refuse any type other than reconciliation that records a reconciliation rather than a fact arising after one was sealed. The initial registrations are those of , with these value types. Every hash is a 32-octet CBOR byte string; every sequence number is a CBOR unsigned integer; every timestamp is a CBOR text string in the form of ; every Entry Type is a CBOR text string; the Addressed-Registers Identifier Set is a CBOR array of text strings, each an authority origin, sorted in bytewise lexicographic order of its UTF-8 encoding; the Aggregation-Method Descriptor and the Requester-Binding-Class Descriptor are CBOR text strings, the first drawn from the ARP Aggregation-Method Descriptors registry and the second from the four classes of the Requester Identity Binding and Agent Friend-or-Foe Gate section; the Override Indicator and the Material-Change Indicator are CBOR booleans; the Transparency Service Identifier is a CBOR text string carrying an authority origin; the EntryID is a CBOR text string as returns it; an HTTP status code is a CBOR unsigned integer; and every Entry Signature is a COSE_Sign1.

Well-Known URIs Eight entries are requested in the Well-Known URIs registry of . For each, the change controller is the IETF, the status is permanent, and the specification document is this document.

URI suffix	Defined in	Path syntax below the suffix
arp-sealing-keys		/{kid}, where {kid} is a JWK thumbprint, returns that single key
arp-register-keys		/{kid} as above
arp-operator-keys	the Adversarial Pre-Transmission Test	/{kid} as above
arp-authorised-origins		none
arp-ledger-head		none
arp-policy-parameters		none
arp-head-consistency		none; served by a witness on the Authority Origin of its Operating-Party Identifier
arp-witness-linkage		/{n}, where {n} is an Entry Sequence Number, returns the single Segment covering it; the bare suffix returns the most recent; served by a witness on the same origin as arp-head-consistency

Media types Fourteen media types are requested, registered under the template of . For each: the type name is application; there are no required and no optional parameters; the encoding considerations are binary, save for the +json type, which is 8-bit UTF-8 text; the security and interoperability considerations are those of this document; the published specification is this document; the intended usage is COMMON; the change controller is the IETF; the applications that use the type are ARP reconciliation servers, registers, regulators and relying parties; there are no restrictions on usage; the author is the author of this document and the contact address is the one on its front page; there are no deprecated alias names, no magic numbers and no customary file extensions; and fragment identifier considerations are those of the structured syntax suffix where one applies -- Section 3.1 of for +json -- and are otherwise none, no fragment identifier syntax being defined for the +cbor and +cose forms.

Subtype	Carries	Defined in
arp-reconciliation-request+cbor	a request commissioning a reconciliation
arp-remediation-advisory+cbor	a Remediation Advisory	the Adversarial Pre-Transmission Test
arp-sovereign-re-notification+cose	a Sovereign Re-Notification
arp-sealed-reconciliation-output+cose	a Reconciliation Output under its Sealing Signature, whether delivered directly or nested in a SCITT Signed Statement
arp-policy-parameters+cose	a Policy Parameters Document
arp-post-seal-evaluation-record+cbor	a Post-Seal Evaluation Record
arp-reconciliation-output+json	the RFC 8785 payload of the Verifiable Credentials form
arp-ledger-head+cose	a Ledger Head Statement
arp-read-response+cose	a signed read response
arp-evaluation-sweep+cose	an Evaluation Sweep Statement
arp-key-set+cose	a signed COSE Key Set or an Authorised-Origin Document
arp-head-consistency+cose	a Head Consistency Statement
arp-witness-linkage+cose	a Witness Linkage Segment
arp-probe-commitment+cose	a Probe Commitment

Acknowledgments This document benefits from the SCITT Architecture , the SCITT Reference APIs , COSE Receipts , the RATS Architecture , HTTP Message Signatures , and the Web Bot Auth HTTP message signature protocol . Named findings, because a specification improved by review should say by whom. Songbo Bu established that the indistinguishability requirement of could not be satisfied as -02 stated it: the response profile of binds each response to its request and its serving instant, so two responses cannot be byte-equal, and a conformance rule demanding that they be would fail every conforming implementation. The normalised observation in , its enumeration of HTTP metadata and cache behaviour, and the separation of the deterministic requirements from any statistical timing claim are his design, contributed as an executable vector class. Steven Mih established that the empty-result contradiction of is conditional on the reader and any later observer having been served one chain, and that under the fork admits it may be opportunistic to detect, an absence assertion can stand uncontradicted indefinitely. The boundary now stated in is his finding. He also confirmed, against three independent drafts, that the deterministic encoding requirements relied on here are those of Section 4.2.1 of and not those of Section 9 of . Iman Schrock established, with Anton Sokolov, that a content digest cannot serve as a correlation key across independently produced descriptions of one act. He then established that the earlier repair was itself imprecise: declares required and optional fields per action type and marks no field as a correlation key, so the selection belongs to the profile. The requirements in to pin the action type and version, the selected field and its normalisation and comparison rules, and to require that the selected field be present in the Canonical Claim so that the Claim Hash commits to it, are his, substantially as he drafted them. Walter Hawkins established that the falsifiability condition of is bounded by observer diversity rather than by any stronger single-log property: head evidence obtained from the responding service cannot bound a fork, because a fork at disjoint sequence numbers is invisible from a single vantage by construction and the vantage is what is in question. Naming the independent observer, and the ordering of witness countersignature over independently anchored head digest, is his. Tiago Pinto established that the obligation to answer with a signed response carrying a log position belongs on the party making the claim rather than on the party relying on it, and that an unsigned or position-less answer is to be treated as the log not having answered. takes that shape at his argument. Tom Sato's leaf-construction work on Certificate Transparency logs informed the inclusion-proof requirements of , and established that a document defining a Merkle construction without stating its relationship to Certificate Transparency leaves an implementer arriving from RFC 6962 unable to tell whether the two agree. Anton Sokolov established that a digest taken over a signed artefact as served does not identify that artefact under a signature primitive whose encoding is not byte-unique, and that ECDSA is such a primitive without violating SEC1, FIPS 186-5 or . , and the reconstruction of the Prior-Entry Hash of , the Post-Seal Evaluation Record Hash of and the Merkle leaf of as Signing Input Digests, follow from his measurement. Iman Schrock separately established that the digest of a COSE_Sign1 envelope, the digest of its Sig_structure and the digest of the authorization payload inside it are three references a relying party has to be able to hold apart, and that a protocol identifying a registration entry by the first of them forces applications to treat it as the identity of the third. He further established the scope of a low-S canonicalisation rule against that question: low-S enforcement can reject the high-S encoding at a verifier and does not by itself resolve the identity question, particularly where normalisation occurs after an envelope has already been registered. The separation stated in , and its limitation of low-S, are his; what this document adds is the measurement across signature primitives and the observation that the exemption grants to EdDSA does not survive composition with a post-quantum leg. Henri Sirkkavaara established that a document may carry both the sound and the unsound rule at once, each defensible on its own reading, and that the check is therefore to sweep every identity rule in a tree rather than to correct the one that was reported. Applied to this document it found that the Self-Entry Hash of already excluded the signature while the Prior-Entry Hash two paragraphs below it did not. Nenad Vasic established that an inclusion proof whose carried leaf is lifted unchanged from another object's valid proof folds to the correct root under a sibling array that verifies, so that a verifier walking the path before recomputing the leaf accepts a proof bound to bytes it does not hold. The requirement in that a verifier compute the leaf from the object whose inclusion is being proved and use that value as the input to the sibling walk is his, contributed as an executable vector against a third-party corpus.

References Normative References Fraunhofer SIT Bowball Technologies Ltd Microsoft Research The Unicode Consortium Informative References Certisyn, Inc. EMILIA Protocol, Inc. Open Ownership World Wide Web Consortium World Customs Organization United Nations Economic Commission for Europe United States Department of the Treasury, Office of Foreign Assets Control European Union Action State Group, Inc. MyAuberge K.K. EMILIA Protocol, Inc. Independent Tyche Institute Action State Group, Inc. Tyche Institute Cloudflare Google Cloudflare Amazon Cloudflare Oracle

Examples

Example: Three-register Sanctions Reconciliation This example is illustrative and non-normative; register identifiers, values and parties are fictitious, and no bilateral agreement with any named authority is asserted or implied. Suppose a relying party requests reconciliation of the predicate sanctions:any-list-match for subject identifier corp:EXAMPLE:0123456789 against three consolidated sanctions registers. Each Bilateral Register Agreement permits the predicate. The projection function emits identical Per-Register Claim Projections to all three registers. All three return Partial Attestations with verdict no-match. The Aggregation Subsystem operates in Hash-Linkage Aggregation. The Verdict Arithmetic, resolved from policy for the regimes the claim names, is disjunction. The Combined Verdict is no-match. The requester named itself and its compliance department's shared identity in the Audience Set; no addressed register declared an audience constraint, so both are admitted. The reliance interval that policy declares for sanctions: predicates is seven days, so the Reliance Horizon is 2026-05-04T19:47:14Z. The Output is sealed against the current Policy-Version Hash and returned to the requester in the signed read response to the request that commissioned it, over which the requester computes its Reconciliation Hash. The Settlement-Layer Ledger entry comprises:

• Entry Sequence Number: 42
• Entry Type: reconciliation
• Claim Hash: <32 bytes>
• Reconciliation Hash: <32 bytes>
• Entry Timestamp: 2026-04-27T19:47:15Z
• Prior-Entry Hash: <32 bytes>
• Policy-Version Hash: <32 bytes>
• Addressed-Registers Identifier Set: ["https://register-a.example", "https://register-b.example", "https://register-c.example"]
• Aggregation-Method Descriptor: hash-linkage-disjunction
• Merkle Root: <32 bytes>
• Requester-Binding-Class Descriptor: "human-operator"
• Reconciliation Timestamp: 2026-04-27T19:47:14Z
• Source-Reconciliation-Output Identifier: CBOR null -- this reconciliation supersedes none
• Override Indicator: false
• Self-Entry Hash: <32 bytes>
• Entry Signature: COSE_Sign1, Sealing-Key Identifier (https://arp.example, example-sealing-2026-01)

The one absent field occupies its position as CBOR null, so that the array's length is fixed by the Entry Type and the Self-Entry Hash is taken over a determinate encoding. When the sealed Output is registered with a Transparency Service, the EntryID it returns is not written into entry 42, which is already signed; it is appended as a later entry:

• Entry Sequence Number: 57
• Entry Type: continuation-notarisation
• Claim Hash: <the same 32 bytes as entry 42>
• Reconciliation Hash: <the same 32 bytes as entry 42>
• Entry Timestamp: 2026-04-27T19:52:03Z
• Prior-Entry Hash: <32 bytes>
• Transparency Service Identifier: https://ts.example/
• the notarisation outcome: ["entry-id", <the identifier that service returned>]
• Self-Entry Hash: <32 bytes>
• Entry Signature: COSE_Sign1, Sealing-Key Identifier (https://arp.example, example-sealing-2026-01)

Entry 57 carries no Policy-Version Hash and no Addressed-Registers Identifier Set; entry 42 records those and the shared Reconciliation Hash binds them. No register record content is stored on the Ledger in either entry. Had the registration neither completed nor been refused within the polling bound, entry 57 would not exist: the outcome would be a Post-Seal Evaluation Record qualified notarisation-incomplete, pointed to by a continuation-post-seal-record entry, and a later completion -- were the server able to learn of one, which records as an open question -- would be appended as a continuation-notarisation entry later in the sequence. Had the service instead refused registration terminally, the second field would read ["refused", 400]. On 2026-05-06, two days past the Reliance Horizon, the compliance department wishes to rely on the verdict again. Being an Audience Member it presents a signed GET /arp/continuations/{reconciliation-hash}. The server answers 200 with a signed response carrying the ledger head it was served against and, as its result, entry 57 alone. That the result contains no continuation-supersession entry is a signed statement by the server that as of that head there was none -- not merely the absence of one -- and the department retains it. Had it not been an Audience Member the same request would have returned 404, which is also what it would have received had the Reconciliation Hash named nothing at all.

Example: Retroactive Re-evaluation Continuing the illustrative example above: six weeks after that reconciliation, the list register-a.example consults adds the subject as part of a new tranche. That register, on next invocation over the bilateral channel its agreement declares, returns verdict match. The Retroactive Evaluation Subsystem detects the new Source-Data Version the list publisher issued, re-invokes Partial Attestations on the historical reconciliations whose Per-Register Result Set carries a Source-Data Version Identifier from the republished list, identifies the material verdict change, and emits a Sovereign Re-Notification through the Regulator Portal to the regulators whose statutory-regulator-access scope intersects the changed reconciliation. It also emits an Evaluation Sweep Statement recording the trigger source-data-version, the identifier of the list version that triggered it, the policy state applied, the ledger head at the start and end of the sweep, the Examined-Set Root over the Claim Hashes it examined, and the counts examined and materially changed. The compliance department later presents that root and its own Claim Hash to GET /arp/sweeps/{examined-set-root}/inclusion/{claim-hash} and is shown that its reconciliation was in the set the server claims to have examined. Had the server not run the sweep, there would be no Statement covering a list republication whose date is public, and its absence would itself be the finding. The supersession is recorded from both ends. A new Reconciliation Output is sealed against the current Policy-Version Hash and appended as a reconciliation entry whose Source-Reconciliation-Output Identifier is the Reconciliation Hash of the superseded Output. A continuation-supersession entry is then appended against the superseded Output, carrying that Output's Claim Hash and Reconciliation Hash, a Material-Change Indicator of true -- the verdict moved from no-match to match, which is decisive-to-decisive and therefore material -- the Superseding-Reconciliation Hash of the new Output, and the Entry Sequence Number of the entry that records it. The compliance department, an Audience Member of the original Output, presents GET /arp/continuations/{reconciliation-hash} again. This time the signed response carries the continuation-supersession entry. It reads the Superseding-Reconciliation Hash, presents GET /arp/outputs/{superseding-reconciliation-hash}, and is served the new Output -- because a superseding Output inherits the Audience Set of the Output it supersedes, so the party entitled to learn that its verdict changed is entitled to see what it changed to. It verifies the new Sealing Signature, reads the match, and acts. Had the department retained the earlier signed empty response and the server now denied that any supersession existed, the two signed statements by one key would be irreconcilable, which is the point of signing them. A party that is not an Audience Member -- one that was handed the Output by someone who was -- reaches none of this. It may verify the Sealing Signature and read the no-match, which is what makes an Output worth handing on, and it obtains no read, learns of no supersession, and must not treat the verdict as current. Entitlement follows the Audience Set, not the artefact.

Example: Agentic Principal Reconciliation An autonomous agent requests reconciliation of sanctions:any-list-match over HTTP, signing the request under HTTP Message Signatures with a key published in a Web Bot Auth signature-agent card. The reconciliation server verifies the signature (Agent Friend-or-Foe Determination: the agent carries a verifiable identity). That establishes the class agent-key-verified -- the key verified and the asserted principal is so far uncorroborated -- and the Agent-IFF policy for the sanctions: class does not admit a decisive verdict at that class. The server therefore first performs an agent:principal-binding-verifiable reconciliation with Subject Identifier set to the agent's key thumbprint and Attested Value set to the asserted principal org:ACME:operator:jdoe, addressing the ACME organisational directory register and the credential-issuer status-list register. Both return match. The Requester-Binding class is raised to agent-verified with accountable principal org:ACME:operator:jdoe, committed to the Policy-Version Hash, and only then is the sanctions reconciliation performed with a decisive verdict binding. Had either identity register returned no-match with an attested Divergence-Axis Field of agent-impersonation-suspected, the agent would have been classified ENEMY -- a contradicted binding is a stronger signal than an absent one -- and the sanctions reconciliation refused or downgraded to advisory per policy. The distinction is not bookkeeping. Under -02 both states were recorded as agent-verified, so a relying party reading the Ledger entry for the first reconciliation could not tell an agent whose principal had been corroborated against two registers from one that had merely signed correctly.

Example: Divergent Agent-Action Reconciliation This example is illustrative and non-normative. Capsule slots are those of ; see . An autonomous agent is authorised, by a signed CAN capsule, to read from a named evaluation dataset and to write only to a sandboxed result store. During execution the agent's actual conduct, attested by a WHAT capsule produced by the execution environment, includes an outbound network connection to an external host and a write outside the sandboxed store. A relying party submits both capsules to ARP over the agent: predicate branch with a shared subject digest computed over the action. ARP verifies each capsule's signature, projects the authorised scope from the CAN capsule and the actual scope from the WHAT capsule, and reconciles them. The scopes diverge: the actual conduct exceeds the authorised scope. The Combined Verdict is no-match, and agent-action-scope-divergence is recorded in the Server-Recorded Divergence-Axis Set: it is a relation between two capsules and no single capsule producer can attest it, on the same reasoning that makes source-version-skew server-recorded. Because the Agent-IFF policy for this action class requires a decisive match before the action is treated as authorised, the divergent verdict is available as a refusal at decision time -- the reconciliation surfaces the excess while the action can still be refused, rather than after the consequence. The Reconciliation Output is sealed against the Policy-Version Hash and written to the Settlement-Layer Ledger without claim or register content, with requester-binding class agent-verified -- the agent's asserted principal having been corroborated as in the preceding example -- and no register or capsule content disclosed.

Example: Verifiable Credentials Form of an Output This example is the first vector of the conformance class of . The payload below is shown with indentation for reading and folded under . The signed payload is its serialisation, 1,247 octets with no whitespace and members in code-unit order. The hash and key values are those of the published test seed. The COSE_Sign1 protected header, in extended diagnostic notation: { 1: -8, 4: 'VDux_CmeAgi2AvrAFW0bInmtCjMDD9kHOfzia5l81w0', 16: "application/vc+cose", 3: "application/arp-reconciliation-output+json" } The payload: ========== NOTE: '\' line wrapping per RFC 8792 ========== { "@context": [ "https://www.w3.org/ns/credentials/v2", { "@vocab": "https://datatracker.ietf.org/doc/draft-hillier-\ \scitt-arp/vocab#" } ], "credentialSubject": { "addressedRegisters": [ "https://ofac.example.gov", "https://sanctions.example.eu" ], "audienceSet": [ { "id": "https://acme.example.com/operators/jdoe", "verificationMethod": "ui8q-Oh_44_8fBC8GAy1L9256mAf5rFhk\ \au8_M3YL7k" } ], "bilateralRegisterAgreementHashes": [ "bGZZqJQYgwPMmKK8JhsCgjO_qLBBDx2vJWVHo_rY03k", "f9SeSX9aYohdR8ZQESBPAKLgx0DiRCGI9RKhdL6h4m4" ], "claimHash": "DXnYYMYKBOTXl8wyyilXrljSu_xfAHgO8uGsTuLKu_s", "combinedVerdict": "no-match", "policyVersionHash": "AFF2RolekqOQRbkVNzh5WM493yXRFD4PtgFtFA\ \7FcIo", "reconciliationHash": "LLJqwmuxKzSvgqXO2zWYJyB4tEY6tt6NIojRV\ \jPDyfM", "reconciliationTimestamp": "2026-10-14T18:00:00Z", "relianceHorizon": "2026-10-15T18:00:00Z", "requesterBindingClass": "agent-verified", "sealedOutput": { "digest": "wV7R-2vxEC9c7XAWIaMKYht97UvgOjF7vQhXmw9kJTo", "digestAlgorithm": "sha-256", "mediaType": "application/arp-sealed-reconciliation-output\ \+cose" } }, "id": "urn:arp:reconciliation:LLJqwmuxKzSvgqXO2zWYJyB4tEY6tt6N\ \IojRVjPDyfM", "issuer": "https://arp.example.org", "type": [ "VerifiableCredential", "ArpReconciliationOutput" ], "validFrom": "2026-10-14T18:00:00Z", "validUntil": "2026-10-15T18:00:00Z" } A verifier holding the sealed Output computes the SHA-256 digest of its COSE_Sign1 and compares it to sealedOutput.digest. A verifier that holds only this credential reads the Ledger entry for reconciliationHash before treating the verdict as more than a snapshot, and stops treating it as current at validUntil.

Composition with the SCITT Architecture The SCITT Architecture provides notarisation of supply-chain artefacts through a Transparency Service, which registers Signed Statements and returns Receipts, yielding Transparent Statements. ARP composes with SCITT in four ways:

1. SCITT receipts MAY be the input claim to ARP. A claim referencing a SCITT-anchored artefact (its hash and its registration receipt) is reconciled across registers without disclosing the underlying artefact.
2. ARP Reconciliation Outputs MAY be notarised into a SCITT Transparency Service as Transparent Statements, enabling SCITT-aware relying parties to verify the cross-sovereign reconciliation event in the same way they verify any other supply-chain claim. Registration and retrieval MAY use the SCITT Reference APIs . Notarisation does not enlarge the Audience Set of : what is registered is the sealed Output, and a party that retrieves it by EntryID holds it on the same terms as a party handed it directly.
3. The SCITT Architecture's Issuer role maps to the Bilateral Register Agreement structure: each Sovereign Register acts as a SCITT Issuer for a constrained predicate set. RFC 9943 defines no role for a party that combines statements from several Issuers, and this document does not claim one: the reconciliation server is an ARP role that acts as a SCITT Client toward the Transparency Service, registering its own Signed Statements.
4. ARP Hash-Linkage Aggregation MAY emit its Merkle commitment as COSE Receipts , a compatible inclusion-proof encoding SCITT uses for transparency receipts, so a single verifier library checks both.

Composition with the RATS Architecture The RATS Architecture provides remote-attestation procedures for compute-substrate trust. ARP composes with RATS in two ways:

1. The Adversarial Pre-Transmission Test runs inside a confidential computing boundary attested under RATS. The reconciliation server's integrity MAY be verified by relying parties through standard RATS verification flows.
2. Compute-attestation reconciliation across heterogeneous TEE / CC providers is the natural specialisation of ARP to the RATS evidence class. That specialisation is outside the scope of this document.

Composition with Agent-Action Accountability Capsules models accountable autonomous action as four independently verifiable slots -- CAN, what the agent was permitted to do; WHO, which human authorised it; WHAT the agent did; and AUDIT, the runtime enforcement record -- each filled by a separately signed profile. This document does not restate that model; the slot definitions, their semantics and their composition rules are those of , and this appendix uses them as defined there. This appendix calls a filled slot a capsule. That is this document's term and not that draft's, which speaks of slots and profiles; it is used here because ARP admits each filled slot as a Partial-Attestation source and the word names the signed unit rather than the position it occupies. What this appendix adds is reconciliation across those capsules. Each capsule may be signed by a different party, under a different signing chain, with a different payload schema -- the same non-reconcilable-outputs problem this document addresses for sovereign registers, arising in the agent-action domain. What the capsules share is the action serialisation over which the subject digest is computed. ARP composes such capsules without requiring them to share a producer, a schema, or a signing chain. The capsules are bound to a common action through a shared subject digest, computed as the SHA-256 of the JSON Canonicalization Scheme serialisation of the action being attested: subject_digest = SHA-256(JCS(action)) where JCS is the JSON Canonicalization Scheme specified in , and action is one action object serialised once. All capsules composed under this appendix MUST be computed over that same serialised action object. subject_digest is a join key across capsules over a shared serialisation; it is NOT a correlation key across independently produced descriptions of an act, and MUST NOT be used as one. See . The shared serialisation is established once, by the party that authorises the action, and is echoed verbatim by every later attester. An attester that re-serialises its own account of the action MUST NOT compute subject_digest over that account; it MUST carry the serialisation it received. This is what makes the digest a join key here rather than a correlation across independent descriptions, and a profile that cannot guarantee it is in the second case of rather than the first. Implementations MUST use and MUST NOT substitute another canonicalisation. In particular, does not apply Unicode normalisation. An implementation that normalises before serialising therefore computes a different subject digest from a conforming implementation for any input carrying a member name or string value that is not already in the normalisation form it applies -- silently, since both parties obtain a well-formed digest. The agreement of this construction with a deployed profile depends on both parties having selected , which the normative reference above makes an obligation. freezes a conformance vector only once two independent implementations have recomputed it and specifies no implementation, so no pinned corpus is cited here. The capsules may disagree about the action -- that disagreement is the finding ARP exists to surface -- but they do not disagree about which action is under attestation, because they carry the same action serialisation. Each capsule's own account travels in its payload, committed by its receipt-payload digest below, not in subject_digest. Two further profile-tagged digests, defined by this document rather than by , position each capsule for reconciliation: an authority-reference digest committing to the authorising instrument (tagged transparency where it is the Signing Input Digest of the COSE_Sign1 transparency receipt, an RFC 9942 receipt being signed by the Transparency Service and so within ; or offline where it is the SHA-256 of the serialisation of an offline receipt payload, which carries no signature), and a receipt-payload digest committing to the capsule's own payload. Each capsule is admitted to ARP as a Partial-Attestation source keyed on the shared subject digest, in the slot assigns it. The reconciliation server verifies each capsule's signature under its own trust anchor, projects each into the agent: predicate branch, and aggregates the per-capsule verdicts under the Verdict Arithmetic declared for the action class -- yielding a single, producer-agnostic Combined Verdict over an action whose constituent attestations were never designed to interoperate. Where the authorised-scope capsule and the actual-conduct capsule reconcile to divergent scopes, the Combined Verdict is no-match with divergence axis agent-action-scope-divergence; the divergence is a refusable control input, produced at decision time and sealed to the Settlement-Layer Ledger without claim or capsule content. This composition is the agent-action specialisation of the mechanism ARP applies to sovereign registers: reconcile heterogeneous authoritative outputs over a shared subject into one deterministic verdict, disclose only verdict and divergence, and seal against a Policy-Version Hash. It allows a relying party to reconcile what an agent was permitted to do against what it did, at the moment of action, across attestations no single party produced.

The digest constructions are distinct A third construction, the Signing Input Digest of , identifies a signed artefact by what was signed rather than by the envelope carrying it, and is over deterministic CBOR rather than over a JSON serialisation. It is distinct from both of the constructions below and from the Reconciliation Hash, which is over a Reconciliation Output with each embedded register signature replaced by its Signing Input Digest. Substituting any of these four for another produces a value that verifies against nothing. This document defines two digest constructions over a JSON serialisation, for two different purposes, and they are NOT interchangeable:

Claim Hash:

SHA-256 over the Canonical Claim serialisation of together with the Deployment Blinding Value of . Its purpose is to index a claim in the Settlement-Layer Ledger. It applies Unicode Normalization Form C.

subject_digest:

SHA-256 over the serialisation of an action, per . It is a CONTENT digest: it commits to the action object as serialised, and any difference in the serialised bytes yields a different digest except with negligible probability. does not normalise.

An implementation that substitutes one for the other MUST be assumed to produce incorrect correlations. The failure is silent: both constructions return a well-formed 32-octet digest for any input, so a substitution surfaces as a correlation that does not occur, or as two distinct actions correlating to one subject, rather than as an error. Two cases are worse than a mere difference of bytes, because the substitution produces a COLLISION rather than a mismatch. Under the Claim Hash construction, which normalises, an input in Normalization Form D and the same input in Normalization Form C yield the SAME digest; so do U+212B ANGSTROM SIGN and U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE. Under the subject_digest construction, which does not normalise, all four are distinct. An implementer who reuses the Claim Hash where a subject digest is required will therefore correlate two actions that a conforming implementation keeps apart. Neither case needs measuring: both follow from the two constructions as this document defines them, and either can be checked by computing the two digests over the four inputs named above. Accordingly:

• An implementation MUST NOT use the Claim Hash construction where subject_digest is specified, or the reverse.
• Where a digest is carried on the wire for correlation, the producer MUST identify the construction used, by an identifier that commits to the declared canonicalisation parameters -- member-sort code unit, normalisation, number rendering, absent-member handling and hash algorithm -- so that a consumer can determine compatibility rather than assume it. Such an identifier MUST NOT commit to facts about a specification that do not affect the serialised bytes, so that two implementations producing identical bytes share an identifier. expresses a compatible rule statement-side.
• Where the correlation digest is computed over a TYPED action object whose type declares required material fields, the producer MUST validate the object against a pinned definition of that type before emitting a correlation identifier for it, and MUST NOT emit one where validation fails. A digest is well-formed over any object, including one that omits fields the type requires; emitting an identifier in that case mints a join key for an action the identifier does not fully describe, which is the condition a relying party has no way to detect downstream. Validation against a pinned type definition is therefore required before emission.

What a content digest does and does not establish subject_digest is collision-resistant over content: two actions whose serialisations differ in any byte produce different digests except with negligible probability, so a receipt bound to one action does not bind another. That property is what makes it usable as a join key between capsules computed over the SAME serialised action. It does not, and cannot, establish that two INDEPENDENTLY DESCRIBED accounts of one act correlate. The action types, their required and optional members and the reference issuer that minted the instances measured below are those of ; the measurement is not reproducible without it. Where an action type declares optional members, two conforming producers describing the same act may legitimately differ on whether an optional member is present, and their subject digests then differ. Stability under permitted variation and collision resistance over content are contradictory requirements, and no single digest satisfies both. This is measured, not assumed. Five action objects, each a conforming instance of one registered action type and each accepted by that type's reference issuer, differing only in content the type declares OPTIONAL, produced five distinct subject digests. The divergence appeared at the first optional member and did not require any nested reference or unusual value. Accordingly:

• A profile MAY key capsules on subject_digest where those capsules are computed over the same serialised action object. is such a profile: the capsules it composes share one action serialisation.
• A profile that requires correlation across independently produced descriptions of one act MUST NOT rely on subject_digest alone. It MUST either pin the exact member set over which the digest is computed, so that permitted variation cannot enter it, or designate a typed field that the action type itself requires, and correlate on that. The second is the more robust of the two, because it does not require every producer to agree on a serialisation before they can agree that they are describing the same act. The selection is the profile's and not the registry's. declares required and optional fields per action type; it does not mark any field as a correlation key, and a specification that says an action type "declares a material identifier" attributes to that registry a semantic it does not carry. A profile therefore MUST pin the action type and its version, the field it has selected for correlation, and that field's normalisation and comparison rules. The selected field MUST be present in the Canonical Claim, so that the Claim Hash commits to it and the join cannot be made on a value the reconciliation does not cover. Equality of the selected value identifies candidate descriptions only. It MUST NOT establish action equivalence, authorisation or execution. Exact-action agreement remains a separate comparison, under the subject-digest construction of or under the profile of . Where the selected values match and the exact-action digests differ, that is a conflict to surface and not a failed join, and surfacing it is what reconciliation is for.

Three substitutions are forbidden, because each is available to an implementer who has read only part of the foregoing and each fails silently.

• The designated join key MUST NOT be treated as the action's identity. The identity of an exact action is its content commitment; the join key is stable across the variation that commitment is required to detect, which is what makes it usable for correlation and useless for authorisation.
• A Claim Hash MUST NOT be treated as a cross-deployment identifier. It is a digest over a canonical serialisation preceded by the Deployment Blinding Value of , so two deployments reconciling the same claim compute different Claim Hashes by construction, and equality of Claim Hashes across deployments is not a comparison that can be made at all.
• Equal join keys MUST NOT be taken to mean equal claims. Two reports sharing a designated join key have been asserted to describe one act; whether they agree about it is the question reconciliation exists to answer. Where their Claim Hashes differ, the difference is the finding, and a profile that collapsed them on the strength of the join key would report agreement it never established.

Stated positively, each object has one job: the designated field joins candidate reports across permitted variation, the Claim Hash commits to the exact claim under the deployment's blinding value, and the action type's own content commitment remains what authorisation and execution bind to. A specification that describes a content digest as a correlation key without stating which of the two preceding cases it relies on invites an implementer to assume a stability property the construction does not have. The resulting failure is a correlation that silently does not occur.

Document History RFC Editor: please remove this section before publication.

Since draft-hillier-scitt-arp-05

Mechanical

• The document is validated by both idnits and idnits3 with no error or warning other than those that follow from the Standards Track status itself: the downward references enumerated in the Note to the RFC Editor, and the normative reference to .
• Requirement-level keywords are marked with the bcp14 element, and the three sentences in which the verb "notarise" followed a keyword are reworded so that the keyword and the verb are not read as a single negated keyword.
• The obsolete Certificate Transparency reference RFC 6962 is no longer cited. is the reference, and states that the tree it defines is the tree earlier logs compute.
• The Web Bot Auth references are updated to , which defines the Signature-Agent header and the key directory it names. The separate directory reference is removed.

Since draft-hillier-scitt-arp-04

The Verifiable Credentials form is a complete profile specifies the credential form of a Reconciliation Output in full: its members, its securing as application/vc+cose under , the verification steps, and the mapping of the Reliance Horizon onto validUntil. A worked example and a 30-vector conformance class accompany it.

Four securing forms for one credential The credential is also specified in application/vc+jwt, in SD-JWT VC (application/dc+sd-jwt) with selective disclosure of the subject members and an optional key-binding JWT, and as an ISO/IEC 18013-5 mdoc IssuerSigned structure. The issuer's JWK Set resolves the Sealing key for every form. All four carry the same RFC 8785 payload under the same Sealing key, and a 30-row conformance class checks them independently.

Sealing-key discovery is exercised end to end A reconciliation server publishes its signed COSE Key Set, a single key by identifier, and a distinct operator key set. Each entry carries arp-key-status and arp-key-validity, retirement is by status, and the issuer JWKS names the same key under the same thumbprint kid. A 23-row conformance class decides resolution, status and validity, and the refusal of each malformed set.

Since draft-hillier-scitt-arp-03

The chain a head-consistency check is decided over The second branch of , where a witness Statement covers a head above the one a response names, now requires the chain between the two heads to be obtained from that witness's own origin, as the Witness Linkage Segments of , and forbids taking it from the responding service. -03 had the relying party read that chain from the service and anchor its two ends: the top to the Self-Entry Hash the witness signed, the bottom to the Self-Entry Hash the response named. Anchoring the ends of a service-supplied chain is not sufficient, and the reason is arithmetic rather than cryptographic. The condition anchors two Self-Entry Hashes and then walks a chain over two other positions, the Prior-Entry Hash and the Signing Input Digest. Neither anchored value sits in a position the chain reads. No value the chain does read can be recomputed by a party holding linkage arrays, a Signing Input Digest being taken over a Sig_structure and the array carrying no preimage. And the lower anchor is the response's own claim, so it constrains the responding service against itself. Every value the chain is made of is supplied by the party the chain exists to check, and an equality between two values one party supplies is not evidence about that party. This was established by executing the condition rather than by reading it. An independent construction of the Ledger chain and of the readers this document defines, written from the section text with nothing imported from any implementation, was run over a four-entry Ledger under six cases: served honestly; the digest moved whole; the digest moved with the witness observing before the move; one Reconciliation Hash changed at entry 2 with the chain re-linked and re-sealed and served plainly; the same rewrite with the witness-signed Self-Entry Hash served at the top of the span and the service's own values in every other position; and a response naming a head its own arrays do not carry. The condition as -03 stated it accepts the fifth. Replacing each of the nine hash positions of a three-array span in turn identifies three the condition never constrains, one of them an interior Self-Entry Hash, which is a value a relying party checking a receipt against a particular entry would otherwise take as attested. Two narrower repairs were constructed and neither reaches. Adding the Signing Input Digest of the covered entry to the Head Consistency Statement and checking the top array against it is defeated by copying one further value the witness already published, that position being one the chain does not read. Anchoring both ends in positions the chain does read pins the chain values of a three-array span, and only those: the interior Self-Entry Hash is constrained by neither anchor nor chain even there. From four arrays up the chain values between the ends are unconstrained as well. The span is the distance between a head a witness happened to observe and a head a response happens to name, which the relying party does not control, so a repair that holds only at three arrays holds only by accident. defines the artefact, its covering requirement, its Attestation Floor, its addressing and its equivocation rule; gathers the operational consequences; and register the media type and the well-known URI; records what unauthenticated publication of the arrays discloses. gains the entitlement and the ranged read a witness needs to produce a Segment at all, a Witness Entry key not being reached by the roles the other reads name. gains the artefact and restates the Witness Set and Witness Quorum entries, which described Statements alone as the evidence. The property is stated as what it is. A witness reads the Ledger from the reconciliation server, so what a Segment records is what that witness was served, under a signature it cannot revise and at a time it stamps. The assurance is therefore append-only: a conforming witness publishes each interval once and serves one Segment per entry, so an operator rewriting an interval a witness has covered can only do so with a witness that equivocates. Detection of that equivocation is opportunistic in the way already says detection of two entries at one Entry Sequence Number is, and says so rather than leaving the impression that a single verifier-side test catches it. An operator rewriting an interval no witness has yet covered is bounded by witness diversity and observation frequency and not by this mechanism, which is the residue already concedes for declared independence rather than a new one. The first branch of is unchanged: a Statement covering the named head exactly carries no span and needs no Segment.

One deterministic encoding, named by section now states that Section 4.2.1 of orders the pairs of a map in the bytewise lexicographic order of the deterministic encodings of the keys, that the Length-First Map Key Ordering of Section 4.2.3 is a different ordering which widely used libraries produce under an option named canonical, and that an implementation MUST produce the former, a library option named canonical not being evidence that it does. The two agree for any map whose keys are integers or strings and share a CBOR major type, at any mix of lengths: for those types the head byte never decreases as the encoding lengthens, and where two keys share a head byte the bytewise comparison runs on into the bytes after it and orders them the same way. Those are the keys COSE admits. That is why the difference travels, and why a protected header carrying COSE labels 1 and 4 is unaffected. They diverge only where a map mixes major types and the key of the higher major type has the strictly shorter encoding: a label of -1 is the single byte 0x20 and a label of 256 is 0x19 and two further bytes. No protected header this document specifies reaches that case, and the requirement is stated so that none added later does, since permits private-use labels pending registration and private-use labels are negative. Where the case is reached, one protected header has two encodings, one signing act has two Signing Input Digests, the entry above has two Prior-Entry Hashes, and treats that as a fork. This is the Collection order class of reaching a place that section did not name. Its bullet covered the permutations of a set and is extended here to the orderings of the pairs of a map, which is the one member of the class where the freedom is exercised by a library default rather than by an implementer's choice: an implementation that reads the requirement correctly and reaches for the obvious option still departs from it. The eight classes are unchanged in number.

A floor on the response freshness tolerance Item 26 of and now floor the declared tolerance at sixty seconds as well as capping it. The bound runs backward from the reader's receipt of the response and the response was produced before that instant, so a tolerance below the transit and clock disagreement between the two parties rejects every honest response, and a tolerance of zero rejects all of them. That is an outage a deployment could declare itself into with no party misbehaving and no conformance test firing, which places it with the Witness Set constraint of rather than with the parameters a deployment tunes. Sixty seconds is the figure already fixed for the forward bound of this test and of the two others that bound a party against another's clock over a message it has just received, so the narrowest admissible interval is symmetric. Those three differ in their backward bounds and agree in their forward ones. A fourth, the witness observation window of , runs over an artefact published on an interval rather than over a message, and this revision floors it at sixty seconds in both directions while leaving the interval free to widen the forward bound: unfloored, a deployment notarising every few seconds admitted a window of a few seconds against an unsynchronised clock. states all four rather than leaving them to be collected. Where a deployment's effective notarisation interval is shorter than sixty seconds the floor governs, a ceiling below a floor being a term no deployment can declare, and that deployment trades the supersession property for liveness by exactly the difference between the two figures. The trade is stated rather than left in the arithmetic, and a deployment wanting both notarises no more often than sixty seconds.

Certificate Transparency, and the leaf a proof carries now states its relationship to Certificate Transparency, which -03 named only in its Acknowledgments while defining a Merkle construction in its body. An implementer arriving from Certificate Transparency had no way to tell from the text whether the two constructions agree. The finding is Tom Sato's. The relationship was established by executing both constructions rather than by comparing their prose. The odd-node rule of and the recursive split at the largest power of two below the leaf count of Section 2.1.1 produce identical roots for every leaf count from 1 to 4200, and identical sibling arrays for all 131,328 leaf-count-and-index pairs up to 512 leaves. They diverge at one input in that whole range: the empty tree, where this document gives thirty-two zero octets and Certificate Transparency gives the hash of the empty string. That divergence is kept, and the section now says why -- the Certificate Transparency value is a digest a verifier reproduces successfully and may then treat as a root that commits to something, and thirty-two zero octets is a value no commitment in this document produces. The section also states what an implementation ported from a Certificate Transparency log gets wrong if it is carried over unchanged: this document sorts and deduplicates leaves where a log commits to submission order, and this document's inclusion proof carries the leaf where the inclusion proof of Section 2.1.3 does not, carrying the index and the tree size as this document does but assuming the verifier already holds the leaf. And it records that the third convention in common use -- duplicating the last node at an odd level -- agrees with this construction at every leaf count that is a power of two and disagrees at every other, so a conformance vector taken at four or eight leaves will not detect an implementation that ported it. is new and is the security-relevant part. -03 defined the inclusion proof as carrying the leaf and said nothing about where a verifier should get the leaf it checks against. A proof whose carried leaf is lifted unchanged from another object's valid proof folds to the correct root under a sibling array that verifies, because it is a correct proof of the other object; a verifier that walks the path first and trusts the carried leaf accepts it and concludes that the object it holds was committed. Nothing in the walk depends on the object, so no amount of path checking detects it. A verifier MUST now compute the leaf from the object whose inclusion is being proved and use that value, and no value taken from the proof, as the input to the walk. The requirement is stated over the object rather than over the carried field because permits COSE Receipts , whose inclusion proof carries no leaf, and a rule written only as a comparison against a carried leaf would be vacuous under exactly the encoding a SCITT-aware verifier is most likely to use. The finding is Nenad Vasic's, contributed as an executable vector against a third-party corpus. Two errors in the -03 text of are corrected. The sibling-derivation rule said the verifier halves "the index and the level width" as it ascends; the level width halves by ceiling, not by truncation, and an implementation following the sentence literally computes the wrong width at every leaf count that is not a power of two -- which is the entire range the paragraph exists to pin down. And described COSE Receipts as "the same inclusion-proof format", which they are not: an RFC 9942 inclusion proof carries no leaf and is defined over the RFC 9162 tree whose empty root this document rejects. also loses a stray duplicated clause.

Every digest that identifies a signed artefact is new, and five constructions changed with it. -03 took the Prior-Entry Hash of over the whole preceding entry including its Entry Signature, the Post-Seal Evaluation Record Hash of over its record "in its entirety, signature included", the Merkle leaf of over a canonical hash of a register-signed Partial Attestation, and the tagged-transparency authority-reference digest of over a COSE_Sign1 receipt. Those four are now Signing Input Digests. The Reconciliation Hash of is the fifth and took a different repair, below. The reason is a measurement. For ECDSA, (r, s) and (r, n - s) both verify against the same key over the same message, and no specification prohibits it: Section 4.1.4 of SEC1 v2.0 and Section 6.4.2 of FIPS 186-5 range-check r and s only, and Section 2.1 of constrains neither. Nothing is forged and no authority is bypassed -- a party holding no key produces the second encoding from the first, in transit. Over two hundred random P-256 keys, two hundred substitutions verified and two hundred changed the entry bytes. The finding is Anton Sokolov's. The Reconciliation Hash is where the repair nearly failed. -03 defined it as excluding the Sealing Signature, and an earlier draft of this section asserted on that basis that it was already outside the signature and unchanged. It was not. embeds a register signature in each Query Binding Record and in each Non-Answer Statement, so the preimage still carried a signature after the sealing one was removed -- measured, stable in none of two hundred trials. The Reconciliation Hash is a field of every Settlement-Layer Ledger entry, hence inside the Entry Signature payload, hence inside the Prior-Entry Hash: leaving it would have reintroduced at one remove exactly what fixing the Prior-Entry Hash removed. It now replaces each embedded register signature with that signature's Signing Input Digest. That is the second instance in two days of this document carrying the sound rule and the unsound one at once. The first was in a single bulleted list, where the Self-Entry Hash nulled the signature position and the Prior-Entry Hash two paragraphs below it did not. The instruction to sweep every identity rule in a document rather than correct the one that was reported is Henri Sirkkavaara's, from finding the same split in his own implementation on the same day, and the Reconciliation Hash is what the second sweep found. Two things earlier revisions detected are no longer detectable, and now says so rather than leaving it to be discovered. Stripping a historical Entry Signature while leaving its protected header and payload intact moves no Prior-Entry Hash, and neither does re-signing an entry under the same key and header. A re-signature under a different key or algorithm still moves the chain, because the Sig_structure covers the protected header. The "signed exactly once" rule consequently has no verifier-side test and is stated as an operator obligation an Audit Identity can examine. now requires every COSE_Sign1 this document defines to carry the algorithm and key identifiers in its protected header and not in an unprotected one. Nothing previously required it, while both 's definition and 's rotation argument assumed it -- and RFC 9052 permits alg in the unprotected bucket, which a Sig_structure does not cover. also fixes the external additional authenticated data at the zero-length byte string, because a Signing Input Digest a third party cannot reproduce is not an identifier. is rewritten where it rested on this. Its conclusion survives and both its reason and its stated cost change. The chain holds because the Prior-Entry Hash is over the signing input; and a verifier recomputing one takes the protected header and payload byte strings verbatim and MUST NOT re-encode them, which is more than -03 asked rather than less. -03 required copying bytes and hashing them; -04 requires parsing a COSE_Sign1. That is the price of a digest that does not move when the signature encoding does, and an earlier draft of this section had the comparison backwards. The consequence of the old constructions was a failure of verification rather than of authenticity, which is the harder kind to diagnose. A reader served a substituted entry concludes the chain is broken when the operator equivocated about nothing; under it refuses a valid inclusion proof. A deployment reporting either as detected tampering reports something that did not happen. is added as an informative reference for Section 8.4 alone: EdDSA puts the low-S check inside verification, so an attacker cannot derive a second verifying byte-string, and a deployment declaring only EdDSA primitives under item 2 of is not reachable by this. That is non-malleability and not a claim that one byte-string alone can ever verify, since Section 5.1.7 of leaves cofactored verification optional. Nothing in this document requires EdDSA, which is why the constructions and not the primitive choice are where this is addressed.

The Bilateral Register Agreement is new. The Bilateral Register Agreement is what makes a register addressable, and -03 defined it in a definition-list entry in : one paragraph enumerating twenty-six declared items and the Agreement Hash construction over them. That is normative content with MUST-level force, sited where a reader looks for a definition and not for a requirement, and unreadable at the length it had reached. It is now a section, the enumeration is numbered, and the numbering is what fixes the Agreement Hash order. Gathering it surfaced two obligations this document places on an Agreement elsewhere and never enumerated here, so that neither was covered by the Agreement Hash. obliges a deployment to declare a response freshness tolerance; that is now item 26. obliges an Agreement to declare the keys under which a regulator reads, and the regulator-identity-provider trust anchor of item 5 is not a key; that is now item 30. In both cases two deployments could agree on every item the Agreement Hash committed to, differ on the term, and compute the same Agreement Hash -- an Agreement Hash that does not cover a term the Agreement is required to carry, which is the class of defect this document exists to prevent. Item 31 makes the re-invocation permission already conditions on a declared term for the same reason. now fixes the CBOR type of every item and requires every set-valued item to be sorted in bytewise lexicographic order of the deterministic CBOR encoding of each element. Determinism under Section 4.2.1 of fixes how a given value is encoded and does not fix which type an item takes or how a set is ordered, so -03's construction was not one two parties could independently compute even with the item order settled. It also states that the array has exactly thirty-three elements and that an absent, inapplicable or empty item is encoded as CBOR null with the element still present, naming the four items that may be absent -- -03 said only that an absent optional item was null, while more than the one OPTIONAL item admits absence. Since suspends reconciliation on a deviating Agreement Hash, each of these was an outage rather than a warning.

The witness quorum specifies the witness quorum. -03 stated, in , that a relying party acting on an empty result SHOULD hold head-consistency evidence from at least one observer independent of the responding service, and said in terms that it specified no quorum. The condition was therefore normative while the thing that satisfies it was not. The finding that this is bounded by observer diversity rather than by any stronger single-log property is Walter Hawkins's, carried from -03. What satisfies the condition in its multi-entry form is stated in the entry above rather than here: this entry records the quorum, and the chain a quorum is evaluated over comes from the witness under . An Agreement now declares a Witness Set and a Witness Quorum, both of which enter the Agreement Hash. gives a Witness Entry a form and an Operating-Party Identifier with a stated normalisation, so that "distinct" is a test a verifier computes rather than one it decides. The exclusion runs in every direction -- a witness may not be operated by the responding service, by a party controlling it, by a party it controls, or by a party under common control -- because an exclusion running upward alone excludes nothing that matters: a server that incorporates three subsidiaries satisfies a quorum of three while controlling every observation in it. gives the Statement a payload, a media type and a registered protected-header parameter, and carries a Witness Observation Time, because a COSE_Sign1 is not dateable from its own bytes and a freshness rule over an undateable artefact is a rule no verifier can apply. requires that a Statement covering a higher head be accompanied by the chain linking that head back to the one the response names, verified by Prior-Entry Hash. A witness signature over a higher head is otherwise evidence about whichever branch that witness was served, and a fork at disjoint sequence numbers is precisely a pair of heads neither of which contradicts the other; only the linkage puts the two observations on one chain. Where that chain is obtained is settled by the entry above, which replaced a chain read from the responding service with the Witness Linkage Segments of : the requirement to link stands, the source of the links does not. It also measures the freshness window from the Statement Timestamp of the Ledger Head Statement rather than from the head's own Entry Timestamp, and sets it at two notarisation intervals, because republishes once per interval and a one-interval window measured from an entry's own timestamp closes before any witness can see that entry. That window is floored at sixty seconds in both directions, for the reason the entry on the response freshness tolerance gives: a window narrower than the disagreement between two unsynchronised clocks fails an honest party permanently. puts the effective Witness Set and Quorum in the Policy Parameters Document of . A relying party is party to no Agreement and holds only Agreement Hashes, so a quorum declared solely inside an Agreement is a test the party obliged to run it cannot read. states what none of this establishes. Operating-Party Identifiers are declared and not proven; the exclusion is normative and the detection of a false declaration is not provided for. A met quorum is proof that observer diversity was declared, by a named party, in a term that party can be held to.

The head-linkage projection gains a fields=linkage projection returning the Entry Sequence Number, Prior-Entry Hash, Self-Entry Hash and the Signing Input Digest of the Entry Signature of one entry, entitled to any requester whose signature verifies. The projection was specified so that a relying party could link two heads itself; the entry above supersedes that use, and the projection's reader is now the witness, which needs the same four values to publish the Segments of and reads them for a range. The fourth element was added after the projection was specified with three: the chain condition of compares a Prior-Entry Hash against the Signing Input Digest of the entry below, that digest is taken over a Sig_structure, and neither the protected header nor the payload of the entry below is recoverable from a triple of one sequence number and two hashes. The condition was uncomputable by the party then required to compute it, and the substitution a reader might have reached for instead is the one the same section forbids. The fourth element is what a witness now commits to, so the repair holds under the entry above rather than being superseded by it. The projection is bounded at the head of the most recently published Ledger Head Statement. Unbounded it would be a live head oracle -- the Ledger is contiguous, so a requester could binary-search the current head between publications and poll it for the write rate, which is the disclosure publishes the head only once per notarisation interval to prevent. states why a projection answering 200 where the full read answers 404 is not an existence oracle, and what would make it one. No timing claim is added by this revision and none is tested. continues to state that response timing is a separate claim which an implementation must either make with its measurement conditions published or not make at all, and that making none is not non-conformance.

Six adversarial passes, and what they found The changes above were made in response to review. The changes below were made in response to a sweep run against this document with the specific intent of breaking it, from six directions at once, before anyone else did. They are grouped by what they say about the document rather than by section, because the grouping is the finding. Three sentences claiming rigour were the least rigorous sentences in the document. said the falsifiability argument holds for three triggers in four, "stated rather than rounded up". It held for one. Two of the three rested on a transition array published by the reconciliation server, under its own key, in a Policy Parameters Document with no publication time, no notarisation and no chain, so a transition omitted from the array started no clock and no party could date the Document well enough to show that it had been. now gives that Document a Publication Timestamp, requires it to be notarised on the ledger-head interval, and requires republication on that interval whether or not its contents changed. The claim is now three in four and is stated as conditional on that anchoring. said "every digest in this document that identifies or chains a signed artefact" and enumerated five. There were seven. The Override Record of carries a COSE_Sign1 by the authorising operator inside the Reconciliation Hash preimage, and the Evidentiary Provenance Manifest of could carry one inside the Claim Hash preimage. The rule is now stated over the class -- in any preimage this document defines, every signature made by a party other than the one computing the digest is replaced by its Signing Input Digest -- because an enumeration of carriers is correct only until someone adds a field. The Manifest could not be repaired that way, its preimage being JSON with no byte-string type and its octets being the requester's, so signed artefacts are now prohibited inside it and carried beside it by digest. said two instances of one observer are not two observers and tested distinctness on the Operating-Party Identifier alone. Two entries declaring one key under two identifiers satisfied a quorum of two with a single signature. now requires pairwise distinct Verification Method References, which is a mechanical test, and states why that is different from the declared-independence limit concedes and cannot close. Two paths reached a decisive verdict out of nothing. An empty Addressed-Registers Identifier Set yielded match under conjunction: every operator in is a condition universally quantified over the contributions, and both precedence rules began "where any", so at zero contributions every guard was vacuously satisfied. A source class containing no addressed register yielded a decisive no-match, which conjunction propagated. Neither required an operator to misbehave. Both are now closed by explicit rules. Nothing bound the subject. The transformation from the Canonical Claim's Subject Identifier to the Subject Reference each register was asked about was unrecorded, unconstrained and invisible to every party outside the reconciliation server. Every signature could verify, every binding recompute, the chain hold and the notarisation pass, while every register answered honestly about a different person. adds a Subject Mapping Record carrying the Subject Reference and a registered descriptor naming a transformation that must be a function of the Subject Identifier and declared terms alone. Evidence about a party was obtainable only from that party. Head Consistency Statements had an artefact, a quorum rule, a linkage chain and a freshness window, and no channel. The obvious implementation has the responding service supply them, which satisfies every stated condition and defeats the mechanism entirely under exactly the fork it exists to detect. Witnesses now publish on their own origins and a relying party MUST NOT accept one from the responding service. Vocabulary that did not reach the output. A verifier told to refuse a proof had no way to record which of four refusals it made; adds them, and requires same-act-distinct-encodings to be tested before any outcome that accuses a party of equivocation. One Non-Answer Reason carried five distinct causes because four other sections directed implementations to it for conditions its own definition never named; it is now five reasons. Claims a mechanism could not support. The Reconstruction Proof of had no pinned preimage, no wire representation, and compares one value the audited server produced against another value the same server produced under a key only it holds. The preimage and the wire form are now fixed, and the stated limit is corrected: equality establishes self-consistency across two reads and nothing else. The Examined-Set Root's counts were said not to be bare assertions, which already contradicted; they are assertions, made attributable and dated by the signature and the notarisation and not made verifiable. The Regulator Portal audit trail was called subpoena-grade with no sequence, chain, head or notarisation behind it, and is now given all four. Things two implementers would encode differently. A CBOR type table for the Reconciliation Output; deterministic encoding stated for the Self-Entry Hash preimage; authority origin defined as an Authority Origin against ; element types for the Query Binding preimage; a form for the Audience Member Identifier; one canonical form for a key identifier and its two conversions; an ordering rule, a form discriminator and an equality rule for the Source-Data Version Identifier Set; an equality relation for the Witness Set intersection; a member form for the fifth Divergence Axis; a subject key for the query budget; a reference instant and direction for the freshness window; and the edges of the Predicate Taxonomy the projection function walks. Things no implementer could satisfy. The reproducibility requirement of was stated as identity in every field save an enumerated carve-out, and three fields that are necessarily fresh were not in it. The fields=linkage projection returned three values where the chain condition it exists to serve needs four. The response freshness tolerance every reader must apply was readable only by the parties who do not have to apply it. Suspension under had no defined exit. Privacy. takes the threats of in turn and states the residual rather than the mitigation where there is one, including exclusion, which this protocol does not mitigate. states the one property that makes erasure implementable against an append-only record -- no personal data enters the Ledger, and no chain depends on the continued existence of content that could be erased -- and prohibits notarising an Output where that disclosure has not been accounted for. What was looked for and not found. Several candidates did not survive verification and no change was made for them: the Claim Hash's unverifiability outside the deployment is already stated in two places; notarisation-incomplete already distinguishes pending, refused and never-attempted; the register key discovery root already has an encoding, a media type and a trust anchor; and the containment requirement of is satisfiable, though its named enforcement measure could not reach six fields the reconciliation server is obliged to read, which is now stated.

Five mechanisms taken from outside this field The repairs above answer review. These five answer questions the document could not previously answer at all, and each is a technique this field has not used and another has. -- every encoding defect is one defect. A signature with two byte forms, a CBOR item whose type is unfixed, a set with no order, an optional member omitted or nulled, a URI normalised or not, NFC or NFD, base64 or hex, transmitted bytes or a re-encoding. In each the information is the same and the representation differs, and the digest was defined over the representation. Physics has a name for a quantity that must not depend on a choice carrying no information, and the discipline that goes with it is to identify the freedom and quotient it out rather than to patch each place it shows. The section names the eight representation classes this document recognises, requires every new digest to state which class each preimage element belongs to, and requires a conformance runner to exercise the class rather than an enumeration of previously observed defects. A runner testing the two ECDSA encodings it has heard of confirms what its author knew; a runner enumerating the class finds the member nobody thought of. -- an estimator where there is no proof. The sweep identity below closes the gap between the counts and the Ledger. Nothing closes the gap between the Ledger and the world, because an operator that never wrote an entry has nothing to be caught balancing, and that is the omission problem in its general form. It has no proof and it has an estimator. An Audit Identity publishes a commitment to a set of Claim Hashes it intends to commission, then commissions them as ordinary reconciliations the server cannot distinguish, then requests the inclusion proofs already obliges the server to return. The recovery fraction estimates the proportion of eligible Outputs the sweep actually examined, and the shortfall estimates the population that was never written down. Astronomy injects sources of known brightness into an image to measure what its pipeline missed; ecology releases marked individuals to bound a population it cannot count. Both are estimating the same thing: what an instrument failed to record, from a known signal passed through the same instrument. A retroactive sweep is an instrument of that kind. The commitment precedes the probes so that the denominator is fixed before the numerator is knowable, which is what makes the fraction evidence rather than a selection. The sweep identity in -- accounting rather than signature. The examined count and the materially-changed count were assertions of the signing server. They are now required to balance against the Ledger: the Examined-Range Set must be contiguous over the interval it claims, the examined count must equal the number of reconciliation entries in it, and the materially-changed count must equal the number of continuation-supersession entries appended over the same interval. A signature makes an assertion attributable; an identity makes it checkable against something the asserting party does not solely control, which is what double-entry bookkeeping has done for six centuries and what a conservation law does in physics. The Examined-Range Set -- coverage needs a dense space. A Merkle root over Claim Hashes proves membership and cannot prove coverage, because Claim Hashes are sparse in the digest space and a set commitment has no notion of what is missing from it. Entry Sequence Numbers are dense and contiguous, so a gap in them is visible. Committing to the same sweep in both spaces lets one artefact answer both questions, and the choice of space is the whole of the trick. -- locating the loss. Several properties this document wants cannot hold together, and a specification facing that can claim both and be wrong somewhere a reader must find, weaken both and deliver neither, or choose and say where the loss went. The section is the third, in one table. What makes it useful is that the loss is located rather than distributed: a reader who knows which property was surrendered and where can compensate, and a reader told that everything holds cannot. Two rows that stood in earlier revisions have already been retired by the mechanisms above, which is the other thing the table turns out to be -- a list of what to attack next.

The two clocks a response freshness check is decided across now bounds the two clocks a response freshness check is decided across. -03 required only that response-time fall within a declared tolerance, naming no reference instant, no direction and no forward bound, so a response-time stamped ahead of the reader's clock was inside the tolerance on one reading and outside it on another, and a server whose clock ran fast was indistinguishable from one stamping ahead deliberately. The reference instant is now the reader's receipt of the response, the direction is backward, and the forward bound is sixty seconds. That figure is not new to this document: it is what already allowed on the Freshness Timestamp and what already allowed on created, both of which protect the server against the reader's clock. The reader was the one party to the exchange the same bound had not been applied to. Item 26 of now states that the declared tolerance is the backward bound only and that the forward bound is not negotiable per Agreement. The question is Emek Can Dogru's. The repair invents no mechanism. It applies, in the return direction, a bound this document had already chosen twice in the other one.

Mechanical Anchors were added to sections that had none -- , , and -- so that can cite them. No heading text changed. Item 2 of cites for the post-quantum primitives a deployment has selected. is added as an informative reference: it is the current Certificate Transparency specification. It is not normative, because the construction is fully specified here, so no downref is introduced. Four counts are corrected. described two of five items as already relied on elsewhere in this document where three of seven are, and said the Agreement Hash covers five items it did not cover before where it covers seven, items 32 and 33 having been added after that sentence was written. The mechanisms taken from outside this field are five, under a heading that says so and an opening sentence that said four. requested twelve media types while listing thirteen, and now requests fourteen. Separately and not as a correction, requests eight well-known URIs where it requested seven, the eighth being the one a Witness Linkage Segment is served at.

Since draft-hillier-scitt-arp-02 This revision answers a review of -02 on the SCITT list. Of its five asks, three are adopted as put, one is adopted in its goal and not in its mechanism, and one is declined for now with a reason. now names the evidence that bounds the empty-result falsifiability condition. -02, and this revision as circulated for comment, said that an empty result is falsifiable to the extent that the reader "independently holds head-consistency evidence" for the served chain, without saying independent of whom. Head evidence obtained from the responding service bounds nothing, because a fork at disjoint sequence numbers is invisible from a single vantage by construction and the vantage is what is in question. The condition now names an observer independent of the responding service and carries a SHOULD on the relying party, with witness countersignature over the head preferred to an independently anchored head digest. The gap is not closed and is not claimed to be; it is bounded by evidence an implementation can be said to hold or not hold. The finding is Walter Hawkins's. is new and normative. -02 composed with the SCITT Reference APIs permissively -- Reconciliation Outputs MAY be notarised, registration MAY use the APIs -- which is a permission and not a binding: two implementations could both conform to -02 and fail to interoperate against the same Transparency Service. The section now fixes the registration endpoint, the COSE_Sign1 framing and content type, receipt validation, and the asynchronous registration path. The asynchronous case is stated as a requirement because it is the most likely divergence between conforming implementations: a 202 Accepted with polling against 204 No Content is not the same code path as a 201 Created, and an implementer who codes only the latter interoperates with some Transparency Services and not others. The review also asked for a standard retrieval path keyed on the Policy-Version Hash. That is not specified here, because defines retrieval by EntryID and defines no query surface at all; a binding that specified one would specify an endpoint that does not exist. The goal -- preventing policy equivocation over time -- is met instead by requiring the Policy-Version Hash in the protected header of the Signed Statement, so that it is covered by the Receipt. A relying party therefore establishes the policy version by verification rather than by lookup, which is the stronger property: an index can be wrong, or can present different results to different relying parties, and a signed protected header cannot. is new. -02 specified the controlled projection function over an abstract Predicate Taxonomy without saying how an implementer determines what a given register can answer. Four profiles are defined -- , with , with , and consolidated sanctions list formats. Profiles constrain predicate expression only and are prohibited from introducing any means of transporting register records, which would defeat the property the protocol exists to provide. is new, and is the substantive addition rather than the largest one. A designation verdict against a consolidated sanctions list is meaningful only relative to the state of that list, and consolidated lists are republished on a cadence and distributed as deltas. -02 could therefore record that a historical Combined Verdict had changed but could not attribute the change: a verdict that flipped because the policy changed and one that flipped because the list changed were indistinguishable, and Sovereign Re-Notification reported both as policy changes. Partial Attestations now carry a Source-Data Version Identifier under signature, Retroactive Evaluation must distinguish the two causes, and where it cannot it must report attribution-indeterminate rather than attribute the change to policy. A list-state identifier is a property of a published corpus and not a register record, so this does not weaken minimum disclosure. Three structural gaps predating this revision are closed, because the new material could not be made testable without them. enumerates the Reconciliation Output, which no earlier revision did although both the Partial Attestation and the Ledger entry were enumerated; Reconciliation Hash and Combined Verdict are now defined in , the former having been used inside the bit-for-bit determinism requirement while undefined; and the Server-Recorded Divergence-Axis Set is a set, since a reconciliation may be qualified on more than one axis and a single-valued encoding would force a silent choice. is new. Where a narrowing means a register's answer does not bear on the claim as asked, that register's contribution is re-typed before aggregation rather than the Combined Verdict being overridden after it, so the Verdict Arithmetic resolved under is never displaced. A match found at any depth still establishes an existential closure predicate and is not re-typed. is new. Notarisation outcomes and retroactive attribution failures arise after a Reconciliation Output is sealed and so can be carried neither in a Partial Attestation nor in the Output; they are Post-Seal Evaluation Qualifiers recorded in a separate signed record referencing the Reconciliation Hash, and are expressly not Divergence Axes. New Divergence Axis values: register-threshold-divergence, declared-not-determined and source-version-skew. New COSE header parameter arp-source-data-version, carrying a set so that a register consulting several lists can denote the state of each. arp-bilateral-agreement-hash now always carries a sorted array, of one member on a Partial Attestation and one per addressed register on a Sealing Signature, so that a decoder never has to infer the type from context. New IANA registries for Register Data-Format Profile identifiers and for Post-Seal Evaluation Qualifiers. -03 adds registries for Ledger Entry Types, Override Grounds, Retroactive Evaluation Triggers and Aggregation-Method Descriptors. moves from informative to normative, because imposes requirements that cannot be met without it. A role-by-role walkthrough of the whole pipeline -- requester, agent, reconciliation server, register operator, relying party, Transparency Service, regulator, retroactive subsystem and IANA expert -- was run against this revision and found a further class of defect that no earlier review had reached: requirements addressed to an actor that does not hold the inputs they name. Those are closed here, and most of them predate -02. now enumerates the Per-Register Claim Projection. It is the only structure a sovereign register receives and it was the sole major structure in the protocol without a field list, which made the register role unimplementable. The register echoes the Policy-Version Hash rather than computing it, and the server MUST now send one Policy-Version Hash to every addressed register and verify each echo -- without which the per-register signatures over it, the only independent corroboration the protocol has, were discarded at aggregation. is new. -02 and the earlier -03 text told a relying party to verify a Sealing Signature whose key it had no way to obtain: it holds hashes of bilateral agreements it is not party to. Sealing keys are now published at a well-known location on a declared authority origin, mirroring how treats Transparency Service keys. is new. Every operator is now given its result for every combination of contribution values, and whether it admits partial-match, on which turns. -02 delegated combination to an operator it named but never defined, so two conforming implementations could produce different Combined Verdicts from identical inputs while the determinism requirement demanded they not. is new. A register may fail to answer in eleven distinct ways and no earlier revision defined an outcome for any of them; dropping the register silently produces exactly the addressed-register-cherry-picking the adversarial test exists to detect. A reconciliation with any non-answering register can no longer reach a decisive Combined Verdict. The Reconciliation Output gains the Claim Hash, a timestamp, the Verdict Arithmetic, the Sealing-Key Identifier, per-register attested and effective verdicts with the re-typing ground, per-register echoed Policy-Version Hashes, and register attribution on the server-recorded divergence axes. Without the Claim Hash a relying party received a verdict with nothing to attribute it to, and the retroactive subsystem had no key to select on although the Claim Hash was already declared its key. The Settlement-Layer Ledger gains the Claim Hash and now exposes READ as well as APPEND -- the Regulator Portal, retroactive evaluation and the chain-invariant check all require reads that "only APPEND" forbade. Ledger entries are now signed, because prior-entry hashes prove that nothing was removed from a chain and not that only one chain exists. The Ledger now carries two kinds of entry under an Entry Type discriminator, and each type's fields are enumerated. Facts arising after an Output is sealed -- the outcome of notarisation, a Post-Seal Evaluation Record, a supersession -- are recorded as Continuation entries appended against the Reconciliation Hash they concern. An earlier revision of this text described Continuation entries without giving them a form: they carried fields the entry list did not admit, supplied none of the fields it made mandatory, and nothing distinguished one kind from another. correspondingly no longer requires a Post-Seal Evaluation Record Hash to be appended to an already-signed entry, which the Ledger's absent UPDATE made impossible. Supersession is now recorded from both ends, the superseding entry naming what it replaced and a Continuation entry naming what replaced it, because neither pointer is reachable from the other's starting point. A retriever of a Post-Seal Evaluation Record must now check the retrieved bytes against the hash carried beside them, and that hash's construction is defined. A supersession entry carries the superseding entry's sequence number rather than a retrieval URI: obliging every reader to dereference an operator-chosen URI before it could check anything would have been a forced fetch, a de-blinding oracle and a covert channel no constraint on the URI's content could close. The Self-Entry Hash is defined, and is taken after the type-specific fields so that it covers them. The Prior-Entry Hash is now taken over the whole preceding entry including its Entry Signature. Chaining Self-Entry Hash to Self-Entry Hash would have left every signature outside the structure that detects tampering, which is a poor place for the field this document relies on to make a second chain attributable. Entry encoding and field order are stated, because the Self-Entry Hash is taken over them and a CBOR map would have been re-sorted by key.

Five things the protocol assumed and never stated Working through the Ledger changes made it clear that a class of gap ran under all of them. Every discovery path in -02 ended at a value its holder could not present to anything, and each attempt to fix one by adding a pointer moved the dead end without removing it. Five substrate layers were missing. They are now written, and adding them closed more open items than any mechanism in this revision. states what the pipeline returns. No earlier revision said that a Reconciliation Output is delivered to anybody. The document specified in detail how an Output is composed, sealed, digested, ledgered and notarised, and never that any party receives one. Every discovery path begins with a party holding a Reconciliation Hash; until now nothing said how it came to hold one. states who may hold an Output. -02 made it a bearer artefact: possession was the whole of the entitlement, it never expired, and every read predicate the document attempted was expressed in terms of a Requester-Binding the reader could not present and the Ledger could not evaluate. An Output now carries a sealed Audience Set and a Reliance Horizon. Entitlement follows the Audience Set rather than possession, which admits the party the Requesting Principal named and excludes the party that merely came into possession; a register may cap how wide an Audience Set addressing it may be, because a register that attests about a subject is entitled to bound how far that attestation travels. The Horizon bounds reliance without touching validity: a sanctions no-match is a statement about lists that change daily, and an artefact asserting one indefinitely was relied upon indefinitely. states how a read is requested. -02 and every draft of this revision before it stated what a read returns and never the endpoint, the request form, the response form, the media type, or the error semantics -- and the two errors that matter most, "nothing exists" and "you may not ask", are the two a reader most needs distinguished, because a server suppressing a supersession returns what a server with nothing to report returns. There are nine operations. Every response, success or error, is signed and carries the ledger head it was served against, so an empty result is an assertion rather than an absence, and a supersession later found at an earlier sequence number is evidence against the operator who signed the denial. Not-entitled and not-found are both 404 with no distinguishing body, so no endpoint is an existence oracle. Reads are rate-limited, because a surface whose every individual answer is innocuous discloses entry count, write rate and retroactive-burst timing when swept. With those in place, the Continuation entries of this revision are reachable by the parties they were written for, a superseded Output's replacement is retrievable because a superseding Output inherits the Audience Set of what it supersedes, and the fork check reconciles two heads at different sequence numbers through a signed consistency read rather than through an unsigned answer from the party under suspicion. Retrieval URIs, which an earlier draft of this revision put in Continuation entries, are gone: every artefact is now fetched by hash from the origin that served the entry, so the Ledger holds no retrieval address, no reader is obliged to dereference an operator-chosen URL before it can check anything, and the covert channel that host selection and path structure carried is closed. The published ledger head is a signed statement carrying a sequence number, and Entry Sequence Numbers are allocated in one sequence so that two conforming stores cannot present the same number over different entries. Two limits are stated rather than claimed away: an operator publishing to two audiences at disjoint sequence numbers never emits a colliding pair, and a party holding neither an Output nor an agreement cannot anchor the signing key. The Reconciliation Hash is no longer among the values required to be reproducible across runs. Its preimage includes the Reconciliation Timestamp, so the requirement was unsatisfiable; the Reconciliation Identifier is the reproducible index and always was. states how a reconciliation is commissioned. The document imposed obligations on "the response to the request that commissioned it" without defining that request anywhere. states who an auditor is. Four requirements were justified by what an auditor could reproduce, and the auditor was not a party this document admitted; an Audit Identity is now declared in a Bilateral Register Agreement, so that the audited party cannot choose its auditor after the facts are known. Several corrections follow from checking this document's claims about other specifications against those specifications. The deterministic CBOR encoding every digest here depends on is that of Section 4.2.1 of , which is now a normative reference; RFC 9052 narrows those requirements to COSE's own signing structures and states no map-key ordering rule, so the previous citation did not support what was built on it. , , and are referenced rather than named in prose. no longer attributes an Identity Manager or an Aggregator role to , which defines neither. no longer presents "capsule" as that draft's term. An unsourced claim about agreement on twenty-two pinned conformance vectors is removed, that draft having frozen none. The EU consolidated financial sanctions list and the OFAC SDN list are retargeted at the resources that actually publish them. Three further sections follow from those. pins the tree both Merkle roots in this document use, with domain separation and an inclusion- proof encoding, so that a proof produced by one implementation verifies under another. gives the Sovereign Re-Notification an artefact, a payload, a media type, a delivery endpoint and a retry obligation; it was a MUST with none of those in -02. states the disclosure model and the residual risks this revision accepts rather than leaving them to be inferred -- the subject has no standing in this protocol, an Audit Identity reads broadly, and the published ledger head discloses a deployment's size at the notarisation interval. Every digest preimage and signature payload in the document is now pinned to a CBOR array with a normative field order and null-substitution for absent fields: the Reconciliation Output and its Sealing Signature, the Partial Attestation, the Per-Register Claim Projection, the ledger entry, the Post-Seal Evaluation Record, the Non-Answer Statement, the Ledger Head Statement, the Evaluation Sweep Statement and the read response. -02 left several of them as "the canonical serialisation of the foregoing", which is not a preimage two implementations can agree on. Homomorphic Aggregation Mode is removed and Hash-Linkage is the only mode. The mode named no primitive, had no class in the Cryptographic-Primitive-Upgrade Path for one to be declared in, and defined no encrypted-contribution structure; and the reconciliation server must read every per-register verdict in the clear in any case, to verify the register's signature, recompute the Query Binding, check the echoed Policy-Version Hash and apply re-typing. The privacy property the mode advertised was therefore not available under it, and ARP's actual minimum-disclosure property -- controlled projection, and a Partial Attestation payload that discloses of the subject only a verdict, a divergence axis, the applied parameters and a digest -- is unaffected by its removal. Four homomorphic-* Aggregation-Method Descriptors go with it. The interface between the reconciliation server and a sovereign register is now stated to be out of scope, and the claim that enumerating the Per-Register Claim Projection lets two register operators build interoperable endpoints is withdrawn. Enumerating a structure is not specifying a binding. That leg -- an endpoint, a media type, and a COSE_Encrypt construction pinning the AEAD and its authenticated additional data -- is the principal item this revision leaves for the next.

Ways the protocol could be gamed, closed 's query budget is now measured per accountable principal per subject. A budget shared across requesters is exhausted for everyone by any one of them -- including an unidentified agent -- which forced every reconciliation about that subject to indeterminate for the interval. The countermeasure was a denial of service. Exhaustion now refuses the register and not the reconciliation, which resolves a contradiction in -02: the old text refused the reconciliation and then recorded a Non-Answer Reason in an Output that consequently did not exist. A register-attested Non-Answer Reason now requires a Non-Answer Statement signed by that register over the projection values and the reason, and records which reasons are register-attested and which are server-observed. Without it a register-refused was an unattested assertion by the party that transmitted the projection, and a server could suppress a match by claiming the register had declined. A server can still downgrade a reconciliation by asserting a server-observed reason and the document says so; what it can no longer do is dress suppression as an act of the register. is new. Every trigger of retroactive evaluation was server-observed, every decision to run was the server's, and nothing recorded that a sweep had happened -- so "we evaluated and found no change" and "we never evaluated" were the same observation from outside. A signed Evaluation Sweep Statement per sweep, notarised on the head interval, makes the absence of one an assertion the operator has to make. A Source-Data Version publication is a public event with a public timestamp; an operator with no Statement covering one has not evaluated, which is now checkable. The Verdict Arithmetic is resolved by the reconciliation server from policy, keyed on the predicate and the regimes the requester names. -02 read as though the requester declared the operator and its threshold in its own claim, which would let it choose the verdict: disjunction over five registers and threshold-count with a threshold of five differ only in which answer they return over the same contributions. Naming a regime is a claim about which law applies and the requester is accountable for it; selecting an operator is a determination about how evidence combines, and the deployment makes it. source-class-quorum now carries its per-class threshold into the Output as well as its partition, without which it was as irreproducible as carrying neither. The Requester-Binding gains a fourth class, agent-key-verified, for an agent whose signing key verified but whose asserted principal was not corroborated. -02 recorded key possession and principal binding as one fact. An agent that signs correctly has shown it is the same agent as last time and not that any accountable party stands behind it; recording that as agent-verified overclaimed to every downstream reader and recording it as agent-unverified discarded something real. states what revocation of a Verified Principal Credential does and does not reach. It is not detected in the hot path and this document does not pretend to put it there; what it does is bound the window, by requiring an Audience Member to read continuations before relying past the Reliance Horizon. Reliance years later on an Output whose principal was disowned the following week is the case that matters, and -02 left it open. The Override Record is enumerated, carries an Override Ground from a new registry, and is signed by the authorising operator rather than by the server. A record the server signs attests only that the server says an operator authorised a bypass. It names that operator in the clear, which is consistent with : blinding protects the published Ledger, and the Output is confidential to its Audience Set. Retroactive Evaluation now triggers on a new Source-Data Version. It previously triggered only on a Pattern Library or Policy Version change, so a sanctions list republication -- the case was written for -- fired nothing. A material change now includes a transition between decisive values: a no-match becoming a match is the case the motivating domain cares most about, and the earlier definition omitted it. Homomorphic Aggregation Mode was restricted in -02 and is removed in -03; see the -03 entry above. The Pattern-Library Version Identifier is no longer bound as authenticated additional data: registers are never told the pattern-library version, so binding it either failed universally or was supplied by the party that chose it. The Reconciliation Hash is taken over deterministic CBOR rather than , because the Output is CBOR and several fields are byte strings for which JSON has no type. Regulator Portal scope is the intersection across agreements rather than the union, which had let one permissive agreement widen access to a stricter register's reconciliations. The Freshness Timestamp is now enumerated before the signature line in and is therefore covered by it. It was listed after the signature in earlier revisions, and both replay defence and the new freshness-versus-skew distinction depend on it being signed. Not adopted: a statement that a reference implementation is forthcoming. It does not exist yet, and a draft should not carry a claim about an artefact a reader cannot check. When it is published it will be cited by repository and commit alongside the conformance vectors it is checked against.

Since draft-hillier-scitt-arp-01 This revision closes canonicalisation ambiguities identified by running an implementation of -01 against two published conformance corpora -- the EMILIA clean-room frozen-v1 agent-action corpus and the Noa AI-agent-receipt corpus -- states the role of the Appendix D subject digest explicitly, and corrects a number of requirements that were unsatisfiable, untestable or out of scope as written in -01. The harness and its machine-readable results were posted to the SCITT mailing list.

• is now a NORMATIVE reference. -01 named JCS in without identifying which JCS; the string "8785" did not occur in -01 at all. Agreement with a deployed profile depended on both parties having independently selected . It is now an obligation rather than a coincidence.
• The Canonical Claim in now pins its member-sort code unit to UTF-16, per Section 3.2.3 of . -01 said "lexicographic sorting of object keys", which does not determine the ordering of member names outside the Basic Multilingual Plane.
• Number rendering now cites Section 3.2.2.3 of . -01 cited "canonical JSON RFC 8259 number rendering"; RFC 8259 defines no canonical number rendering, and was an informative reference in -01.
• "Stripping of undefined values" is replaced by a statement about absent members, JSON having no undefined value to strip.
• New states that the Claim Hash and subject_digest are distinct constructions that MUST NOT be substituted for one another, and records the two observed COLLISION cases (Normalization Form D against Form C, and U+212B against U+00C5) in which a substitution fails silently rather than visibly.
• New states what subject_digest is and what it is not, which -01 left to be inferred. subject_digest is a content digest: collision-resistant over content, and therefore NOT stable under the variation an action type permits. Measured: five conforming instances of one registered action type, each accepted by that type's reference issuer and differing only in content the type declares OPTIONAL, produced five distinct subject digests. The section now separates the case the construction supports -- capsules over one shared serialisation, which is what composes -- from the case it does not, and requires a profile needing the latter to pin its member set or to join on a material identifier the action type declares. It also forbids describing a content digest as a correlation key without saying which case is relied on.
• The order of canonicalisation operations in is now normative. Normalization Form C is applied BEFORE the member sort. The two do not commute: for an object whose member names are U+0041 U+030A and "B", normalising first and sorting first produce different Claim Hashes. -01 gave the operations as an unordered list.
• remains an informative reference. composes over the capsule slots it defines and would cite it normatively, but it is an individual draft; making it normative now would create a publication dependency. The same applies to . The status of both references will be revisited as those documents progress.
• requires that a correlation digest carried on the wire identify its construction, and requires that such an identifier not commit to facts which do not affect the serialised bytes, so that two implementations producing identical bytes share an identifier.
• additionally requires that a correlation identifier over a typed action object be emitted only after the object validates against a pinned definition of its type.

Reference and source corrections in this revision:

• The SCITT Architecture reference is now and the COSE Merkle tree proofs reference is now . -01 cited both as Internet-Drafts; both have since been published as RFCs.
• The Web Bot Auth architecture reference is replaced. -01 cited draft-meunier-web-bot-auth-architecture, which has been replaced by . , which defines the signature-agent card, is retained. The directory the Signature-Agent header names is defined in , so no separate directory reference is carried.
• The document date, RFCXML version and submission type are declared in the source, and keyword is a single YAML sequence.
• A note to the RFC Editor records the downref explicitly, so that it can be called out at IETF Last Call per rather than found there.
• now REQUIRES that all composed capsules carry one shared action serialisation, established by the authorising party and echoed verbatim by later attesters, and states that a capsule's own account of the action travels in its payload rather than in subject_digest. -01 left the shared-serialisation condition implicit, which is the condition the digest depends on.
• The determinism requirement is scoped to the Reconciliation Output and to the Claim Hash, Reconciliation Hash and Policy-Version Hash; -03 removes the Reconciliation Hash from that set, as the -03 entry above records. -01 required bit-for-bit identical Settlement-Layer Ledger entries, which the entry's own sequence number, timestamp and prior-entry hash make unsatisfiable.
• The Claim Hash is pinned to SHA-256 in Canonical Claim Ingestion. -01 named the algorithm only in an appendix, leaving a parameter the construction identifier is required to commit to unstated in the normative body.
• Claim equality is stated over canonical field values, and declared array order is significant. -01 required semantically-equivalent claims to hash alike without defining semantic equivalence, which no implementer could test.
• The Per-Register Claim Projection is defined as the nearest permitted ancestor predicate rather than a greatest lower bound, which the Predicate Taxonomy -- a tree -- does not have, and the projection function now fails explicitly on an ambiguous or unreachable walk rather than choosing.
• The Settlement-Layer Ledger entry carries an OPTIONAL Source-Reconciliation-Output Identifier, which the retroactive re-evaluation example already relied on and the entry's closed field list did not admit.
• freshness-stale is added to the Divergence-Axis controlled set, and server-recorded axes are stated to travel in the Reconciliation Output rather than in a register's signed payload, which the reconciliation server cannot modify.
• COSE header labels are requested from IANA rather than asserted as a vendor-private range, and an IANA registry is requested for Divergence-Axis values.
• The examples are de-identified. Register identifiers are illustrative and no bilateral agreement with any named authority is asserted.
• Two independent implementations of an -based digest construction, one in Go and one in Python and sharing no source, were measured as agreeing byte-for-byte on 24 generated inputs selected to exercise absent-field normalisation, arrays, string escaping, UTF-16 member sorting and both integer bounds. Two implementations derived from one source would have demonstrated code identity rather than agreement, which is why the pair is named. That is the outcome argues for: one identified construction per digest role, committing to the parameters that affect the serialised bytes and to nothing else.

Since draft-hillier-scitt-arp-00

• Added a fourth motivating deficiency (unverifiable requester identity in an agentic setting) to the Introduction.
• Added a new pipeline subsystem, Requester Identity Binding and Agent Friend-or-Foe (IFF) Gate, and renumbered the pipeline to twelve subsystems.
• Added the agent: predicate branch, a new Agentic Principal Reconciliation section, and the divergence axes agent-principal-unverifiable, agent-credential-absent, and agent-impersonation-suspected.
• Added Requester-Binding to the Policy-Version Hash commitment and a requester-binding-class descriptor to the Settlement-Layer Ledger entry.
• Bound ARP to HTTP Message Signatures and Web Bot Auth for signed agent requests, and added an Agent Impersonation security consideration.
• Replaced the stale scitt-receipts reference with COSE Receipts and added the SCITT Reference APIs ; Hash-Linkage Aggregation now emits COSE Receipts.
• Described the Evidentiary Provenance Manifest's optional carriage as a COSE-enveloped Verified-Principal-Credential evidence container.
• Extended Retroactive Evaluation to treat credential revocation as a material change, and added a new IANA header label and worked agentic example.
• Added the motivating agentic-containment failure class to the Introduction and framed real-time reconciliation of claimed-versus-actual conduct as a first-class property, distinct from after-the-fact forensic reconstruction.
• Added a Composition with Agent-Action Accountability Capsules section reconciling heterogeneous CAN/WHO/WHAT/AUDIT capsules over a shared subject digest into a producer-agnostic verdict, with a worked divergent agent-action example.
• Added the agent-action-scope-divergence divergence axis.
• Removed two unused informative references (JWS, JWT).