| Internet-Draft | Agent Action Capsules | August 2026 |
| Mih | Expires 1 March 2027 | [Page] |
This document defines a SCITT statement profile for recording what an AI agent did: the Agent Action Capsule. A Capsule is a digest-committed record of one agent action carrying its verdict-level disposition (executed, blocked, denied, errored, timed out), the deterministic constraints that were evaluated, the effect that was committed together with a confirmed-effect binding that distinguishes a dispatched attempt from an observed result, and an honest human-in-the-loop flag. Capsules are identified independently of signing and MAY be authenticated by one or more COSE_Sign1 Producer Envelopes. Its Capsule ID can separately be made transparent by registration in a SCITT Transparency Service. A Capsule is recorded on every verdict, including refusals: a blocked or denied Capsule is the auditor-grade evidence that a gate worked.¶
This document is an individual submission. The intended venue for discussion is the SCITT Working Group (scitt@ietf.org).¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 1 March 2027.¶
Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
AI agents increasingly take actions with external consequences: writing records, sending payments, filing documents. Two distinct evidentiary questions follow. The question "was this action permitted?" is answered by authorization records produced before execution. The question this profile answers is different: "what did the agent actually do?" — including the cases where the answer is "it was stopped."¶
This document defines the Agent Action Capsule, its signer-independent identity, a COSE_Sign1 Producer Envelope, and a separate SCITT [RFC9943] registration statement for making the Capsule ID transparent. The Capsule is a digest-committed record of one agent action and its verdict-level disposition. The profile's central design commitments are:¶
The may/did distinction. A Capsule records what occurred, with an effect-state binding (Section 5.3) that structurally distinguishes "the effect was dispatched" from "the effect's result was observed and bound." A producer cannot present an attempt as a completion.¶
A Capsule on every verdict (Section 5.5.3). Capsules are recorded for refusals, blocks, errors, and timeouts — not only for executed effects. An evidence trail that records only successes is survivorship-biased and cannot prove its gates ever fired.¶
Independent verifiability. The substrate guarantees (envelope signature, registration, receipt) are SCITT's and are verified by reference; the agent-domain checks defined here (Section 6, Section 8.2) are deterministic and reproducible by any verifier from the record's own bytes, in two conformance classes (Section 7).¶
The term "Producer Envelope profile" means the exact COSE protected-header, payload, and signature constraints in Section 3.1. The Capsule JSON and its identity construction remain independently verifiable without an envelope.¶
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The Agent Action Capsule, a JSON record of one agent action with a signer-independent content identity.¶
The terminal outcome of one agent action — what the decision gate concluded and what is consequently known about the effect.¶
The digest-committed block within a Capsule recording how the decision was disposed: the gate outcome, who disposed it, an honest human-in-the-loop flag, and optionally a verdict reason-class.¶
The party that constructs Capsules and may create one or more independent Producer Envelopes over a Capsule ID.¶
A COSE_Sign1 object whose attached payload is the raw 32-byte Capsule ID.
It authenticates one signing key's commitment to that identity without
changing the Capsule or its capsule_id.¶
Any party that validates a Capsule from its bytes, without trusting the Producer. Verifier conformance is split into two classes (Section 7).¶
New Capsules compute JSON digests with plain JSON Canonicalization Scheme
(JCS) [RFC8785] and declare canonicalization_id: "jcs". No absent-field
normalization is applied: null, empty arrays, and empty objects participate
when present. JSON floating-point values are forbidden in digest-bearing
material, and integers outside the IEEE-754 safe range MUST be represented as
decimal strings.¶
The withdrawn jcs-n construction of
[I-D.mih-sokolov-scitt-payload-binding] remains only as a vintage
Capsule-ID verification path. It is selected by a format-2 Capsule in which
canonicalization_id is absent. A producer MUST NOT emit jcs-n, and a
verifier MUST reject any explicit canonicalization_id: "jcs-n" declaration.¶
A Producer Envelope is a tagged COSE_Sign1 [RFC9052] object (CBOR tag 18,
[RFC8949]). It signs the Capsule's stable identity, not the Capsule JSON.
Its attached payload MUST be the raw 32 bytes obtained by decoding the
Capsule's 64-character lowercase hexadecimal capsule_id. The payload MUST
NOT be hexadecimal text or a JSON serialization.¶
The protected header map MUST contain exactly these three entries:¶
| COSE label | Value | Meaning |
|---|---|---|
1 (alg) |
-8 | EdDSA using Ed25519. |
3 (content type) |
application/agent-action-capsule-id
|
The attached raw Capsule-ID payload. |
4 (kid) |
raw 32-byte Ed25519 public key | Self-contained verification key and self-attested signer identifier. |
The unprotected header map MUST be empty in a bare Producer Envelope. The
signature MUST be a 64-byte Ed25519 signature over the COSE Sig_structure
with context Signature1, the encoded protected map, an empty external AAD,
and the attached payload.¶
A Capsule MAY have zero, one, or multiple Producer Envelopes. Each envelope
is an independent object and MUST verify independently against the same
Capsule ID. Envelopes are not embedded in the Capsule-ID preimage. Adding,
removing, or replacing an envelope therefore never changes capsule_id.
This document does not mandate a container representation for carrying a
Capsule together with its envelopes.¶
Successful Producer Envelope verification proves that the holder of the
private key corresponding to the protected kid signed the Capsule ID. It
does not prove that this key is authorized for the Capsule's operator,
developer, or action. Key authorization is caller policy and is deliberately
separate from the cryptographic verdict. A verifier MUST return the
authenticated public key so the caller can apply an allow-list, certificate,
DID, SPIFFE, or other authorization policy without changing this wire profile.¶
A bare Producer Envelope is not an [RFC9943] Signed Statement. Its protected
map intentionally contains only the three entries in Section 3.1, whereas an
RFC 9943 Signed Statement additionally requires protected CWT iss and sub
claims. A conforming Transparency Service therefore MUST NOT treat a bare
Producer Envelope as an RFC 9943 Signed Statement.¶
To make a Capsule ID transparent, a registrar creates a distinct RFC 9943
Signed Statement whose attached payload is the same raw 32-byte Capsule ID and
whose content type is application/agent-action-capsule-id. That registration
statement MUST satisfy every RFC 9943 protected-header requirement, including
CWT iss and sub. The returned Receipt binds the registration statement to
the service's append-only log. It does not replace or modify any Producer
Envelope and does not by itself authorize a Producer Envelope key.¶
Receipt format, Merkle-tree proof construction, and proof verification are
SCITT substrate concerns defined by reference to
[I-D.ietf-cose-merkle-tree-proofs] and an applicable receipt profile such as
[I-D.ietf-scitt-receipts-ccf-profile]. Verification is compositional: verify
the Capsule ID, verify each Producer Envelope independently, require the SCITT
registration statement payload to equal that raw Capsule ID, then verify its
Receipt under a trusted Transparency Service key. A verifier MUST NOT report
attestation_mode: "anchored" unless all applicable registration-statement and
Receipt checks succeed.¶
An asynchronously observed consequence, such as a reversal, dispute,
correction, or confirmation, is recorded as a new Capsule with its own
Capsule ID. It MAY carry its own Producer Envelopes. Correlation uses payload
fields such as action_id, decision_id, external_ref, and chain; it does
not mutate the original Capsule. The log remains append-only and the original
identity remains immutable.¶
Seven vocabularies of this profile are registry-governed under a
Specification Required policy ([RFC8126], Section 4.6):
verdict_class, disposition.decision, effect.type,
irreversibility_class, effect_attestation, chain.relation, and
citation_purpose. The
registries and their initial contents are defined in Section 12, kept at
the back of this document per convention.¶
The binding invariant, stated once here and again in Section 12: verifiers MUST treat unregistered values as informational and MUST NOT reject a Capsule for carrying one. Registration governs shared meaning, never acceptance. Every registry check in this profile is performable from the Capsule's own bytes and the registry contents alone.¶
A Capsule is a JSON object: the envelope that is disclosed and digest-committed. Sensitive content (model reasoning, evaluated evidence, raw tool payloads) is not carried in the envelope; it is committed to by digest only. A Capsule also carries Constraint Records — the public verdicts of the deterministic checks that ran against the action; their detail is specified in Section 8.1.¶
| Field | Type | Req | Meaning |
|---|---|---|---|
| spec_version | string | REQUIRED | The profile prose version the Capsule conforms to. The value defined by this profile version is "draft-mih-scitt-agent-action-capsule-04". |
| format_version | string | REQUIRED | The serialization-suite version. New Capsules use "4". Vintage format-2 Capsules remain verifiable only under the compatibility rule below. |
| canonicalization_id | string | REQUIRED for format 4; MUST be absent for format 2 | New Capsules MUST carry exactly "jcs". Explicit "jcs-n", empty, null, non-string, and unknown declarations are invalid. |
| capsule_id | string (64 lowercase hex) | REQUIRED | The derived identifier. For format 4, compute SHA-256 over plain JCS of the Capsule with only capsule_id removed. The canonicalization_id declaration and chain block participate. Verifiers MUST recompute; carried values MUST NOT be trusted. |
| action_id | string | REQUIRED | Stable identifier of the action; unique within one producer ledger. |
| action_type | string | REQUIRED | "fyi" (informational) or "decide" (a disposition was required). |
| operator | string | REQUIRED | The accountable tenant the action was performed for. |
| developer | string | REQUIRED | The agent identity and version that performed the action. |
| timestamp | string | REQUIRED | [RFC3339] UTC with "Z" suffix. |
| epoch_id | string | OPTIONAL | An operator-assigned epoch identifier, stable within one operational configuration of the agent system. Producers SHOULD populate this field and rotate its value — together with an epoch-boundary Capsule (Section 5.2) — when a configuration change that materially alters agent behavior occurs (for example, a model-version swap, a policy-manifest revision, or a significant constraint-schema change). A verifier or ledger consumer scopes a history window to a specific operational configuration by filtering on operator and epoch_id. Absent epoch_id implies a single, unnamed epoch; a producer MUST NOT back-fill epoch_id on Capsules already sealed. |
For a vintage format-2 Capsule, canonicalization_id MUST be absent. Its
Capsule ID is verified by removing capsule_id and chain, applying the
legacy absent-field normalization, then applying JCS and SHA-256. This path is
verification-only. A producer MUST NOT emit a new format-2 Capsule.¶
Monetary and quantity values are subject to the exact-decimal-string requirement in Section 2.¶
A configuration epoch is the contiguous sequence of Capsules produced by one agent configuration — one model version, one policy-manifest version, one runtime variant — before any of those configuration dimensions changes. Epochs exist because a model swap or policy revision is a behavioral discontinuity; without a recorded epoch boundary, pre- and post-change history blend silently and a verifier cannot scope a query to "the current configuration."¶
The epoch_id payload field (Section 5.1) carries the current epoch
identifier. It is committed to capsule_id and is therefore tamper-evident.
Producers that operate across multiple epochs SHOULD populate epoch_id and
rotate its value on every configuration change. Producers that do not
anticipate epoch changes MAY omit it; absent epoch_id implies a single,
unnamed epoch.¶
A producer MUST NOT assign the same epoch_id value across a configuration
boundary. The invariant "all Capsules sharing an operator and epoch_id were
produced under the same configuration" is what makes epoch-scoped history
queries meaningful; violating it makes pre- and post-change records
indistinguishable by epoch_id alone.¶
When an epoch opens, a producer SHOULD emit a single epoch-boundary Capsule before resuming normal action recording. An epoch-boundary Capsule is a regular Capsule (no new statement type) with:¶
action_type: "fyi" (it is an administrative record, not a decided
action);¶
the new epoch_id value — the epoch it opens;¶
chain.relation: "epoch_opens" linking to the last Capsule produced
under the prior epoch (registry-governed, Section 12); and¶
a RECOMMENDED model_attestation block (Section 5.1) recording the
new model and provider, so the transition is commit-addressed and verifiable
from the Capsule's own bytes.¶
An epoch-boundary Capsule MAY additionally carry disposition.verdict_class:
"epoch_boundary" (registry-governed, Section 12) and a reason_digest
committing to a machine-readable record of what changed — at minimum the
prior epoch_id, the new model identity, and the new policy-manifest
version — so that a verifier can distinguish a configuration-change record
from an ordinary fyi action.¶
A verifier scoping a query to a specific epoch filters by operator and
epoch_id. An epoch-boundary Capsule carrying chain.relation: "epoch_opens"
marks the temporal left edge of that epoch; the next epoch-boundary Capsule
whose chain parent lies within this epoch marks its right edge. A verifier
SHOULD report, as an informational finding, any action Capsule whose
epoch_id differs from the prevailing epoch established by the most recent
epoch-boundary Capsule for that operator; such a discrepancy is not a
verification failure (an epoch change mid-stream is not structurally
non-conforming), but it is evidence that a configuration boundary occurred
without a corresponding epoch-boundary Capsule.¶
For format 4, the chain block participates in capsule_id. Changing a
parent identifier or relation after sealing therefore changes the recomputed
identity and invalidates every Producer Envelope over the prior Capsule ID.
Only vintage format-2 verification excludes chain.¶
The Effect Record describes the side effect the action committed. Its
status member takes one of five values:¶
| status | Meaning | Binding requirement |
|---|---|---|
| planned | Intended, not dispatched. | request_digest and response_digest MUST be absent. |
| dispatched | Sent; result not observed. | request_digest SHOULD be present; response_digest MUST be absent. |
| confirmed | Result observed and bound. | response_digest MUST be present and MUST be a JSON digest (Section 2) of the actual response. |
| failed | Attempted; runtime reported failure (state known). | response_digest, when present, digests the failure response. |
| reverted | A committed effect was undone. | Correlated via external_ref / decision_id. |
The confirmed-effect invariant: a producer MUST NOT emit
status: "confirmed" without a response_digest over the actually
observed response. A verifier MUST treat confirmed with a missing
response_digest as a verification failure. This is the byte-level
mechanism behind the may/did distinction: "confirmed" is an observed
result, never a promise.¶
The Effect Record also carries the logical type (registry-governed,
Section 12), an optional external_ref join key for later outcomes, and an
irreversibility_class — an ordered consequence enumeration (two_way,
one_way_recoverable, one_way_consequential, one_way_terminal;
registry-governed, Section 12).¶
The Effect Record additionally carries effect_attestation: WHO vouches
for the effect's execution — the evidence grade of the effect claim. The
vocabulary is registry-governed (Section 12; Specification Required), seeded
with two values:¶
| effect_attestation | Meaning |
|---|---|
| gate_executed | The commit transited the gate; the engine observed the effect boundary directly. |
| runtime_claimed | The gate issued a verdict only; the executing runtime asserted completion; the capsule records that claim, not an observation. |
Validity is checked against the assurance effect_mode (Section 5.4):¶
| effect_mode | effect_attestation |
|---|---|
| confirmed | REQUIRED (states WHO confirmed) |
| dispatched_unconfirmed | REQUIRED |
| not_applicable | MUST be absent — nothing executed, there is no claim to grade |
The planned carve: effect.status: "planned" asserts no execution, so
effect_attestation MUST be absent — there is nothing to grade, and a
phantom grade would poison grade-based queries. It becomes REQUIRED the
moment dispatch occurs.¶
The matrix is total over the effect.status values of Section 5.3. An
effect.status of failed (the effect was dispatched and the runtime
reported a failure; state known) derives effect_mode:
"dispatched_unconfirmed" — the effect was dispatched and its result, though
a failure, was not gate-confirmed; therefore effect_attestation is REQUIRED.
reverted (a previously-committed effect was undone) likewise derives
effect_mode: "dispatched_unconfirmed" and REQUIRES effect_attestation; the
underlying committed effect it reverses is correlated separately via
external_ref / decision_id (the Effect Record fields, Section 5.3), not
by a distinct effect_mode. So
every effect.status other than planned (carved above) and the
no-effect case (not_applicable) requires effect_attestation.¶
Consumers MUST treat an unregistered or unrecognized effect_attestation
value as no stronger than runtime_claimed; unknown values are
informational, never a verification failure, and unknown never grades up.
The grade is digest-committed in the Capsule payload and is available to
any payload-bearing verifier, distinguishing gate-observed execution from
runtime-claimed execution. It is not copied into a Producer Envelope header.¶
References to external authorization records carried in the Effect Record (for example, permit receipts per [I-D.munoz-scitt-permit-profile], or machine mandates) are typed digest references per [I-D.mih-sokolov-scitt-payload-binding]'s Typed Digest References section, with artifact types drawn from the CPB Artifact Type registry. Cross-profile comparability of digest values (comparable only under compatible declared digest contexts; otherwise indeterminate/deny, never equal-looking-hex) follows that document's Cross-Profile Comparability subsection.¶
NOTE: docs/interop/aac-aep-scitt-digest-binding-vector.json pins a
machine-checkable positive/negative demonstration of this Cross-Profile
Comparability rule across AAC, AEP, and SCITT under the profile label
urn:action-state:aac-aep-scitt:digest-binding:2026-07-02.¶
This profile's own chain.parent_capsule_id, reason_digest,
evidence_digest, and external_ref fields are a distinct concept from
the typed digest reference above: they are bare intra-profile digests and
join keys, either a current JSON digest or an opaque correlation string, not
{type, digest_alg, digest} objects citing an external artifact by
registered artifact type. They MUST NOT be interpreted as CPB typed digest
references. Only the external-authorization references described in this
paragraph use the CPB typed-reference mechanism.¶
Every Capsule carries an assurance object stating, as
independently-rederivable claims: attestation_mode ("self_attested" or
"anchored"), effect_mode ("not_applicable", "dispatched_unconfirmed", or
"confirmed"), and ledger_mode ("standalone", "chained", or "anchored").
ledger_mode records the custody tier of the record: "standalone" is a
lone Capsule (no chain linkage); "chained" is a Capsule whose hash-chain
linkage to a predecessor is present and intact; "anchored" is a chained
Capsule whose chain root has additionally been committed to an independent
transparency log. A verifier rederives ledger_mode from the bytes it can
check — "standalone" versus "chained" from the presence and integrity of
the hash-chain linkage, and "anchored" only after it verifies an inclusion
proof against a trusted log key — and the three tiers are ordered
standalone < chained < anchored for overclaim detection. A producer MUST
NOT record an assurance mode it did not achieve; a verifier rederives each
mode from the evidence present and reports any overclaim.¶
A Capsule's evidentiary weight along the counterparty dimension — how
much of a counterparty's own attestation is structurally present in this
record — is a fourth, orthogonal claim: assurance.cross_party_rung. It
is a new axis, not a new value folded into attestation_mode, for the
same reason Section 5.5.2 already gives for keeping verdict_class
and effect_mode separate: attestation_mode answers "has this record
been committed to an independent transparency log" (log custody);
cross_party_rung answers "how much of the counterparty's own signed
evidence is bound into this record" (exchange evidence). These are
independent facts a producer can hold in any combination — a
self_attested record can still be full_bilateral (both parties signed,
neither side anchored yet), and an anchored record can still stand on
unilateral_fallback evidence alone (a solo attestation that was
independently anchored). Folding a countersigned value into
attestation_mode would collapse these two facts into one claim and make
that combination inexpressible, so this profile keeps them orthogonal.¶
cross_party_rung takes one of three values, ordered
unilateral_fallback < acknowledged_receipt < full_bilateral for
overclaim detection — the same never-grades-up discipline
Section 5.4 already applies to attestation_mode, effect_mode, and
ledger_mode:¶
| cross_party_rung | Meaning |
|---|---|
| unilateral_fallback | Only the initiator's own signed half is present; no counterparty evidence, or the counterparty was unreachable or its half did not verify. |
| acknowledged_receipt | A counterparty reference and correlator are present and well-formed: the counterparty cryptographically acknowledged receipt, but the referenced half carries no substantive co-signed result. |
| full_bilateral | A counterparty reference and correlator are present and well-formed, and the referenced half is marked as carrying a substantive co-signed result — both parties' evidence is bound to the same exchange. |
cross_party_rung is REQUIRED when a cross_party evidence block (below)
is present, and both are OPTIONAL on a Capsule with no cross-party
exchange. A producer MUST NOT claim a cross_party_rung its evidence does
not support. A Class-1 verifier independently rederives the highest rung
the cross_party block supports and reports any claim above the derived
rung as an assurance_overclaim (Section 6), downgrading the
reported derived rung to the value the evidence actually supports — the
same treatment Section 6 already gives an overclaimed
attestation_mode or ledger_mode.¶
A Capsule that participates in a cross-party exchange carries an OPTIONAL
top-level cross_party block:¶
initiator_ref (REQUIRED when the block is present): a JSON digest
(Section 2) of the initiator's own signed half. A bare
intra-profile digest, not a CPB typed digest reference (Section 5.3).¶
counterparty_ref (OPTIONAL): a JSON digest of the counterparty's
signed half. Its absence means no usable counterparty evidence was
obtained — the counterparty was unreachable, or its half did not verify
at the layer that checked it.¶
correlator (REQUIRED when counterparty_ref is present): an opaque
profile-native correlation string joining initiator_ref and
counterparty_ref to the same exchange — the same kind of "opaque
correlation string" primitive external_ref already uses (Section 5.3),
not a CPB reference.¶
substantive (OPTIONAL boolean, meaningful only when counterparty_ref
is present): true only when the counterparty's referenced half carries a
substantively co-signed result rather than a bare receipt of the
initiator's half.¶
A verifier derives cross_party_rung from this block's own bytes alone,
never by dereferencing the digests it cites: unilateral_fallback when
counterparty_ref is absent or malformed; acknowledged_receipt when
counterparty_ref and correlator are both present and well-formed but
substantive is absent or false; full_bilateral when
counterparty_ref and correlator are both present and well-formed and
substantive is true. This is a structural check, the same kind
Section 5.4 already uses to derive "chained" from the mere presence of a
well-formed chain block — it does not verify the counterparty's
underlying signature itself, which is a substrate concern by reference
(Section 6), mirroring how this layer never derives anchored.
The two-party wire encoding this rung summarizes — the initiator and
counterparty attestation halves, their signatures, and the handshake that
produces them — is the companion
[I-D.mih-agent-bilateral-attestation]'s concern, not this profile's;
this profile carries only the rung claim and the minimal correlation
evidence needed to rederive it honestly.¶
A Capsule's disposition block records how the decision was disposed:¶
decision (REQUIRED): "accept", "reject", "needs_input", or "deferred"
(registry-governed, Section 12).¶
approver (REQUIRED): a closed enum, exactly "human", "policy", or
"counterparty". The value domain is fixed by this specification (not
registry-governed); an unknown approver value is not a conforming
Capsule. Unlike the registry-governed vocabularies of this document
(Section 12), approver stays a closed three-member enum after this
addition — never a registry an implementation is expected to extend by
registration.¶
human_disposed (REQUIRED, boolean): the honest in-the-loop flag —
true ONLY when a human actually acted. A policy auto-approval is false.
human_disposed: true REQUIRES approver: "human"; a producer MUST
NOT claim a human disposed what a policy did.¶
authority (OPTIONAL): an opaque reference to the authority under
which a non-human disposition acted. A conforming Capsule carries at
most the reference, never the authority's internal structure.¶
verdict_class (OPTIONAL): the terminal-verdict reason-class
(Section 5.5.1). It is RECOMMENDED for any non-executed verdict,
where it carries the terminal reason; it is legitimately absent for a
clean executed verdict (which has no reason-class, mirroring an absent
reason_digest).¶
reason_digest (OPTIONAL): a JSON digest (Section 2) of a structured, private reason
object — machine-readable members such as the constraint identifier,
the threshold, and the observed value; never free prose — so two
engines attesting the same refusal produce the same digest. The member
is absent (not a digest of an empty object) when a verdict has no
reason, such as a clean "executed".¶
expiry_policy (OPTIONAL; deferral dispositions only): a digested
{ttl_seconds, on_expiry} object — ttl_seconds is an integer count
of seconds, never a duration string, and on_expiry is "expired" or
"escalated". ttl_seconds is evaluated against the deferral Capsule's
registration time — the timestamp field inside the digest commitment
— not the Transparency Service receipt time, and not a consumer's
local wall clock; a named clock basis is what makes the expiry
computation deterministically reproducible, so any verifier derives the
same elapsed-time result from the record's own bytes. The deferral's
frozen summary is a
digest-committed, content-side layer written once at deferral time; it
MUST NOT be regenerated.¶
approver: "counterparty" (see Section 5.4.1) records that a
counterparty to a cross-party exchange, rather than this operator's own
human or policy, disposed the decision. The honesty invariant above is
unaffected: human_disposed: true still REQUIRES approver: "human",
so a counterparty disposition is never claimed as human-in-the-loop.¶
verdict_class records WHY the action terminated as it did. The seeded
vocabulary (registry-governed, Section 12; unregistered values are
informational to a verifier, never a rejection):¶
| verdict_class | Meaning |
|---|---|
| executed | The action ran. |
| blocked | A blocking constraint stopped it before dispatch. |
| hitl_dispatched | Routed to a human operator; awaiting resolution. |
| denied | An operator or policy refused it before dispatch. |
| timeout | The decision timed out (see the orthogonality rule). |
| errored | The action ran and threw; final state unknown. |
| engine_failure | The engine could not evaluate the action. |
| deferred | A human elected to postpone the decision; open item. |
| needs_decision | Evaluation complete; decision required, not yet routed to a decider; open item. |
| expired | TTL policy on the deferral elapsed; terminal unless superseded by escalation. |
| escalated | Expiry or policy routed the item to a higher authority; open item at the new authority. |
| resolved | A terminal decision Capsule closed the chain without executing — the non-executing closure only (see the pairing rule, Section 5.5.2). |
hitl_dispatched and deferred are sequential states, not synonyms:
hitl_dispatched means sent to a decider and awaiting response;
deferred means a decider responded "later".¶
verdict_class (why the verdict) and assurance.effect_mode (what is
known about the effect) are independent axes and MUST NOT be folded into
one another:¶
The pre/post-dispatch distinction lives in effect_mode, not in the
class. A timeout before dispatch is verdict_class: "timeout" with
effect_mode: "not_applicable"; a timeout after dispatch is
verdict_class: "timeout" with effect_mode: "dispatched_unconfirmed".
One timeout value covers both.¶
errored pairs with effect_mode: "dispatched_unconfirmed" — the
effect was dispatched and may have left a partial side effect.
not_applicable would falsely assert nothing happened, which is the
inverse of attesting an execution that did not occur and equally
non-conforming.¶
A class that by its kind never dispatches (blocked,
hitl_dispatched, denied, engine_failure, deferred,
needs_decision, expired, escalated, resolved) REQUIRES the
derived effect_mode to be "not_applicable". A verifier reports any
other derived mode as an error: an effect attempt contradicts a
verdict that claims it never executed.¶
The pairing rule: resolved is exclusively the NON-executing closure
(decline, waive, recorded-elsewhere) — it pairs with effect_mode:
"not_applicable" and an absent effect_attestation. An EXECUTING
closure is encoded as verdict_class: "executed" chained
supersedes to the deferral (Section 5.5.4) — one valid encoding of
"closed with effect", never two.¶
The effect status "failed" (ran and returned a clean failure, state
known) is distinct from verdict_class: "errored" (ran and threw,
state unknown). "failed" is an effect status, never a reason-class.¶
A conforming producer MUST record a Capsule for every verdict, whatever
its disposition. This requirement is universal over the verdict_class
vocabulary — the IANA registry of this document (Section 12) — and
applies to every value later admitted by registration; it is
deliberately not stated as an enumerated list, which would go stale the
moment Specification Required admits a new value. A refusal or block with
no Capsule is invisible to an auditor; a blocked or denied Capsule is
auditor-grade evidence that the gate worked: the affirmative,
digest-committed record that the constraint or policy fired and the
action did not proceed. Recording only successes makes the evidence trail
survivorship-biased and the refusal path unverifiable.¶
Every Capsule that references a prior Capsule carries a digested chain
block: {parent_capsule_id, relation}. The relation vocabulary is
registry-governed (Section 12; Specification Required), seeded with one
value:¶
| relation | Meaning |
|---|---|
| confirms | Non-terminal: this Capsule observes or records the outcome of the parent; the parent's open state remains. |
| supersedes | Terminal transition over the parent — resolution, expiry, escalation close or replace the parent's open state. |
| epoch_opens | Non-terminal: this Capsule opens a new operational epoch. The chain parent is the last Capsule produced under the prior epoch. The opening Capsule carries the new epoch_id (Section 5.2.2); the prior epoch's last Capsule is the parent. |
Single-parent is intentional: a Capsule chains to exactly one parent.¶
Human-in-the-loop resolution is the supersedes relation: a
hitl_dispatched Capsule is sealed at dispatch time and is never
mutated. When the decision is later resolved, that resolution is a
second, linked Capsule carrying its own disposition and chaining to the
dispatch Capsule with relation: "supersedes". The dispatch Capsule
stays hitl_dispatched forever; resolution state lives only on the
resolution Capsule, preserving the append-only model.¶
Concurrent-supersedes rule: the ledger is append-only and totally
ordered; the earliest capsule in ledger order with relation=supersedes
over a given parent is authoritative; any later supersedes over the same
parent is structurally valid but MUST surface as a verification finding.¶
Open-items predicate: an item is open when its Capsule's
verdict_class is one of deferred, needs_decision,
hitl_dispatched, escalated, or blocked, and no Capsule in the
store carries chain.parent_capsule_id equal to its capsule_id with
relation: "supersedes".¶
chain presupposes the cited Capsule is this producer's own: it is
scoped to same-custody-stream, single-parent state transitions
(Section 5.5.4). It has no shape for citing a record outside that stream —
a different producer's Capsule, or any other artifact this Capsule's
action was performed on or in response to. A Capsule MAY carry a
digested references array for exactly that case; absent or empty
means the Capsule makes no such citation. Like the rest of the payload,
references participates in the capsule_id digest (Section 5.1):
citing a record is itself a claim this Capsule's signature covers.¶
Boundary rule. chain is exclusively the producer's own same-stream
parent and is the only field Section 5.4's ledger_mode derivation
reads. references is exclusively for everything else. A references
entry MUST NOT name the same target as chain.parent_capsule_id — a
producer citing its own same-stream parent states that once, in
chain, never redundantly in references.¶
Shape. Each references entry's identity is a CPB typed digest
reference [I-D.mih-sokolov-scitt-payload-binding]: {type, digest_alg,
digest}, the same mechanism this profile already uses for the
external-authorization references of the Effect Record (Section 5.3).
type names an artifact type per the CPB Artifact Type registry; this
document defines the references entry shape, not an exhaustive list
of what may be cited.¶
A reference MAY additionally carry log_coordinates, an object
{log_id, leaf_index, inclusion_proof}, present as a unit when the
cited record has been registered to an append-only log a verifier can
consult. log_coordinates is an upgrade, not a second identity: it
proves the exact referenced bytes were found at the stated log
position, and its presence or absence never changes what type +
digest_alg + digest already identify. Producer-local log
checkpointing is future scope at the CPB binding layer, not this
document (Section 11); until that mechanism is specified, a Class 1
verifier treats a present log_coordinates member as structurally
recorded and MUST NOT report it as independently verified.¶
Citation purpose. A references entry MAY carry citation_purpose,
a registry-governed (Specification Required, Section 12) string stating
why this Capsule cites the target. citation_purpose is a distinct
vocabulary from CPB's own purpose field on a typed digest reference:
CPB's purpose selects among an artifact type's registered digest
contexts, and citation_purpose is this profile's own, separately-named
field for the citing relationship, never a repurposing of CPB's field.
The seeded vocabulary:¶
| citation_purpose | Meaning |
|---|---|
| acted_on | This Capsule's action targeted, consumed, or was performed against the cited record's declared content — a stream boundary, not a custody claim: the cited record may belong to a different producer or stream entirely, and citing it asserts only that this action is about that content, never that the citing producer holds or continues its custody. |
| responds_to | This Capsule addresses or answers the cited record without a same-stream chain relationship to it — the cited record is not this Capsule's chain.parent_capsule_id and MAY be a different producer's record or otherwise outside this producer's own stream. |
Designated-expert guidance: both seeded values name a cross-stream
citation intent that chain.relation cannot express because
chain.relation is scoped to same-stream transitions (Section 5.5.4). A
producer whose citation is a same-stream state transition over its own
parent uses chain instead and never mints a references entry for it
(the boundary rule above). Additional citation_purpose values are
expected future registrations, each admitted once its semantics are
pinned in a publicly available specification, per this document's
Specification Required policy (Section 12).¶
Relation to chain.relation's confirms value in deployed
implementations. A cross-stream citation — for example, a denial
Capsule addressing a prior record that is not its own chain parent — is
not a same-stream state transition and so is not a chain.relation
value under this profile; chain.relation registers no value for it,
and none is added by this revision. Such a citation is a references
entry with citation_purpose: "responds_to" (or "acted_on", if it is
the affirmative case). An implementation using chain with a
confirms-shaped relation for a citation that is not the same-stream
parent is not using chain as this document defines it; the compatible
migration is a references entry with the appropriate
citation_purpose, not a fourth chain.relation value.¶
Capsule verification and Producer Envelope verification are independent. A verifier can validate a Capsule with no envelope, and can validate any number of envelopes against a Capsule ID without changing the Capsule result.¶
For each Producer Envelope, a verifier MUST:¶
validate the exact tag, protected map, empty unprotected map, attached payload, and signature sizes in Section 3.1;¶
require the attached payload to equal the raw 32 bytes of the Capsule ID;¶
verify the Ed25519 signature under the public key carried in kid; and¶
return that authenticated public key separately from any caller-defined authorization decision.¶
Malformed or unverifiable envelopes MUST produce structured failures and MUST NOT cause the verifier to throw or panic. One invalid envelope does not erase the validity of another independent envelope over the same Capsule ID. Receipt verification is a separate substrate step performed by reference to [RFC9943] and [I-D.ietf-cose-merkle-tree-proofs].¶
The agent-profile checks below are normative here and constitute Class 1
verification (Section 7): every check is performable from the
Capsule JSON, the registry contents
(Section 4), and — for the chain checks — the producer's store of
Capsules; no other input is needed. A verifier MUST return a structured
result, never throw; a single ok boolean gates trust in every other
reported field; findings are reported in a fixed order.¶
Structural: REQUIRED fields present and typed; no floating-point
values in digest-bearing fields; format 4 requires exactly
canonicalization_id: "jcs"; format 2 requires the field to be absent;
unknown formats and all other declarations fail closed.¶
Identity: for format 4, remove only capsule_id and compute SHA-256 over
plain JCS. For vintage format 2, remove capsule_id and chain, apply
absent-field normalization, then JCS and SHA-256. Compare the result with
the carried capsule_id.¶
Confirmed-effect binding: effect.status: "confirmed" without a
well-formed response_digest is a failure (Section 5.3).¶
Verdict/effect orthogonality: a never-dispatching verdict_class
with a derived effect_mode other than "not_applicable" is a
failure (Section 5.5.2); resolved is in the never-dispatch set
per the pairing rule.¶
Effect-attestation matrix: effect_attestation missing where the
matrix REQUIRES it, or present where it MUST be absent — including
the planned carve — is a failure (Section 5.3).¶
Chain semantics (store-level): a missing chain parent is a failure;
concurrent supersedes surface as findings per Section 5.5.4. A
references entry (Section 5.5.5) is a different claim: it is informational
cross-stream correlation, never a chain-integrity input, and a
verifier MUST NOT treat a references entry naming an unresolvable
or absent target as a chain-semantics failure — only a references
entry that duplicates chain.parent_capsule_id is a failure, per the
boundary rule of Section 5.5.5.¶
Assurance reconciliation: rederive the assurance modes from evidence actually verified; report overclaims.¶
Unknown registry values (verdict_class, decision,
effect.type, irreversibility_class, effect_attestation,
chain.relation, citation_purpose): report as informational
findings; MUST NOT reject (Section 12). An unknown effect_attestation
is additionally graded no stronger than runtime_claimed (Section 5.3).¶
Disposition honesty is structurally guaranteed, not a live check above.
The honesty invariant — human_disposed: true REQUIRES approver:
"human" (Section 5.5) — is enforced when the disposition is
constructed: the typed disposition carrier rejects human_disposed:
true paired with any non-human approver, so a violating Capsule
cannot be formed or signed at all. A Class 1 verifier
therefore does not re-assert it in the enumeration above; like
parse- and type-level malformations that a typed record cannot
represent, a dishonest disposition is an unrepresentable state rather
than a runtime failure mode. A verifier consuming arbitrary bytes not
produced by a conforming constructor SHOULD nonetheless assert the
invariant defensively against hand-crafted input. The
closed approver enum (Section 5.5) is likewise structural: an
approver value outside {human, policy} is non-conforming by
construction and so is absent from the unknown-registry-value reporting
of check 8.¶
NOTE (Class 1 test vector, effect-attestation matrix, check 5): a Capsule
carrying effect.status: "failed" derives effect_mode:
"dispatched_unconfirmed" (Section 5.3); the matrix therefore REQUIRES
effect_attestation. A conforming verifier MUST report a check-5 failure
for such a Capsule when effect_attestation is absent, and MUST NOT treat
the failed status as exempt (only planned is carved, and only
not_applicable is the no-effect case). The same expectation holds for
effect.status: "reverted", which likewise derives
dispatched_unconfirmed. This vector exists to demonstrate the matrix is
total over effect.status: the runtime reporting a failure is still a
dispatch, and a dispatch that escapes attestation is the precise condition
check 5 exists to catch.¶
A verifier MUST NOT consult a model, a clock-dependent heuristic, or
network state to decide ok for the checks above. Manifest-dependent
verification is Class 2 (Section 8.2).¶
This profile defines two verifier conformance classes. Producer conformance is a single class and is unchanged by this split: a conforming producer emits the same Capsules regardless of which verifier class consumes them.¶
Verifies the Capsule payload WITHOUT any constraint manifest: the structural and identity checks, the registry vocabularies, the digest recomputations, and the validity matrices (confirmed-effect binding, verdict/effect orthogonality, effect-attestation, chain semantics). The complete Class 1 check set is Section 6. Producer Envelope and Receipt results are reported independently and do not alter payload Class 1.¶
A Class 1 verifier that additionally performs manifest-aware verification (Section 8.2): constraint evidence-schema checks and manifest-sourced thresholds. Class 2 conformance presupposes access to the producer's constraint manifest and the private evidence its Constraint Records bind; absent those inputs, a Class 2 verifier reports Class 1 results unchanged.¶
The producer's constraint manifest — the private definition of each constraint's predicate, evidence schema, and thresholds — is not carried in the Capsule. The material in this section depends on it: the detail of Constraint Records and the Class 2 checks. Manifest discovery and authentication are out of scope for this profile; they are expected to be handled via out-of-band tenant configuration or a future discovery mechanism.¶
A Constraint Record is the public verdict of one deterministic check that
ran against the action. It carries only sanitized categories — an id,
optional check_type and method labels, a result of "pass" / "fail" /
"n/a", severity, a blocking flag recording whether the check actually
gated this decision, and an optional evidence_digest (a JSON digest,
Section 2) binding the verdict to the private evidence the check evaluated. The
content a check evaluated MUST NOT appear in the public record; it is
bound by digest only. The check's predicate, evidence schema, and
thresholds live in the producer's manifest.¶
Every recorded result MUST be the output of a deterministic predicate
over disclosed or digest-committed evidence. The live decision path MUST
NOT re-prompt a model to make a check pass, and a verifier MUST NOT
re-prompt a model to "re-check" one: re-running a non-deterministic check
is not verification.¶
Constraint id, check_type, and method values are lowercase
snake_case categories. New values follow the namespacing convention of
Section 9.1.¶
The checks below are manifest-aware: they require the producer's constraint manifest and the private evidence a Constraint Record binds by digest. A Class 2 verifier performs them in addition to the complete Class 1 set (Section 6); their results never weaken a Class 1 result — they extend it.¶
Constraint evidence-schema check: for each Constraint Record
(Section 8.1) carrying an evidence_digest, confirm the bound
evidence conforms to the manifest's evidence schema for that
constraint id and that the recomputed digest matches; a mismatch is
a failure.¶
Threshold checks: confirm that manifest-sourced thresholds were applied as the manifest states.¶
All Capsule extension points are in the Capsule JSON. The Producer Envelope protected map is exact and closed by Section 3.1. An extra protected entry is a profile failure, not an extension mechanism. New envelope metadata requires a future format version or a separate carrying structure.¶
Three vocabularies are deliberately not registry-governed — constraint
id/check_type, compliance.framework_tags, and
assurance.sources[].kind — because their value space is producer-local
by nature. Bare names (no namespace separator) are reserved for the
values seeded in this document; any party introducing a new value MUST
namespace it with a URI or reverse-DNS prefix (for example,
com.example.margin_floor). A bare, unseeded name is non-conforming for
a producer; a verifier still treats it as informational.¶
The base confidentiality posture of this profile is whole-envelope: a producer discloses a Capsule by sharing its full payload, or withholds it entirely. Sensitive content not carried in the envelope leaves no on-wire indicator of its existence. This whole-envelope posture is sufficient for the common case where the unit of disclosure is the Capsule as a whole.¶
For cases in which a producer must reveal a subset of payload fields to a verifier while concealing both the values and the existence of unrevealed fields, a per-field selective-disclosure mechanism is needed. This profile reserves an extension point in the Capsule payload for such a mechanism. The intended field-level technique follows the SD-JWT selective-disclosure model [RFC9901] — salted-hash commitments over JCS-canonicalized arrays — because the Capsule payload is JSON; it is written to stay aligned with SPICE's SD-CWT [I-D.ietf-spice-sd-cwt] (the CBOR sibling) for SCITT-ecosystem consistency.¶
The complete normative profile of this mechanism — including the commitment encoding, disclosure syntax, and verifier checks — is defined in the companion Internet-Draft [I-D.mih-scitt-cpb-selective-disclosure]. That companion is a CPB payload-class document; the mechanism is payload-class-generic. This profile (AAC) retains only the eligibility-policy annex: the declaration of which AAC payload fields are eligible for selective disclosure and which are non-eligible because this profile's own verifier requires their values in clear.¶
Implementations of this profile version MUST NOT generate or interpret selective-disclosure payload structures unless they additionally implement [I-D.mih-scitt-cpb-selective-disclosure]: the extension point is defined only in that companion, and no conformance claim or verification behavior is defined for it in this document.¶
The companion Internet-Draft [I-D.mih-agent-bilateral-attestation] defines a bilateral attestation extension in which two parties independently seal Capsules over a shared action digest, each holding proof of the other's commitment. The extension reuses this profile's disposition vocabulary (executed, blocked, denied, timeout, errored, deferred, expired, escalated) and anchors both seals to a conforming SCITT Transparency Service, so a third party trusting neither signatory can verify the record end-to-end. Statement-type and verdict-class values reserved in this document for that extension are governed by the registries in Section 12.¶
The companion Internet-Draft [I-D.mih-scitt-cpb-selective-disclosure] normatively profiles the selective-disclosure extension point reserved in Section 9.2, specifying the per-field commitment structure, disclosure syntax, eligible fields, and verifier checks, aligned with [I-D.ietf-spice-sd-cwt].¶
Every registry requested below governs a vocabulary that lives entirely in the Capsule JSON. A SCITT-generic Transparency Service does not need to parse those values because registration, inclusion, and Receipt issuance operate on the separate SCITT registration statement. The media-type registrations are addressed separately in Section 12.3. This profile requests no new COSE header parameter or CWT claim registry; the new registries here are payload vocabularies only.¶
IANA is requested to create a new registry group, "Agent Action Capsule Parameters", containing the seven registries below. The registration policy for each is Specification Required ([RFC8126], Section 4.6).¶
Specification Required is chosen deliberately. The threat it answers is a vocabulary value whose meaning is defined only inside a closed product — two verifiers would then disagree on what the value means, and the interoperable, falsifiable-from-the-record property this profile depends on would erode. The mitigation is the policy's publicly-available-spec requirement: a value enters the shared vocabulary only once its semantics are pinned in a specification any implementer can read. Accordingly, for each registry the designated expert approves a registration when (1) the citing specification defines the value's semantics precisely enough that two independent implementations would apply it identically — for verdict_class, including its dispatch consequence and its effect_mode pairing under Section 5.5.2; (2) the value's meaning is not already expressible by an existing registered value; and (3) the citing specification is publicly available.¶
Binding invariant for all seven registries: verifiers MUST treat unregistered values as informational and MUST NOT reject a Capsule for carrying one. Registration governs shared meaning, never acceptance.¶
Initial contents are the seeded values of this document, verbatim:¶
"verdict_class" registry (Section 5.5.1): executed, blocked,
hitl_dispatched, denied, timeout, errored, engine_failure, deferred,
needs_decision, expired, escalated, resolved, epoch_boundary.
The deferred token's semantics are OWNED by this registry; the
entry of the same spelling in the "disposition.decision" registry is
a cross-reference to it. The epoch_boundary token denotes an
administrative Capsule (action_type: "fyi") that marks a
configuration-epoch transition (Section 5.2.2); it REQUIRES
effect_mode: "not_applicable" (no effect is dispatched by an
administrative epoch record).¶
"disposition.decision" registry (Section 5.5): accept, reject,
needs_input, deferred. The deferred entry is a cross-reference to
the "verdict_class" registry, which owns the token's semantics.¶
"effect.type" registry (Section 5.3): write_order, send_payment.¶
"irreversibility_class" registry (Section 5.3; ordered by ascending consequence — a registration states its position): two_way, one_way_recoverable, one_way_consequential, one_way_terminal.¶
"effect_attestation" registry (Section 5.3): gate_executed,
runtime_claimed. The registry definition carries the grade-floor
invariant of Section 5.3 — an unregistered or unrecognized value is
graded no stronger than runtime_claimed; unknown never grades up —
and the planned carve of Section 5.3: with effect.status: "planned"
the member MUST be absent, and it becomes REQUIRED the moment
dispatch occurs. Designated-expert guidance: plausible future
registrations exist and are deliberately not seeded — for example,
independent sensor confirmation of a claimed effect, or hardware- or
TEE-anchored execution; a registration states where its grade sits
relative to the seeded values.¶
"chain.relation" registry (Section 5.5.4): confirms, supersedes, epoch_opens.
Designated-expert guidance: supersedes is the single terminal
relation; confirms and epoch_opens are non-terminal relations, with
epoch_opens reserved for configuration-epoch boundaries
(Section 5.2.2). Additional non-terminal
relations (for example, deposit-toward-open and effort-toward-open
relations, or amends / contradicts) are expected future registrations,
each admitted once its semantics and any verifier consequence are
pinned in a publicly available specification.¶
"citation_purpose" registry (Section 5.5.5): acted_on, responds_to.
This registry is distinct from, and never a repurposing of, CPB's own
purpose field on a typed digest reference
([I-D.mih-sokolov-scitt-payload-binding]), which selects among an
artifact type's registered digest contexts and is orthogonal to any
role a companion profile assigns a digest within a cross-document
citation. Designated-expert guidance: both seeded values name a
citation whose target is outside the citing Capsule's own chain — a
different producer or a different stream (Section 5.5.5); a citation to
the producer's own same-stream chain parent is never expressed
here. Additional values are expected future registrations, each
admitted once its semantics are pinned in a publicly available
specification.¶
Interim registry of record: until this document is published as an RFC,
the registry of record is the REGISTRY.md file of the source
specification repository, seeded with the same initial contents and the
same policy; on publication the IANA registries become the registry of
record. Change controller: Action State Group, Inc. (interim); the IETF
on publication.¶
Attestation/signature algorithms: this profile defines no algorithm registry; algorithm identifiers are those of the existing IANA "COSE Algorithms" registry ([RFC9053]).¶
Constraint id/check_type, compliance.framework_tags, and
assurance.sources[].kind: no registry; governed by the namespacing
convention of Section 9.1.¶
Producer Envelopes use only existing COSE header labels alg, content
type, and kid. This document requests no new COSE header or CWT claim.¶
IANA is requested to register the Capsule JSON media type and the raw
Capsule-ID payload media type in the "Media Types" registry per the templates
below ([RFC6838]). The JSON representation uses the +json
structured-syntax suffix of [RFC8259]. The raw identity payload has no
structured-syntax suffix.¶
Agent Action Capsule media type:¶
Type name: application¶
Subtype name: agent-action-capsule+json¶
Required parameters: N/A¶
Optional parameters: N/A¶
Encoding considerations: binary; the representation is JSON ([RFC8259]) as defined in this document.¶
Security considerations: see Section 13 of this document.¶
Interoperability considerations: see this document.¶
Published specification: this document (and its successors).¶
Applications that use this media type: producers, ledgers, transports, and verifiers recording and verifying AI agent actions.¶
Fragment identifier considerations: as for application/json
([RFC8259]) per the +json suffix ([RFC6839]).¶
Additional information: Deprecated alias names: N/A. Magic number(s): N/A. File extension(s): N/A. Macintosh file type code(s): N/A.¶
Person & email address to contact for further information: the author of this document.¶
Intended usage: COMMON¶
Restrictions on usage: N/A¶
Author: see the Authors' Addresses section of this document.¶
Change controller: Action State Group, Inc. (interim); the IETF on publication.¶
Provisional registration: yes (pending publication of this document).¶
Agent Action Capsule ID media type:¶
Type name: application¶
Subtype name: agent-action-capsule-id¶
Required parameters: N/A¶
Optional parameters: N/A¶
Encoding considerations: binary; exactly 32 octets containing the raw SHA-256 Capsule ID represented in Capsule JSON as 64 lowercase hexadecimal characters.¶
Security considerations: see Section 13 of this document.¶
Interoperability considerations: see this document.¶
Published specification: this document (and its successors).¶
Applications that use this media type: COSE Producer Envelopes and SCITT Transparency Services registering Capsule identities.¶
Fragment identifier considerations: N/A.¶
Additional information: Deprecated alias names: N/A. Magic number(s): N/A. File extension(s): N/A. Macintosh file type code(s): N/A.¶
Person & email address to contact for further information: the author of this document.¶
Intended usage: COMMON¶
Restrictions on usage: N/A¶
Author: see the Authors' Addresses section of this document.¶
Change controller: Action State Group, Inc. (interim); the IETF on publication.¶
Provisional registration: yes (pending publication of this document).¶
The tamper-evidence-versus-runtime-honesty boundary — that the envelope signature and registration Receipt attest record bytes and their timing, not the recording runtime's honesty at the moment of recording — is given in [I-D.mih-sokolov-scitt-payload-binding]'s Security Considerations (Tamper Evidence and Runtime Honesty). This profile inherits that boundary; the following extends it to the confirmed-effect binding.¶
Confirmed means observed-and-bound, not world-state. A confirmed
effect proves the producer bound the bytes of an observed response, not
that the external world reached the claimed state. The same boundary
extends one hop upstream: binding an observed response proves the producer
observed those bytes, not that the responding system was authentic or that
the channel was on-path-intact. An attacker who substitutes or forges the
response — a false success delivered on-path — induces an honest
confirmed Capsule for an effect that did not land; this profile does not
mitigate upstream spoofing of the response itself, which is bounded by the
same trust assumption as runtime honesty above. Later, independently
sourced outcome statements (Section 3.4) are the mechanism by which such
a spoofed confirmation is contradicted over time.¶
Self-attested versus anchored tiers differ in evidentiary weight. A self-attested Capsule is verifiable against its own bytes and signer; an anchored (registered) Capsule additionally resists omission and back-dating through the Transparency Service's append-only log and receipts. A verifier reports the tier it actually verified and never upgrades a claim it could not check.¶
The honest human-in-the-loop flag (Section 5.5) is itself
security-relevant: it prevents a policy auto-approval from being
presented as human oversight. The invariant — human_disposed: true
requires approver: "human" — is structurally guaranteed: a conforming
producer cannot construct a Capsule that violates it, so the
combination simply does not arise in well-formed records, and the claim
is falsifiable from the record alone. A verifier consuming
non-constructor-produced bytes SHOULD assert the invariant defensively
against hand-crafted input (Section 6).¶
The low-entropy digest leakage risk — that a digest over a small
enumeration, short identifier, or bounded value space is recoverable by an
adversary via a dictionary attack, and so is not confidential merely by
being a digest — is given in [I-D.mih-sokolov-scitt-payload-binding]'s
Security Considerations (Low-Entropy Fields). This profile's
reason_digest and evidence_digest fields are subject to that caveat;
producers SHOULD commit such values under a per-tenant salt or via a
tenant-private manifest rather than digesting the bare value.¶
Input integrity is a composable upstream concern. This profile records
what the producer observed and bound at seal time; it does not
authenticate the provenance of inputs delivered to the agent before
sealing. A response spoofed on-path induces an honest confirmed
Capsule for an effect that did not land. Input integrity — binding the
authenticity of request bytes and upstream grounding sources to the
authorization before the seal — is a separate guarantee that composes
with this profile at the digest layer: a producer that holds
input-integrity evidence (a signed tool response, an attested transport
record, a C2PA-style content credential, or an action-body HMAC with
memory provenance attestation) MAY reference it by digest in the Capsule
payload, preserving the verifier's disinterest — the verifier checks the
binding without trusting the producer's claim about upstream systems it
cannot observe. This profile partially addresses the grounding dimension
via the value_grounded constraint (Section 8.1), which checks that
a quoted value matches its cited source, and via model_attestation
(Section 5.1), which constrains the emitter identity. The remaining
input-integrity surface is out of scope for this profile and is addressed
by composing a dedicated input-integrity mechanism upstream.¶
Capsule identity is stable across signing-key rotation. The operator and
developer fields in the Capsule payload (Section 5.1) are plain strings
committed to capsule_id and are independent of the signing key. Rotating a
COSE signing key creates a new Producer Envelope but does not change the
Capsule ID. A verifier accumulating long-horizon history SHOULD correlate
Capsules by payload operator and, when present, epoch_id (Section 5.2),
then apply its own authorization policy to each authenticated envelope key.
A producer SHOULD treat a key rotation that coincides with a configuration
change as an epoch boundary (Section 5.2.2).
See also Section 14 of this document for the data-admission tiers that govern
which runtime context fields MAY enter a Capsule, including the consequence of
the low-entropy digest caveat above for end-user identity fields.¶
Signer authorization is caller-policy territory, not Capsule or envelope
cryptography. The raw public key in kid is self-attested. A verifier relying
on producer identity for a policy decision MUST apply an external authorization
rule to the authenticated key and MUST NOT infer authority from signature
validity alone.¶
A Capsule is content-addressed, tamper-evident, and MAY be anchored to a Transparency Service. As a direct consequence, a committed Capsule cannot be retracted: there is no after-the-fact edit path, and an anchored record is durable beyond the producer's control. Therefore: anything admitted to a Capsule is admitted permanently, and PII or secrets in a content-addressed, tamper-evident, anchored record are unfixable by design. Producers MUST apply a default-deny posture to runtime context before it reaches a Capsule.¶
Producer and adapter authors MUST classify every candidate field into exactly one of the following tiers before admission:¶
Clear-safe — Opaque correlation handles that are joinable but
non-identifying: for example, agent_name, function_call_id,
invocation_id. A field is clear-safe when its value neither identifies a
natural person nor carries content material. These MAY be committed in clear.¶
Digest-only — when a value must be provable later without being disclosed now, it MUST be committed as a digest, never in clear. This tier covers payload content: material a verifier may need to check but that must not be exposed in the record. This tier is realized by the selective-disclosure / detached-payload model (Section 9.2): the Capsule carries only a digest; content is held under deployment controls and disclosed selectively.¶
Never-enters — end-user identity (session identifiers, user identifiers, account handles) and secrets/credentials (tokens, keys) MUST NOT enter a Capsule, in clear or as a digest. Critical: hashing is not anonymization for low-entropy identifiers. Session and user identifiers and similar low-entropy values are recoverable by dictionary attack against their digest (see also Section 13). Therefore a digest of such an identifier is not a safe substitute — the digest re-identifies. Identity MUST be excluded, not digested. Where cross-record or cross-slot correlation of a subject is genuinely required, a pairwise or encrypted correlation identifier SHOULD be used instead of the raw or hashed user identifier.¶
Adapters SHOULD adopt an allow-list stance: enumerate the fields that MAY enter a Capsule (tier 1, plus tier-2 digests) and default-deny everything else. A block-list — enumerating what may NOT enter — fails open: when a runtime adds a new context field in a later version, a block-list silently admits it. An allow-list fails closed, which is the correct direction for a record that cannot be retracted once committed. Adapter authors SHOULD publish the allow-list in adapter documentation so deployers can audit admission without reading implementation code.¶
The author thanks the reviewers and contributors who shaped the design recorded here, and the SCITT and COSE working groups whose substrate this profile builds on. The author additionally thanks Jody Edmondson for identifying the producer-context data-admission problem and the allow-list adapter pattern in capsule-emit issue #22, which shaped the Privacy Considerations of this document.¶