]> VERAX TEKNOLOJI LIMITED SIRKETI

Turkey e.dogru@cedulon.com

sec Cedulon agent receipt policy SCITT This document defines the Cedulon Protocol, an audit layer for agent-to-agent commerce. Payment rails such as HTTP 402 flows (x402) and mandate protocols (AP2) already move value. They do not, by themselves, produce a fail-closed policy check and a signed spend receipt that a verifier can reconcile against a rail extract. Cedulon specifies a Trade Manifest (signed offer before payment), a Policy Decision Point with default deny, a Spend Receipt (COSE/CWT claim set after a gated payment), epoch checkpoints, and rail-extract reconciliation. The reconciliation shows that no settlement on the extract lacks a receipt and no settled receipt is absent from the extract. That result is unconditional only when the verifier pins the rail key out of band and states the period under audit; otherwise the document requires it to be reported as conditional. Checkpoints carry the suppression guarantee, so this revision profiles the checkpoint as a Signed Statement, gives the verification algorithm a step that consumes the transparency receipts returned for checkpoints, names what a witness holding a checkpoint the presented chain omits reports, brings equivocation within reach by comparing recorded copies against the presented chain, and states how checkpoint totals may be withheld without withholding the fact that they were. It also defines a Dispute Evidence Bundle (evidence, not an award) and optional SCITT anchoring. Cedulon is not a competitor to x402 or AP2; it sits above them.

Introduction Note to Readers: This document is submitted as Informational. The author's eventual intended track, if the work is taken up, is a Standards Track profile of COSE and CWT for agent-spend receipts. This -02 does not claim IETF consensus. Agents can now pay. Open HTTP 402 protocols attach stablecoin settlement to ordinary requests. Card networks and processors issue agent-scoped tokens. Google's Agent Payments Protocol (AP2) binds user intent to signed mandates. What is missing is an interoperable audit layer: a machine-checkable answer to "was this spend allowed by policy, against which offer, and what bytes were delivered?" Without that layer, a prompt-injected or looping agent can drain a rail that has already accepted a valid signature. A counterparty can ship the wrong artifact. A transparency log, if used at all, is proprietary. Cedulon fills that gap. It does not clear funds, hold custody, or operate a payment facilitator. An optional escrow actor is defined only as a third-party role interface (). Implementations of this specification MUST NOT take custody of funds or operate escrow (MUST-T8-custody). The control is an old one. Reconciling an internal ledger against an external statement is what double-entry bookkeeping made routine, and signing the artifacts on both sides is Grigg's triple-entry idea . Neither is claimed here. What this document contributes is an open wire profile for that control in a setting where the parties are software: a COSE receipt shape, an extract shape, a checkpoint chain, and a verification algorithm precise enough that two implementations reach the same finding on the same evidence. The novelty is interoperability, not the idea. Neighbor drafts are complementary, not substitutes. draft-bates-atp covers tamper-evident causal lineage as a signed DAG. Cedulon is the completeness layer: a spend that never produced a receipt is visible when an authenticated rail extract is reconciled (MUST-T10-1).

Terminology 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 used:

Trade Manifest:

A signed statement produced before payment. It binds a description of goods or service, price, currency, acceptance-criteria hash, cancel condition, expiry, and an optional AP2 mandate reference.

Policy Decision Point (PDP):

The function that evaluates a structured spend request against stored policy. The default is deny.

Spend Receipt:

A signed statement produced after a gated payment attempt. It binds payer, payee, amount, currency, policy hash, manifestHash or an explicit noManifest flag, rail payment reference, timestampMs, nonce, prevReceiptHash, and outcome.

Receipt Issuer:

The party that signs Spend Receipts.

Anchor:

An optional SCITT Transparency Service that registers a signed statement and returns a COSE receipt .

Dispute Evidence Bundle:

A package of the Trade Manifest, the Spend Receipt, and a delivery hash. It is evidence for a later human or legal process. It is not an arbitral award and not an escrow release.

Decision Token:

A portable, single-use PDP allow encoded as COSE_Sign1. The claim set binds requestHash, policyHash, expiryMs, nonce, and singleUseId. See .

Rail Extract:

An authenticated list of settlement records for one account, one rail, and one time window. See .

Architecture Cedulon has three control-plane objects and one optional log:

PDP --allow/deny--> x402/AP2 rail | v Receipt Issuer --> Spend Receipt | v Anchor / SCITT (optional) ]]>

The payer agent never talks to the rail except through an adapter that calls the PDP first (MUST-T5-1).

Policy Decision Point The PDP evaluates structured fields only (MUST-T1-1): amount, currency, payee, tool identifier, nonce, optional manifest hash, and evaluation time. It applies limit, velocity, and scope checks (MUST-T2-1, MUST-T2-2). If the PDP is unreachable, uninitialized, or throws, the result is deny (MUST-T2-3). Denied attempts do not increment success counters (MUST-T2-4). An allow produces a Decision Token whose requestHash covers six fields: amount, currency, payee, tool, nonce, and manifestHash (MUST-T3-4, MUST-T6-1). The token is a COSE_Sign1 object (MUST-T6-4), is single-use (MUST-T6-2), and MAY be carried to the adapter that performs settlement.

Receipt Issuer After the adapter attempts settlement (success or a recorded deny that still needs an audit trail for an allowed-then-aborted path), the Receipt Issuer signs a Spend Receipt over a canonical encoding (MUST-T4-1). Verifiers reject bad signatures and byte mismatch (MUST-T4-2).

Anchor / SCITT Parties MAY register the signed receipt (or a privacy-preserving hash encoding) as a SCITT Signed Statement and attach the COSE receipt (MAY-T4-6). This document does not operate a Transparency Service.

Trade Manifest A Trade Manifest is the commerce analogue of a promise: it is issued before value moves. It is conceptually symmetric to a later Spend Receipt (promise then proof), and it MAY carry an AP2 mandate hash so that user intent and the Cedulon offer stay linked (SHOULD-T8-5). A Trade Manifest MUST bind all of the following (MUST-T8-1): goods or service description price (integer minor units, encoded as a decimal string matching 0|[1-9][0-9]*) currency (ISO 4217 alphabetic or a documented token identifier) acceptance-criteria hash (SHA-256 of the exact delivery bytes or of a declared schema instance) cancel condition (opaque string agreed by the parties) expiry (POSIX milliseconds, expiresAtMs) It MAY include ap2MandateHash. The corresponding CBOR label is always present; a missing mandate is encoded as CBOR null. The manifest is COSE_Sign1 over a deterministic CBOR claim map (). manifestHash is the SHA-256 of the signed COSE bytes (MUST-T8-7). A spend bound to a manifest MUST be denied if the requested amount or currency differs from the manifest (MUST-T8-2) or if the manifest is expired (MUST-T3-3). A spend that is not bound to a verified manifest MUST be marked noManifest on the receipt and MUST still pass limit, velocity, and scope checks (MUST-T1-2). An implementation MAY refuse all noManifest spend (MAY-T1-4).

Spend Receipt The Spend Receipt claim set is carried in COSE_Sign1 wrapping a CWT-compatible map . New receipts MUST use the COSE profile (). Claims (MUST-T4-3, MUST-T4-4, MUST-T4-7): Claim Description payer Payer agent identifier payee Payee identifier amount Minor units as a decimal string 0|[1-9][0-9]* currency Currency identifier policyHash SHA-256 of the canonical policy document (lowercase hex) manifestHash SHA-256 of the signed manifest COSE bytes, or null when noManifest is true noManifest Boolean; MUST be true if and only if manifestHash is null x402PaymentRef Rail payment reference, or null timestampMs POSIX milliseconds nonce Unique spend nonce; at least 128 bits of randomness; unique in the issuer scope prevReceiptHash Previous receipt hash, or null for the first receipt (SHOULD-T4-5) outcome settled or aborted A receipt with outcome = settled MUST have a non-null x402PaymentRef (MUST-T4-7). An aborted receipt MUST NOT be added into checkpoint totals. All twelve labels in are always present. An empty optional value is encoded as CBOR null, never by omitting the label. receiptHash is the SHA-256 of the receipt's signed COSE bytes, encoded as lowercase hex. Verifiers MUST reject a receipt if the signature fails or if the decoded claim map does not match the presented claims (MUST-T4-2).

Optional payee countersignature A payee MAY attach a countersignature over the issuer's signed Spend Receipt (MAY-T8-9). The profile uses a detached COSE_Sign1 whose payload is a CBOR map with a single private-use label: Label Claim CBOR type -70401 receiptCose bstr (exact issuer COSE_Sign1 bytes) The countersignature uses the header profile in and content type application/cedulon-countersign+cbor. This is a second Sign1 object, not RFC 9052 Countersignature0 (unprotected-header label 11). Countersignature0 would write into the issuer object and change receiptHash after issue, breaking the receipt chain. A detached Sign1 keeps the issuer bytes stable, reuses kid and content-type, and is absent by simply omitting the sibling object. Absence of a countersignature MUST NOT invalidate the issuer receipt (MAY-T8-9). If a countersignature is present, a verifier MUST reject it when the signature fails, when kid or content type does not match the configured payee key, or when label -70401 is not the issuer COSE bytes (MUST-T8-8). The identifier countersign-bad SHOULD be used for this condition. A Dispute Evidence Bundle that includes a verified countersignature has stronger evidence that the payee accepted those bytes; the bundle is still not an award (MUST-T8-4).

COSE Profile This profile uses deterministic CBOR Section 4.2.1 (definite lengths, shortest integer form, map keys sorted in bytewise lexicographic order of their encoded keys). Implementations MUST encode only the types used by Cedulon claim maps: null, bool, unsigned and negative integers, UTF-8 text, byte strings, arrays, and maps (MUST-T4-1).

Claim labels Registered CWT claims are not required in -02. Cedulon uses CWT private-use integer labels less than -65536 so that the profile does not occupy the 100-110 registry range. Receipt labels (MUST-T4-3, MUST-T4-4, MUST-T4-7): Label Claim CBOR type -70001 payer tstr -70002 payee tstr -70003 amount tstr -70004 currency tstr -70005 policyHash tstr (lowercase hex SHA-256) -70006 manifestHash tstr / null -70007 noManifest bool -70008 x402PaymentRef tstr / null -70009 timestampMs uint -70010 nonce tstr -70011 prevReceiptHash tstr / null -70012 outcome tstr (settled / aborted) Checkpoint labels (MUST-T11-1): Label Claim CBOR type -70101 epoch uint -70102 startMs uint -70103 endMs uint -70104 receiptCount uint -70105 chainHeadHash tstr / null -70106 totals map tstr -> tstr / null -70107 prevCheckpointHash tstr / null Manifest labels (MUST-T8-1): Label Claim CBOR type -70201 description tstr -70202 amount tstr -70203 currency tstr -70204 acceptanceCriteriaHash tstr -70205 cancelCondition tstr -70206 expiresAtMs uint -70207 ap2MandateHash tstr / null Decision Token labels (MUST-T6-4): Label Claim CBOR type -70301 requestHash tstr -70302 policyHash tstr (lowercase hex SHA-256) -70303 expiryMs uint -70304 nonce tstr -70305 singleUseId tstr

COSE_Sign1 headers The protected header MUST be a deterministic CBOR map containing (MUST-T4-1, MUST-T4-8): 1 (alg) = -19 (Ed25519, ; the generic EdDSA value -8 from is deprecated for this profile) 3 (content type) = a tstr that distinguishes the payload: application/cedulon-receipt+cbor, application/cedulon-checkpoint+cbor, application/cedulon-manifest+cbor, application/cedulon-decision+cbor, or application/cedulon-countersign+cbor 4 (kid) = bstr, mandatory. The profile computes kid as the first eight bytes of SHA-256 over the issuer's SubjectPublicKeyInfo DER. A verifier MUST obtain the public key from an authenticated channel (preconfigured issuer set, directory, or transparency statement) and MUST reject a message whose kid does not match that key. The unprotected header MUST be empty. The payload MUST be the CBOR encoding of the claim map. The signature is Ed25519 over the COSE Sig_structure ["Signature1", protected, h'', payload].

Decision Token A Decision Token is the portable encoding of a PDP allow. It is COSE_Sign1 with the header profile in and the labels in . All five labels are always present (MUST-T6-4). requestHash MUST be the six-field hash defined for the PDP (MUST-T6-1). policyHash MUST be the SHA-256 of the canonical policy document the PDP evaluated. expiryMs is a Unix time in milliseconds after which the token MUST be treated as expired (SHOULD-T6-3). nonce is the request nonce. singleUseId is the identifier consumed on the first settlement attempt (MUST-T6-2). A party that accepts a Decision Token MUST reject it if the signature fails, if kid does not match a configured PDP key, if the content type is not application/cedulon-decision+cbor, if the decoded claim map does not match the presented claims, or if expiryMs is in the past (MUST-T6-5).

Rail Extract Profile A verifier checks completeness against a rail extract, not against the issuer's own receipts alone (MUST-T10-7).

Record schema Each settlement record MUST contain: Field Type ref tstr (rail payment reference) amount tstr matching 0|[1-9][0-9]* currency tstr timestampMs uint

Scope An extract is scoped to one account identifier, one rail identifier, and one half-open time window [windowStartMs, windowEndMs).

Authentication The mock rail in the companion implementation signs the extract with Ed25519 over a canonical encoding of the scoped body. A verifier MUST obtain the extract from the rail or from a signature the rail published (MUST-T10-7). A deployment that cannot do so is running the reconciliation against evidence it did not obtain independently, and MUST report the guarantee as conditional. A signature on an extract proves internal consistency, not origin: a key generated by whoever produced the object verifies against itself. The verifier therefore MUST obtain the rail's public key out of band and MUST verify the extract signature against that key rather than against any key the extract carries (MUST-T10-8). A verifier that holds no such key MUST treat the guarantee as conditional. Keys are compared as bytes. A verifier MUST compare the pinned key and the key that signed the extract by their SubjectPublicKeyInfo DER encoding, not by any text encoding of it, so that the same key presented in a different envelope still compares equal (MUST-T10-9). A pinned key the verifier cannot decode is a fault in the verifier's own configuration, not evidence about the extract, and MUST be reported as trust-key-unreadable rather than as a key mismatch. What a verifier emits for an extract it cannot authenticate depends on whether it stated an expectation. With no pinned key the verifier has asserted nothing, so an extract that does not carry a verifiable signature is unauthenticated-extract, a warning: completeness findings may still be computed, but the guarantee is conditional on the extract being authentic. With a pinned key the verifier has asserted what it requires, and an extract that fails to meet it is a failure rather than a caveat; see the verification algorithm for which finding applies. -00 defined only the first case, and readers of -00 should note that this revision makes the pinned case fail closed. See .

Scope agreement An extract declares a window and carries settlement records. The two MUST agree: a verifier MUST report every settlement record whose timestampMs falls outside [windowStartMs, windowEndMs) as extract-scope-mismatch, identified by that record's ref (MUST-T10-10). This check is about the extract's internal consistency and MUST be performed whether or not a rail key is pinned. A verifier that knows which account, rail, and window it is auditing MUST also check the extract against that expectation and MUST fail closed when the extract does not cover it (MUST-T10-11). An extract for another account or rail, or one whose window does not span the period under audit, cannot support a completeness claim about that period. A verifier that states no period leaves the extract free to define one, and an extract that reports on a millisecond balances as easily as one that reports on a month. Pinning a key establishes who signed; only a stated period establishes what the signature had to cover. A verifier that has not stated the period under audit therefore MUST emit unstated-audit-window and MUST treat the guarantee as conditional (MUST-T10-15), whatever else verifies.

Reconciliation and Epoch Checkpoints Completeness is the property that, given an authenticated rail extract, every settlement in the extract has a matching settled Spend Receipt, every settled receipt has a matching settlement, receipt and checkpoint hash chains verify, and checkpoint totals equal the sum of settled receipts in the checkpoint window. If a spend occurred without a receipt, the missing receipt is itself the evidence (MUST-T10-2). A checkpoint published with its totals withheld () cannot contribute the last of those to the property. It is not a violation of completeness and it is not a demonstration of it either: the comparison was not made, and a result that rests on a comparison nobody made is conditional (MUST-T11-12).

Checkpoint claims An epoch checkpoint MUST be COSE_Sign1-signed with the header profile in and MUST bind all of the following (MUST-T11-1): epoch, startMs, endMs, receiptCount, chainHeadHash, totals, and prevCheckpointHash. The checkpoint window is half-open [startMs, endMs) (MUST-T11-7). receiptCount MUST equal the number of receipts (settled and aborted) whose timestampMs falls in that window. chainHeadHash MUST equal receiptHash of the last receipt in that window, or null if the window is empty (MUST-T11-2). Where totals is present it MUST sum only receipts with outcome = settled; the one permitted absence is the signed redaction below. An issuer that publishes a checkpoint without its totals MUST encode totals as null in the signed payload (MUST-T11-12). An empty map is an honest zero for an empty window and is not a redaction. Because the redaction is inside the signature, it cannot be added to, or removed from, a checkpoint after signing. A verifier MUST NOT accept a redaction asserted anywhere but the signed payload (MUST-T11-13). A presentation-layer flag alongside a checkpoint is chosen by whoever presents it, which is the party under audit; honouring such a flag would let that party switch off the totals comparison for a checkpoint whose signed totals are wrong. The structural claims (epoch, startMs, endMs, receiptCount, chainHeadHash, prevCheckpointHash) MUST NOT be redacted: a checkpoint missing any of them does not decode, and a verifier MUST treat it as a failed checkpoint rather than as a redacted one.

Genesis and continuity The first checkpoint in a presented chain is the genesis checkpoint of that chain. Its prevCheckpointHash MUST be null. Epoch numbers MUST be consecutive integers. Adjacent windows MUST satisfy next.startMs = prev.endMs (MUST-T11-8). A later checkpoint that omits a prefix of earlier epochs (prefix deletion) is detectable only if an external witness (transparency log) has recorded the missing prefix (MUST-T11-9). Without that witness, T11 guarantees about suppression are conditional. -01 stated that dependency and stopped there: nothing in its verification algorithm read a transparency receipt, so the witness had no way to speak. This revision gives it one. A verifier that holds transparency receipts for the period under audit compares what the witness recorded against what the chain presented, and reports the difference under its own name (). A witness that holds a checkpoint the presented chain omits is not the same condition as a chain that leaves a gap in its own coverage, and the two MUST NOT be reported under one identifier (MUST-T11-11). The first says evidence is being withheld; the second says the evidence shown is incomplete. An operator who cannot tell them apart cannot tell an incomplete record from a concealed one.

The transparency witness A checkpoint registered with a Transparency Service is a Signed Statement whose payload is the checkpoint COSE object and whose content type is application/cedulon-checkpoint+cbor (). The service returns a receipt that binds the statement it recorded. A verifier MAY be given such receipts for the period under audit. It is a distinct input from the presented checkpoint chain, and supplying it is optional: a verifier given none performs the same steps, and reports the same findings, that it would if this input did not exist (MUST-T11-10). Supplying an empty set is not the same as supplying none. An empty set says a witness is configured and recorded nothing, which is itself reportable; absence says no witness was consulted. A receipt binds a statement hash, not a statement. The body is not carried by the receipt and a verifier will often not hold it. Two levels of checking follow from that, and they are not the same (MUST-T11-10). Every receipt MUST have its signature verified before it counts for anything. That is what establishes the hash as one the service signed for, and it is all that comparing recorded hashes against presented ones requires: the verifier computes the statement hash of each presented checkpoint itself. A receipt accompanied by the statement body carries more, and MUST be checked further before that body is relied on. The body's statement hash MUST equal the hash the receipt binds, and the body MUST itself verify as a checkpoint. A body that fails either check proves nothing and MUST be ignored rather than counted, while the receipt it came with remains usable for the hash comparison. Equivocation is the case that needs a body, because it compares claims rather than hashes. What such a receipt establishes, and what it does not, is worth stating plainly. It establishes that the service signed for that statement. Whether the statement is a member of an append-only log, and whether that log has ever equivocated, are properties of the service and its own proofs, not of Cedulon. A verifier that treats a signed receipt as proof of log membership is claiming more than the receipt carries.

Verification algorithm A verifier MUST perform all of these steps and MUST report every finding they produce (MUST-T10-1, MUST-T11-2). They are numbered for reference, not to require an evaluation order: no step short-circuits another, and an implementation may evaluate them in any order that produces the same set of findings. One data dependency is worth naming, because "any order" read naively would break it. Step 15 decides which transparency receipts, and which statement bodies, survive checking. Steps 14 and 16 consume what survives. An implementation that ran step 14 against unchecked bodies, or step 16 against unchecked receipts, would not produce the same set of findings, so that order is not among the permitted ones. Nothing else in this list feeds another step. When a step names an identifier in backticks, that identifier SHOULD be used for the condition in diagnostic output. The normative requirement is the behaviour: report the condition, identified by the ref or other handle given in the step. The identifiers are not an interoperability surface. Establish the subject of the audit. When an extract is supplied, the settlement records it carries are the ones reconciled; a settlement list from any other source MUST NOT be substituted for them (MUST-T10-12). If the caller supplies both and they differ, the verifier MUST report that the caller-supplied list disagrees with the extract, and MUST still reconcile the extract. The identifier extract-settlement-mismatch SHOULD be used for this condition in diagnostic output. Verify the extract signature against the out-of-band rail key (MUST-T10-8, MUST-T10-9). If no key is pinned, the verifier MUST treat the completeness guarantee as conditional (MUST-T10-7). The identifier unauthenticated-extract SHOULD be used for this condition in diagnostic output. If a key is pinned and cannot be decoded, the verifier MUST report that the pinned key is unreadable. The identifier trust-key-unreadable SHOULD be used for this condition. If a key is pinned and the signature does not verify against it, or verifies against a different key, the verifier MUST report that the extract is not signed by the pinned key. The identifier extract-key-mismatch SHOULD be used for this condition. A finding that puts the extract itself in doubt MUST prevent an unconditional guarantee. Check scope. The verifier MUST report each settlement record whose timestampMs falls outside the declared window, identified by that record's ref (MUST-T10-10). When the verifier states an expected account, rail, or window, it MUST report an extract that does not cover it (MUST-T10-11). The identifier extract-scope-mismatch SHOULD be used for both conditions. If the verifier stated no period, it MUST treat the guarantee as conditional (MUST-T10-15). The identifier unstated-audit-window SHOULD be used for this condition. Decode each Spend Receipt COSE_Sign1. Reject if Ed25519 verify fails, if kid does not match the configured issuer key, if the content type is not the receipt type, or if the decoded claim map does not match the presented claims (MUST-T4-2, MUST-T4-8). Scope the receipts. When an extract is supplied, only receipts whose timestampMs falls in the extract's declared window are reconciled against it (MUST-T10-16). A receipt outside that window is not a completeness failure against this extract; auditing a longer period requires extracts that cover it. Receipts remain subject to every other check regardless of window. Walk receipts in issuer order. The first prevReceiptHash MUST be null. Each later prevReceiptHash MUST equal receiptHash of the previous receipt. A miss MUST be reported as a break in the receipt chain. The identifier receipt-chain-break SHOULD be used for this condition. Index settled receipts and extract records by ref. A ref that appears more than once on either side MUST be reported as a repeated reference (MUST-T10-6). The identifier duplicate-ref SHOULD be used for this condition. For each ref that appears exactly once on each side, require a one-to-one match on ref AND amount AND currency (MUST-T10-1). Amount or currency mismatch MUST be reported as a settlement that does not match its receipt, identified by that ref. The identifier settlement-mismatch SHOULD be used for this condition. A settlement with no receipt MUST be reported as lacking a receipt, identified by its ref (MUST-T10-2). The identifier settlement-without-receipt SHOULD be used for this condition. A settled receipt with no extract row MUST be reported as a completeness failure (MUST-T10-3). The identifier receipt-without-settlement SHOULD be used for this condition. A settled receipt with a null rail ref MUST be reported as settled without a rail reference. The identifier settled-without-ref SHOULD be used for this condition. A ref already reported as repeating MUST still be reconciled by amount rather than dropped from the comparison (MUST-T10-13). For each currency under that ref, compare the total settled against the total receipted. A settled total that exceeds the receipted total MUST be reported as a settlement lacking a receipt, and the finding MUST state the unaccounted amount. The identifier settlement-without-receipt SHOULD be used for this condition. A settled total that is less than the receipted total MUST be reported as a settlement that does not match its receipt, identified by that ref. The identifier settlement-mismatch SHOULD be used for this condition. An amount on that repeating ref that cannot be parsed as an integer MUST be reported without abandoning the audit; the identifier malformed-amount SHOULD be used for this condition. A verifier MUST still report findings for the remaining records. Aborted receipts are not matched to extract rows and are not added to totals. Decode each checkpoint. Reject a failed signature, and reject a kid that does not match the key obtained for the checkpoint issuer, on the same terms as a receipt (MUST-T4-8). Require receiptCount, chainHeadHash, and totals to match the receipts in [startMs, endMs) as defined above (MUST-T11-2). The identifier checkpoint-total-mismatch SHOULD be used for a failed signature, a wrong receiptCount, or totals that disagree, and checkpoint-head-mismatch for a chainHeadHash that is not the last in-window receipt. If the signed totals is null, the verifier cannot perform the totals comparison for that checkpoint. It MUST report that the comparison was skipped and MUST treat the completeness guarantee as conditional; the absence of a comparison is not a passed comparison (MUST-T11-12). The identifier checkpoint-totals-redacted SHOULD be used for this condition. receiptCount and chainHeadHash MUST still be checked. A checkpoint that fails verification MUST NOT be treated as redacted, whatever it claims about its own totals. Every chained receipt MUST fall in exactly one checkpoint window. A gap or double count MUST be reported as a window coverage failure (MUST-T11-7, MUST-T11-8). The identifier window-coverage SHOULD be used for this condition. Walk checkpoints in epoch order. prevCheckpointHash MUST equal the SHA-256 of the previous checkpoint COSE bytes, or null for genesis (MUST-T11-4). The identifier checkpoint-total-mismatch SHOULD be used for a broken chain, which is the fourth condition its table row names. If two successfully verified checkpoints share an epoch number and have different hashes, the verifier MUST report equivocation (MUST-T11-3). The identifier equivocation SHOULD be used for this condition. The checkpoints compared here are those presented together with any carried by verified transparency receipts (step 15). Comparing only the presented chain cannot raise this finding: MUST-T11-8, applied in step 12, requires that chain's epochs to be consecutive, so no two of its members share an epoch. A copy recorded by a witness is where the second one is found. If transparency receipts were supplied, discard any whose signature fails (MUST-T11-10). The survivors are the recorded statement hashes used in step 16. Where a receipt also carries the statement body, discard that body unless its statement hash equals the one the receipt binds and it verifies as a checkpoint; the surviving bodies are what step 14 compares. Discarding a body does not discard its receipt. Compare the surviving witness records against the presented chain (MUST-T11-11). For each presented checkpoint with no surviving record, report that it is not anchored; the identifier checkpoint-not-anchored SHOULD be used. This is a warning: a witness may have been configured after the checkpoint was issued, and an operator's own gap is not evidence of concealment. For each surviving record whose statement is absent from the presented chain, report that a recorded checkpoint was withheld; the identifier checkpoint-withheld SHOULD be used. This is a finding and the audit MUST fail. The verifier MUST NOT report a withheld checkpoint as a window coverage failure (MUST-T11-11). If any finding remains that is not a warning (a warning is a condition that only makes the completeness guarantee conditional), the audit MUST fail (MUST-T10-4).

Finding codes The identifiers below are for diagnostic output. They are not an interoperability surface. A finding object that can be carried on the wire is outside the scope of this document and may be defined later. Two implementations interoperate when they accept the same inputs and fail or warn on the same conditions, not when they print the same strings. A condition that makes the audit fail is a finding. A condition that only makes the completeness guarantee conditional is a warning. Warnings MUST still appear in operator-facing output (MUST-T10-14). Code Effect Meaning settlement-without-receipt audit fails Extract row has no matching settled receipt, or a repeating ref settled more than it receipted receipt-without-settlement audit fails Settled receipt ref is not on the extract settlement-mismatch audit fails Same ref, different amount or currency, including a repeating ref that settled less than it receipted duplicate-ref audit fails Ref appears more than once on one side settled-without-ref audit fails outcome is settled and x402PaymentRef is null receipt-chain-break audit fails Signature or prevReceiptHash failed checkpoint-total-mismatch audit fails Totals, count, signature, or checkpoint chain failed checkpoint-head-mismatch audit fails chainHeadHash is not the last in-window receipt equivocation audit fails Two distinct hashes for one epoch window-coverage audit fails Gap, overlap, or non-adjacent / non-consecutive windows unauthenticated-extract guarantee conditional No pinned rail key, or the extract has no verifiable signature extract-key-mismatch audit fails Extract is signed by a key other than the pinned rail key, or does not verify against it trust-key-unreadable audit fails The pinned rail key could not be decoded; the verifier's configuration is at fault extract-scope-mismatch audit fails A record falls outside the declared window, or the extract does not cover the expected account, rail, or window extract-settlement-mismatch audit fails A caller-supplied settlement list disagrees with the extract; the extract is authoritative malformed-amount audit fails An amount on a ref already reported as repeating that could not be parsed as an integer unstated-audit-window guarantee conditional The verifier stated no period, so the extract defined its own countersign-bad audit fails Present payee countersignature failed verify checkpoint-withheld audit fails A verified transparency receipt binds a checkpoint the presented chain does not contain checkpoint-not-anchored guarantee conditional A witness was supplied and holds no verified receipt for this checkpoint checkpoint-totals-redacted guarantee conditional The checkpoint was signed with totals null, so the totals comparison could not be made A finding that puts the extract itself in doubt (extract-key-mismatch, trust-key-unreadable, extract-scope-mismatch, or extract-settlement-mismatch) MUST also prevent an unconditional guarantee, not merely fail the audit. An unconditional guarantee therefore requires all of: an extract, a pinned rail key the extract's signature verifies against, a stated period the extract covers, no finding that puts the extract in doubt, and no warning that withholds part of the comparison. A checkpoint whose totals were signed as withheld (checkpoint-totals-redacted) removes a comparison the guarantee rests on, and a presented checkpoint a supplied witness does not hold (checkpoint-not-anchored) leaves part of the chain unwitnessed. Either one makes the result conditional. Anything less than the whole list is conditional, and the report MUST say so. An implementation MUST make the guarantee and any warnings visible in whatever human-readable audit report it produces under this document, not only in a returned structure (MUST-T10-14). A report that says the books balance while withholding that the balance is conditional invites the reader to take a conditional result for an unconditional one. Checkpoints SHOULD be registered with a Transparency Service (SHOULD-T11-5). A test deployment MAY use an in-process append-only log as the witness (MAY-T11-6). Cedulon still MUST NOT take custody. The guarantee named above is about completeness against the extract, which is the subject of T10. It is not a claim that no checkpoint was suppressed. Suppression is the subject of T11, and a report MUST NOT be read as settling it when no witness was consulted: with no transparency receipts, the presented chain is self-consistent by construction and says nothing about what it left out (MUST-T11-9). A verifier that consulted a witness and found every presented checkpoint recorded, with nothing recorded that was not presented, has discharged T11 for the period those receipts cover, and for no longer.

Lifecycle Manifest. Parties sign a Trade Manifest (optional for metered API spend; required for goods with acceptance criteria). Policy check. The adapter submits a structured request to the PDP. Default is deny. An allow is a Decision Token (MUST-T6-4). Payment. On allow, the adapter performs the x402 (or other rail) exchange using exactly the decision fields (MUST-T6-1). The Decision Token is consumed (MUST-T6-2). A reused nonce is denied (MUST-T3-1, MUST-T3-2). A tampered or expired token is denied (MUST-T6-5). Receipt. The Receipt Issuer signs a Spend Receipt. Rail credentials MUST NOT appear in the receipt, logs, or tool results (MUST-T5-2, MUST-T7-1). Dispute Evidence Bundle. If delivery bytes do not match the acceptance-criteria hash, an implementation MUST be able to emit a bundle of manifest + receipt + delivery hash (MUST-T8-3). The bundle MUST NOT be described as an arbitral award or escrow release (MUST-T8-4).

Policy Semantics Policy is default deny. The engine understands three families of rule: Limit: maximum amount per payment; maximum cumulative amount per window (MUST-T2-2). Velocity: maximum number of allowed payments per window (MUST-T2-1). Scope: optional allow-lists for payee, currency, and tool name. Fail-closed: missing engine, crash, or exception yields deny (MUST-T2-3). Implementations SHOULD emit stable reason codes (SHOULD-T2-5). Decision tokens SHOULD expire after a short TTL (SHOULD-T6-3). The agent-facing spend interface MUST invoke the PDP and MUST NOT expose a parallel ungated rail call to the model (MUST-T5-1).

SCITT Anchoring A Receipt Issuer or relying party MAY construct a SCITT Signed Statement whose payload is either the Spend Receipt COSE object or a privacy profile () and register it with a Transparency Service . The service returns a COSE receipt . Embedding that receipt yields a Transparent Statement. Cedulon does not define a new transparency algorithm. An epoch checkpoint MUST be registrable on the same terms (MUST-T11-14). Its Signed Statement carries the checkpoint COSE_Sign1 object as the payload and application/cedulon-checkpoint+cbor as the content type, which is among the media types asks to have registered and which, until then, is a placeholder like the rest. Nothing else about registration differs from a receipt. This is a short section for a requirement -01 was missing, and the omission mattered more than its length suggests. -01 asked for checkpoints to be registered (SHOULD-T11-5) while profiling only the receipt here, so the object carrying the suppression guarantee had no stated form to be registered in. Two implementations could follow -01 to the letter and register incomparable things.

Privacy Considerations A public transparency encoding MUST support omitting or hashing payer and payee identifiers and MUST support amount redaction or bucket encoding (MUST-T9-1). Implementations MUST NOT write government-ID numbers, payment-instrument PAN, or street address into a public statement (MUST-T9-2). Default public anchors SHOULD publish policyHash, manifestHash, receiptHash, and timestampMs rather than full claims (SHOULD-T9-3). A private auditor MAY receive an unredacted receipt out of band (MAY-T9-4). The paragraph above counts receipt fields. A checkpoint publishes something a receipt does not: a per-currency total for a whole window, which discloses trading volume even when every individual receipt is redacted (MUST-T9-5). -01 gave no rule for it, so an implementation could publish that total, or withhold it in a way no verifier could recognise, and neither reading contradicted the text. The rule is the one stated in : totals MAY be withheld by signing it as null (MUST-T11-12), and only that form counts as a redaction (MUST-T11-13). The structural claims are not redactable, because a verifier that cannot read the window or the chain head cannot check anything at all, and a checkpoint that hid them would be indistinguishable from a broken one. Withholding is honest and it is also a cost: a verifier that cannot recompute the totals says so, and the completeness guarantee for that window is conditional. A deployment that wants an unconditional result publishes the totals; a deployment that wants the volume private accepts a conditional one. What a deployment MUST NOT do is obtain the unconditional result while withholding the evidence for it.

Security Considerations This section is authoritative for the protocol requirements in this document. The companion repository file THREAT_MODEL.md is informative and MUST NOT be read as overriding this section. Requirement identifiers take the form KEYWORD-Tn-k, where KEYWORD is MUST, SHOULD, or MAY, n is the threat number in this section, and k is a sequence number within that threat. MUST-T8-custody is the custody prohibition under T8. The tables below define the requirement text those citations refer to.

T1: Prompt injection leads to unauthorized spend ID Requirement MUST-T1-1 The PDP MUST decide from structured request fields and stored policy, not from model-generated prose. MUST-T1-2 A spend that is not bound to a verified Trade Manifest MUST be marked noManifest on the Spend Receipt and MUST still be subject to limit, velocity, and scope policy. SHOULD-T1-3 Hosts SHOULD require a human confirmation channel for first-use payees. MAY-T1-4 An implementation MAY refuse all noManifest spend.

T2: Runaway agent (loop spend) ID Requirement MUST-T2-1 Policy MUST express a maximum payment count per configured time window (velocity). MUST-T2-2 Policy MUST express a maximum amount per payment and a maximum cumulative amount per window. MUST-T2-3 If the PDP is unreachable, uninitialized, or throws during evaluation, the spend MUST be denied (fail-closed, default deny). MUST-T2-4 A denied attempt MUST NOT increment the allowed-spend counters as if it had succeeded. SHOULD-T2-5 Implementations SHOULD emit a stable reason code for velocity and limit denials.

T3: Replay of payment authority ID Requirement MUST-T3-1 Every spend attempt that the PDP allows MUST include a nonce that the implementation has not accepted before. MUST-T3-2 A second attempt that reuses a nonce MUST be denied. MUST-T3-3 A Trade Manifest MUST carry an expiry; a spend against an expired manifest MUST be denied. MUST-T3-4 A PDP allow decision MUST be bound to a hash of the request fields it evaluated and MUST be single-use. SHOULD-T3-5 Nonce stores SHOULD persist across process restart when the deployment is not a test fixture.

T4: Receipt forgery or repudiation ID Requirement MUST-T4-1 A Spend Receipt MUST be signed by the Receipt Issuer over a canonical encoding of its claims. MUST-T4-2 Verifiers MUST reject a receipt whose signature does not validate or whose canonical bytes do not match the signed payload. MUST-T4-3 A Spend Receipt MUST include payer, payee, amount, currency, policyHash, timestampMs, and nonce. MUST-T4-4 A Spend Receipt MUST include manifestHash or an explicit noManifest flag, never an ambiguous empty hash. Empty optional values are CBOR null; labels are never absent. SHOULD-T4-5 Receipts SHOULD form a hash chain (prevReceiptHash) so omission is detectable within one issuer stream. MAY-T4-6 Parties MAY register the signed receipt as a SCITT statement to obtain a COSE receipt. MUST-T4-7 A Spend Receipt MUST include outcome (settled or aborted). A settled receipt MUST have a non-null rail ref. Aborted receipts MUST NOT enter checkpoint totals. MUST-T4-8 COSE_Sign1 protected headers MUST use alg -19 (Ed25519), a mandatory kid, and a payload-specific content type. Verifiers MUST reject a kid that does not match the configured issuer key.

T5: Policy bypass via direct rail access ID Requirement MUST-T5-1 The agent-facing spend interface MUST invoke the PDP and MUST NOT expose a parallel ungated rail call to the model. MUST-T5-2 Rail credentials, wallet handles, and facilitator tokens MUST NOT be placed in tool results or prompts. SHOULD-T5-3 Hosts SHOULD run the PDP and signing keys in a process the model runtime cannot write. MAY-T5-4 A deployment MAY use OS or hardware isolation between the model and the PDP.

T6: TOCTOU between policy check and payment ID Requirement MUST-T6-1 Payment settlement MUST use the same six requestHash fields the PDP evaluated: amount, currency, payee, tool, nonce, and manifestHash. MUST-T6-2 An allow decision MUST be consumed on the first settlement attempt, success or fail-closed abort, and MUST NOT authorize a later different request. SHOULD-T6-3 Implementations SHOULD treat a decision older than a short TTL as expired. MUST-T6-4 An allow Decision Token MUST be COSE_Sign1 with CWT private-use labels -70301..-70305 (requestHash, policyHash, expiryMs, nonce, singleUseId) and content type application/cedulon-decision+cbor. MUST-T6-5 A party that accepts a Decision Token MUST reject a failed signature, a kid or content-type mismatch, a claim-map mismatch, or an expired expiryMs.

T7: Signing-key leakage ID Requirement MUST-T7-1 Secret key material MUST NOT appear in receipts, checkpoints, manifests, decision tokens, logs, or example output. MUST-T7-2 Example and test keys MUST be generated at runtime or stored as clearly fake fixtures, never as production secrets. SHOULD-T7-3 Production deployments SHOULD use an HSM or OS key store and SHOULD rotate keys. MAY-T7-4 Implementations MAY encrypt keys at rest.

T8: Counterparty price gouging or defective delivery ID Requirement MUST-T8-1 A Trade Manifest MUST bind goods or service description, price, currency, acceptance-criteria hash, cancel condition, and expiry. MUST-T8-2 A spend bound to a manifest MUST be denied if the requested amount or currency differs from the manifest. MUST-T8-3 If delivery bytes do not hash to the acceptance-criteria hash, the implementation MUST be able to produce a Dispute Evidence Bundle containing the manifest, the spend receipt, and the delivery hash. MUST-T8-4 The Dispute Evidence Bundle MUST NOT be described as an arbitral award or escrow release. MUST-T8-7 manifestHash MUST be the SHA-256 of the signed Trade Manifest COSE bytes and MUST NOT include the issuer public key encoding. SHOULD-T8-5 Manifests SHOULD reference an AP2 mandate hash when one exists. MAY-T8-6 Parties MAY add an optional escrow actor as a third-party role interface; this project MUST NOT implement custody. MUST-T8-custody Implementations of this specification MUST NOT take custody of funds or operate escrow. MUST-T8-8 If a payee countersignature is present, a verifier MUST reject it when the signature fails, when kid or content type does not match the configured payee key, or when the payload is not the issuer COSE_Sign1 bytes. MAY-T8-9 A payee MAY attach a detached COSE_Sign1 countersignature over the issuer receipt bytes. Absence MUST NOT invalidate the issuer receipt.

MUST-T8-custody Implementations of this specification MUST NOT take custody of funds or operate escrow. See also .

T9: PII leakage into the transparency log See also . ID Requirement MUST-T9-1 A transparency encoding MUST support omitting or hashing payer/payee identifiers and MUST support amount redaction or range/bucket encoding. MUST-T9-2 Implementations MUST NOT write raw government-ID, payment-instrument PAN, or street address fields into a public transparency statement. SHOULD-T9-3 Default public anchors SHOULD publish policyHash, manifestHash, receiptHash, and timestamp rather than full claim sets. MAY-T9-4 A private auditor MAY receive an unredacted receipt out of band. MUST-T9-5 A checkpoint discloses a per-currency window total, which the receipt-field rules above do not cover. Withholding it is governed by MUST-T11-12 and MUST-T11-13: null in the signed payload, and no other form of redaction honoured.

T10: Secret spend via rail bypass See . ID Requirement MUST-T10-1 A verifier MUST match each extract settlement to a settled receipt on ref AND amount AND currency. MUST-T10-2 A settlement with no matching receipt MUST be reported as a completeness failure identified by that settlement ref. MUST-T10-3 A settled Spend Receipt whose x402PaymentRef is not on the extract MUST be reported as a completeness failure. MUST-T10-4 An audit that has any fail-severity completeness finding MUST fail (non-zero status in the companion tool). SHOULD-T10-5 Hosts SHOULD still apply T5 (no ungated rail in the model process). Completeness does not replace prevention. MUST-T10-6 A ref that appears more than once among settled receipts or among extract rows MUST be reported as duplicate-ref. MUST-T10-7 A verifier MUST obtain the extract from the rail or from a rail signature. With no pinned rail key, an unverifiable extract MUST be reported as unauthenticated-extract and makes the completeness guarantee conditional. With a pinned key, see MUST-T10-8: the extract MUST fail closed rather than warn. MUST-T10-8 A verifier MUST obtain the rail public key out of band and MUST verify the extract signature against that key, not against a key the extract carries. Without such a key the guarantee is conditional. MUST-T10-9 Keys MUST be compared by SubjectPublicKeyInfo DER encoding rather than by any text encoding. A pinned key that cannot be decoded MUST be reported as trust-key-unreadable, not as a key mismatch. MUST-T10-10 Every settlement record whose timestampMs falls outside the extract's declared window MUST be reported as extract-scope-mismatch, identified by that record's ref. This check MUST run whether or not a key is pinned. MUST-T10-11 When the verifier states an expected account, rail, or window, an extract that does not cover it MUST fail closed as extract-scope-mismatch. MUST-T10-12 When an extract is supplied, the records it carries are the subject of reconciliation. A settlement list from another source MUST NOT be substituted; a disagreeing list MUST be reported as extract-settlement-mismatch. MUST-T10-13 A ref reported as duplicate-ref MUST still be reconciled by aggregate amount per currency, and a shortfall MUST state the unaccounted amount. An unparseable amount MUST be reported as malformed-amount without aborting the audit. MUST-T10-14 An implementation MUST surface the guarantee and any warnings in any human-readable audit report it produces, not only in a returned structure. MUST-T10-15 A verifier that has not stated the period under audit MUST emit unstated-audit-window and MUST treat the guarantee as conditional, because an unstated period leaves the extract free to define its own. MUST-T10-16 When an extract is supplied, only receipts whose timestampMs falls in its declared window are reconciled against it. A receipt outside that window MUST NOT be reported as a completeness failure against that extract. In MUST-T10-4, a completeness finding that makes the audit fail is distinct from a warning that only makes the guarantee conditional. The verification algorithm states that distinction by behaviour ().

T11: Checkpoint suppression or rollback ID Requirement MUST-T11-1 An epoch checkpoint MUST be COSE-signed and MUST bind epoch number, time window, receipt count, chain-head hash, per-currency totals, and the previous checkpoint hash. MUST-T11-2 Verifiers MUST reject a checkpoint whose signature fails, whose totals do not match settled receipts in the declared window, whose receiptCount is wrong, or whose chainHeadHash is not the last in-window receipt hash. Where the signed totals are null, MUST-T11-12 governs instead: there is no total to disagree with, the comparison is reported as skipped, and the count and chain-head checks still apply. MUST-T11-3 Two verified checkpoints for the same epoch with different hashes MUST be reported as equivocation. The checkpoints compared are those presented together with those carried by verified transparency receipts; the presented chain alone cannot satisfy this requirement, because MUST-T11-8 makes its epochs consecutive. MUST-T11-4 A broken checkpoint hash chain MUST fail verification. SHOULD-T11-5 Checkpoints SHOULD be registered with a Transparency Service when one is configured. MAY-T11-6 A test deployment MAY use an in-process append-only log as the witness. MUST-T11-7 Checkpoint windows MUST be half-open [startMs, endMs). Every chained receipt MUST fall in exactly one window. MUST-T11-8 Presented checkpoint epochs MUST be consecutive and adjacent windows MUST meet at endMs = next.startMs. MUST-T11-9 Prefix-deletion and suppression claims that go beyond the presented chain are conditional on an external transparency witness. A report MUST NOT present a completeness guarantee as settling suppression when no witness was consulted. MUST-T11-10 Transparency receipts are an optional, separate input. A verifier given none MUST behave as it did without this input. A receipt MUST have its signature verified before it counts for anything. Where a receipt also carries the statement body, that body MUST NOT be relied on unless its statement hash equals the one the receipt binds and it verifies as a checkpoint; a discarded body does not discard its receipt. MUST-T11-11 A verified receipt binding a checkpoint absent from the presented chain MUST be reported as a withheld checkpoint, and MUST NOT be reported as a window coverage failure. A presented checkpoint with no verified receipt, where a witness was supplied, MUST be reported and makes the guarantee conditional. MUST-T11-12 Withheld checkpoint totals MUST be encoded as null in the signed payload. A verifier MUST report that the totals comparison was skipped and MUST treat the guarantee as conditional; receiptCount and chainHeadHash MUST still be checked. MUST-T11-13 A redaction asserted outside the signed payload MUST NOT be honoured, and structural claims MUST NOT be redacted. A checkpoint that fails verification MUST NOT be treated as redacted. MUST-T11-14 An epoch checkpoint MUST be registrable as a Signed Statement carrying the checkpoint COSE object with content type application/cedulon-checkpoint+cbor.

Issuer self-attestation:

A Receipt Issuer that also produces the only copy of the extract can omit settlements. Completeness holds only against an extract the verifier obtained from the rail or from a rail signature.

Key rotation and revocation:

kid identifies the verification key. This -02 does not specify a revocation list. Verifiers MUST pin the issuer keys they accept and MUST stop accepting a kid after an authenticated revocation signal.

Timestamp trust:

timestampMs is issuer-asserted. Window assignment uses that field. A lying issuer can slide a receipt between windows. External timestamping of receipts is out of scope for -02; the checkpoint witness added here covers checkpoints, not receipt timestamps.

Collusion:

If the rail operator and the issuer collude, they can publish a matching extract and receipt set that hides a real-world settlement. Cedulon does not detect extract-external agreement.

Reversal, refund, and partial settlement:

State machines for reversal, refund, and partial settlement are out of scope for this revision.

Optional escrow role Parties MAY name an escrow actor in a Trade Manifest as a third-party role that holds funds under rules outside this protocol (MAY-T8-6). Implementations of this specification MUST NOT take custody or operate escrow (MUST-T8-custody).

IANA Considerations CWT claim labels need no assignment: this profile uses private-use integer labels below -65536. Media types do. This document defines five and makes their values a normative check inside a protected COSE header (MUST-T4-8, MUST-T6-5), so they cannot stay unregistered while that check stands. If this work is taken up, the following should be registered in the Standards Tree per : Media type Carries application/cedulon-receipt+cbor Spend Receipt claim set application/cedulon-checkpoint+cbor Epoch checkpoint claim set application/cedulon-manifest+cbor Trade Manifest claim set application/cedulon-decision+cbor Decision Token claim set application/cedulon-countersign+cbor Payee countersignature For each: encoding is binary CBOR ; security considerations are those in ; the change controller would be the IETF; the contact is the author of this document. Until registration, an implementation outside a closed deployment should expect these names to change, and readers should treat them as placeholders rather than as stable identifiers.

Implementation Status This section is to be removed before publishing as an RFC. RFC 7942 note.

Implementation:

A companion implementation with a runnable verification suite at https://github.com/dogrucanemek-alt/cedulon. The code is a profile of this document, not a second specification. This -02 is not an IETF working-group item.

Maturity:

Research code by a single implementer. Three readers have run the code on their own machines against a pinned commit and reported figures matching the author's: two from a clean clone of the whole suite, one re-running the published reproduction. That is byte-stability across environments, not an independent implementation, and the distinction matters: the same code agreeing with itself on three machines rules out a local accident and nothing more. One reader reports an independent implementation of the Signed Statement identity, kept deliberately separate from this codebase; no independent implementation of the reconciliation algorithm is known to the author.

Coverage:

The receipt, checkpoint, extract, reconciliation, and verification algorithm are implemented, including the transparency witness input, the withheld and not-anchored conditions, and signed totals redaction. Every requirement added in this revision is implemented and covered by a red-then-green case before appearing in this text. The witness used in the suite is the in-process append-only log that MAY-T11-6 permits; the implementation has not been run against a deployed Transparency Service, and it treats a receipt as a signature over a statement, not as a proof of log membership. The escrow role, reversal, refund, and partial settlement are not implemented.

Licensing:

Apache-2.0.

Contact:

The author of this document.

Experience:

Readers of -00 and -01 have reported defects in both, and each revision has been driven by what they found rather than by a plan. -01 fixed a bypass of the completeness claim and a gap about which key an extract is checked against. The defect behind this revision was reported against -01 by a reader who then had it independently confirmed by a second: the object carrying the T11 guarantee was not profiled for registration and was never read during verification. Repairing it turned up one more, found while checking the repair rather than reported: the first attempt asserted the totals redaction in a field outside the signature, which let a checkpoint with wrong signed totals be re-presented as redacted and silence the mismatch. That is the defect MUST-T11-13 now forbids, and it was the same shape as the bypass -01 was written to fix.

Note on distribution: the requirements in this document are implemented in the repository at the commit named in the release notes. The published @cedulon packages lag the repository: as of this revision the requirements added here are in the repository but not yet in a published package version, so a reader checking a claim against an installed package should read the repository instead, or confirm the package version carries the commit.

Changes from -01 This revision has one subject: the checkpoint, which carries the T11 guarantee against suppression and rollback, was not wired into anything that could discharge it. A reader of -01 set out the gap and a second reader confirmed it independently. Four things were wrong at once, and they were the same thing seen from four sides. The SCITT anchoring section profiled the Spend Receipt and not the checkpoint, so SHOULD-T11-5 asked for checkpoints to be registered without saying in what form (MUST-T11-14 now says). None of the steps of the verification algorithm read a transparency receipt, so a deployment could follow SHOULD-T11-5 to the letter and still have a verifier that never consulted the witness (steps 15 and 16 now do). MUST-T11-3, equivocation, could not fire at all: the only checkpoints compared were the presented ones, and MUST-T11-8 requires those to be consecutive, so no two of them can share an epoch. A second copy is found in a witness, and nothing brought one in. And the checkpoint binds a per-currency total for a window while the privacy section counted only receipt fields, so a window total could be published, or withheld, with no stated rule either way. The repairs are MUST-T11-10 through MUST-T11-14. The transparency receipt is a new optional input; supplying none leaves the verifier behaving exactly as in -01, which is deliberate, because the point of the witness is to add a claim that could not be made before, not to withdraw one that could. Two decisions inside those repairs are worth stating on their own, because a reader might reasonably have expected the other choice. A recorded checkpoint the presented chain omits gets its own identifier, checkpoint-withheld, rather than being folded into window-coverage (MUST-T11-11). The reporter asked which way it should go. Coverage says the record shown is incomplete; a withheld checkpoint says the party under audit is holding a record it did not show. An operator who sees one identifier for both cannot tell an incomplete record from a concealed one, which is the distinction the whole threat is about. A checkpoint with no receipt in a supplied witness is a warning rather than a failure. A witness may be configured after checkpoints have already been issued, and an operator's own gap in anchoring is not evidence that anything was concealed. The asymmetry is deliberate: what the witness holds and the chain does not is a finding, what the chain holds and the witness does not is a warning. One change is not a repair of -01 but of the first attempt at this revision, and it is recorded because the failure is instructive. Signed totals were first made redactable through a field carried alongside the checkpoint rather than inside the COSE payload. Anything outside the signature is chosen by whoever presents the object, which here is the party under audit, so a checkpoint whose signed totals disagreed with its receipts could be re-presented as redacted and the mismatch went unreported. Redaction is now inside the signature and a redaction asserted anywhere else MUST be ignored (MUST-T11-12, MUST-T11-13). This was the same shape as the bypass -01 was written to close: a check that a party under audit could switch off. Reversal, refund, partial settlement, and the escrow role remain out of scope and are still expected later, with no date. -01 said the same and this revision does not improve on it. The reporters are named in the Acknowledgments.

Evolution and Future Work (Informative) This section is a direction, not a commitment. The structures below are reserved in name only. Normative wire formats, tests, and threat-model MUST lines for them belong in later revisions (-03 or later), written with the same discipline as this -02.

Re-attestation profile Algorithms retire. A Spend Receipt or checkpoint signed under Ed25519 today may need a later verifier that no longer accepts -19. A companion seed sketches re-attestation: register the original COSE bytes as a SCITT Signed Statement and have a current algorithm countersign or receipt them. The principle is that structures outlive ciphers. The first concrete example is the profile's own move from generic EdDSA (-8) to Ed25519 (-19) in .

Streaming reconciliation Epoch checkpoints in this document are batch windows. A later revision may define a continuous, second-scale profile in which the same completeness relation is evaluated as settlements arrive, without waiting for an epoch close. That work does not change the matching rules in this document, and it did not arrive in this revision either.

Generalization Payment is the special case that this -02 implements. The same completeness calculus (an authenticated extract of consumed units reconciled to signed receipts) can apply to other consumable resources such as compute, data, or energy. This document does not specify those profiles.

Informative Notes on Adjacent Protocols x402 uses HTTP 402 to negotiate stablecoin payment. AP2 uses signed mandates as verifiable credentials. Cedulon does not replace either protocol. Profiles built on HTTP Message Signatures authenticate bots; they are not a spend receipt. draft-bates-atp is a lineage neighbor. It does not define rail-extract completeness. draft-vauban-x402-stark-receipts specifies complementary x402 receipt-format variants that a Cedulon Spend Receipt MAY carry as a rail proof; it does not define rail-extract completeness. draft-schrock-ep-outcome-binding compares authorized action bytes to independently observed effects; it does not define rail-extract completeness. draft-marques-asqav-compliance-receipts profiles access-control action receipts (the broader Acta family includes ); it does not define rail-extract completeness. draft-hopley-x402-compliance-receipt records an admission-time compliance decision; it does not define rail-extract completeness.

In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Federal Information Processing Standard, FIPS This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. This document describes elliptic curve signature scheme Edwards-curve Digital Signature Algorithm (EdDSA). The algorithm is instantiated with recommended parameters for the edwards25519 and edwards448 curves. An example implementation and test vectors are provided. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR), and CBOR Object Signing and Encryption (COSE) is used for added application-layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/value pair consisting of a claim name and a claim value. CWT is derived from JSON Web Token (JWT) but uses CBOR rather than JSON. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines a set of algorithms that can be used with the CBOR Object Signing and Encryption (COSE) protocol (RFC 9052). This document, along with RFC 9052, obsoletes RFC 8152. This specification refers to cryptographic algorithm identifiers that fully specify the cryptographic operations to be performed, including any curve, key derivation function (KDF), and hash functions, as being "fully specified". It refers to cryptographic algorithm identifiers that require additional information beyond the algorithm identifier to determine the cryptographic operations to be performed as being "polymorphic". This specification creates fully-specified algorithm identifiers for registered JSON Object Signing and Encryption (JOSE) and CBOR Object Signing and Encryption (COSE) polymorphic algorithm identifiers, enabling applications to use only fully-specified algorithm identifiers. It deprecates those polymorphic algorithm identifiers. This specification updates RFCs 7518, 8037, and 9053. It deprecates polymorphic algorithms defined by RFCs 8037 and 9053 and provides fully-specified replacements for them. It adds to the instructions to designated experts in RFCs 7518 and 9053. CBOR Object Signing and Encryption (COSE) Receipts prove properties of a Verifiable Data Structure (VDS) to a verifier. VDSs and associated Proof Types enable security properties, such as minimal disclosure, transparency, and non-equivocation. Transparency helps maintain trust over time and has been applied to certificates, end-to-end encrypted messaging systems, and supply chain security. This specification enables concise transparency-oriented systems by building on Concise Binary Object Representation (CBOR) and COSE. The extensibility of the approach is demonstrated by providing CBOR encodings for Merkle inclusion and consistency proofs. Traceability in supply chains is a growing security concern. While Verifiable Data Structures (VDSs) have addressed specific issues, such as equivocation over digital certificates, they lack a universal architecture for all supply chains. This document defines such an architecture for single-issuer signed statement transparency. It ensures extensibility and interoperability between different transparency services as well as compliance with various auditing procedures and regulatory requirements. This document describes a simple process that allows authors of Internet-Drafts to record the status of known implementations by including an Implementation Status section. This will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. This process is not mandatory. Authors of Internet-Drafts are encouraged to consider using the process for their documents, and working groups are invited to think about applying the process to all of their protocol specifications. This document obsoletes RFC 6982, advancing it to a Best Current Practice. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. This document describes a mechanism for creating, encoding, and verifying digital signatures or message authentication codes over components of an HTTP message. This mechanism supports use cases where the full HTTP message may not be known to the signer and where the message may be transformed (e.g., by intermediaries) before reaching the verifier. This document also describes a means for requesting that a signature be applied to a subsequent HTTP message in an ongoing HTTP exchange. x402 Foundation Google Agentic Commerce Vauban Research

Acknowledgments Vernon Wharff set out the defect this revision repairs: that the object carrying the T11 guarantee was neither profiled for registration nor read during verification, and that the equivocation requirement could not fire against a presented chain. He also asked the question that decided the shape of the repair, namely whether a recorded checkpoint absent from the chain deserves its own identifier or belongs under window coverage. Iman Schrock confirmed the finding independently and drew its boundary, keeping it separate from the extract-binding work already closed in -01. Iman Schrock and Pablo Play ran the -00 implementation against the pinned commit and reported the defects that produced -01. Iman Schrock found the two extract-binding defects, proposed the repair -01 adopts, later reran the posted -01 from a clean clone against its own pinned commit, and is also the author of , cited here as adjacent work. He is the reader whose independent implementation of the Signed Statement identity is noted in , and he asked for it to be kept separate from any cross-implementation claim about Cedulon; that separation is his and is recorded here as he stated it. Pablo Play found that a repeated reference hid the unaccounted amount, filed a written reproduction, and re-ran that reproduction against the pinned commit to confirm the figures quoted from it. Nicholas Templeman ran the suite from a clean clone on a different operating system and reported his figures, and classified his own run honestly as a repetition of the author's checks rather than an independent implementation. Walter Hawkins did not run it; he read the reported figures and pressed for the run to be stated precisely enough to be repeatable, which is why the conditions and not only the totals appear in . None of them reviewed this text, and any error in it is the author's. Field survey notes and the informative threat-model narrative in the companion repository helped shape the requirement identifiers used here. Those identifiers are defined in .

Appendix A. Test Vectors These vectors use RFC 8032 Ed25519 secret scalar #1 (fixture only; never a production key). Hex is lowercase. They MUST match the locked tests in the companion implementation. Receipt COSE_Sign1: Claims: payer=payer-1, payee=payee-1, amount=1, currency=USD, policyHash=aa, manifestHash=null, noManifest=true, x402PaymentRef=null, timestampMs=1700000000000, nonce=n100000000000000, prevReceiptHash=null, outcome=aborted. COSE_Sign1 hex (whitespace ignored; identical to the locked test):

Manifest COSE_Sign1: Body: description=fixture-goods, amount=1, currency=USD, acceptanceCriteriaHash=00, cancelCondition=none, expiresAtMs=1700000000000, ap2MandateHash=null. COSE_Sign1 hex (whitespace ignored; identical to the locked test):