]> Individual Contributor

Dubai United Arab Emirates shameerthaha@gmail.com

Individual Contributor

United Arab Emirates shaibis@gmail.com

Security Workload Identity in Multi System Environments WIMSE AI agent audit evidence SCITT The WIMSE AI Identity Management System (AIMS) requires tamper-evident agent audit logs but does not specify their format or discovery. This document maps the AIMS minimum fields to the SCITT Agent Execution Evidence profile, defines one claim that binds a workload credential to the persistent agent, governing policy, expected Evidence Service and optional Assurance Statement, and defines an in-toto predicate type for carrying Execution Receipts alongside the in-toto agent audit record format. It also describes how a service admits an agent's call by checking its assurance at the moment of the request, and defines an HTTP field that links each call to the caller's evidence. It is a companion to the AIMS work and makes no change to it. The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the WIMSE Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction Section 11 of ("Agent Monitoring, Observability and Remediation") requires tamper-evident audit logs and lists the fields an audit event must record at a minimum. Section 8 does not require any particular posture assessment mechanism or evidence format, and Section 13 states that compliance criteria are out of scope. That is a reasonable division: an identity management framework should not pick a log format. It leaves four practical questions open for an implementer: In what format are the seven minimum fields recorded so that a party other than the operator can verify them? Given an agent's credential, how does a relying party learn which Evidence Service and policy to expect that evidence under, and which assurance statement applies? Before acting on a call, how does a Serving Party decide, for that call, that the calling agent is registered, currently assured at the level the operation requires, and acting for a Principal entitled to it? When a request passes through several agents, how are the principal of the transaction and the Actor Chain carried with it and recorded on each side? answers the first question with per-call Execution Receipts and Assurance Statements registered through SCITT , and supplies the admission records and linking rules behind the third and fourth. This document answers the second with one claim, aee_evidence, that an identity server MAY place in a Workload Identity Token or other agent token; the third with the admission procedure of ; and the fourth with an HTTP field and the use of nested act claims (). It also maps the AIMS fields and defines an in-toto predicate so that the formats compose with . The decision to act is made per call because what it depends on changes between calls: an agent's assurance can be suspended within minutes, one agent can act for many Principals with different permissions, and operations on one service differ in risk. Section 3.4.11 of requires that "each hop in the chain MUST explicitly scope and re-bind the security context"; recording that re-binding on both sides of every hop is what lets it be verified afterwards. This document is short by design. It proposes one claim, one predicate type and one HTTP field, and defers everything else to the documents it cites. It is a companion to , not proposed text for it. AIMS states the properties audit evidence must have; this document is one mechanism that provides them, and others can do so alongside it. The Agent Registration Authority identity model and the Evidence Service named in each token are deployment choices of this document, not properties AIMS would need to adopt.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. The terms Agent, Agent Identity Management System and Workload are used as in . Actor and Delegation are used as in , and Call Chain and Transaction as in . Actor Chain, Admission, Agent Registration Authority, Agent Registration Statement, Assurance Statement, Bundle, Caller Reference, Calling Agent, Evidence Chain, Evidence Service, Execution Receipt, Linked Verification, Policy Pack, Principal Link, Serving Party and Supervisory Authority are used as defined in , which states which of them have no equivalent in other IETF specifications. Issuer, Transparency Service, Signed Statement and Receipt are used as in .

Problem Statement Section 11 of states that, at a minimum, audit events MUST record: the authenticated agent identifier; the delegated subject (user or system), when present; the resource or tool being accessed; the action requested and the authorization decision; a timestamp and a transaction or request correlation identifier; the posture assessment or risk state influencing the decision; and remediation or revocation events and their cause. Five things are needed for a relying party to act on such a log, or on a call, that the framework does not supply:

Format:

A field list is not a format. Two operators recording the same seven fields in their own schemas cannot be verified by one tool.

Discovery:

A relying party presented with an agent credential has no standard way to learn which Evidence Service is expected to hold the agent's audit evidence, whether it is registered anywhere independent of the operator, or which policy was in force. Discovering and retrieving the evidence itself is a further step that requires deployment configuration or another protocol.

Binding:

Even when the log is found, nothing in the credential ties the credential to the log. A log entry carrying an agent identifier is only as strong as the link between the identifier, the key, and the entries before and after it.

Admission:

The claim lets a relying party find evidence after the fact, but a Serving Party needs to decide before acting, on every call, because assurance status and delegated authority can change between calls.

Chains:

Correlating events across chains or systems needs additional context. Without it, each hop's evidence stands alone and cannot show who started a request, for which Principal, or whether authority widened along the way.

The remainder of this document addresses each in turn.

Mapping of AIMS Minimum Fields to the Execution Receipt The following list maps each minimum field of Section 11 of to the member of the Execution Receipt Statement defined in Section 6.7 of that carries it. Integer keys are those of the CBOR form; names are those of the JSON form.

Authenticated agent identifier:

agent_id (9), the runtime identity in force, which the Agent Credential Statement maps to a logical_agent_id issued by an Agent Registration Authority and binds to a key. On a Serving Party's admission receipt, caller_agent_id (20) is the calling agent's identifier as authenticated.

Delegated subject, when present:

principal (10), with the Actor Chain actor_chain (23) when the agent acts for another agent's request, and principal_link (24) when two parties to a call must show they recorded the same Principal. Natural persons are carried as a peppered digest, not in clear.

Resource or tool being accessed:

target (16) and egress_host (17). Tool name or model identifier; host for network egress.

Action requested and authorization decision:

record_type (4), decision (6) and request_digest (12). record_type is an event category, not the requested operation; decision is one of allow, block, confirm or record as reported by the producer, and a confirm is followed by a receipt recording its allow or block outcome, which names it in confirm_seq (19); request_digest commits to the request bytes but does not disclose the requested action without a validated pre-image.

Timestamp and correlation identifier:

ts (14), seq (2), task_seq (11) and parent_seq (5). ts is producer-declared. seq is unique within an Evidence Chain, and parent_seq links a tool call to the inference that requested it; both are interpreted inside one Evidence Chain, in which task_seq names the Task by the seq of its task_start. Across chains and systems, txn (25) is the transaction identifier of , carried on both sides of every call, and an admission receipt's caller_ref (21) names the caller's receipt for the call. txn and caller_ref correlate the two sides; they do not show that both sides recorded the same request. call_digest (29) establishes that, as the two sides compute it over the same representation of the request. This follows the separation of correlation from matching in . Equal sequence values in distinct chains do not identify the same event.

Posture or risk state influencing the decision:

policy_pack_digest (7) and config_integrity_digest (8) commit to the policy and configuration the Evidence Service declares was in force. The applicable Assurance Statement records the assessed capability scope, risk assessment and monitoring summary; these are assessment-level values, not necessarily the per-event posture that influenced a decision. A richer per-event posture record can be carried by .

Remediation or revocation events and their cause:

Revocation Statement (aee-type 8), Configuration Drift Statement (aee-type 4), an Assurance Statement disposition of reassess, suspend or withdraw, and a RESTRICTED or SUSPENDED status set by the Supervisory Authority, all registered on or referenced from the same Transparency Service. A refused call is recorded as block, at the caller's Decision Point or in the Serving Party's admission receipt. reason_code exists only on a Revocation Statement and carries a revocation cause; a Configuration Drift Statement carries prev_config_digest, new_config_digest and the changed entries instead. Recording drift, revocation or a disposition does not by itself prove that a remediation instruction was enforced; the enforcement outcome requires additional audit evidence.

The mapping is therefore partial: every AIMS minimum field has a carrier in a signed, hash-chained receipt or a registered statement referenced from it, but those carriers are commitments and producer-reported values rather than the underlying facts. A digest does not disclose its pre-image, a decision is what the producer recorded, policy and configuration digests commit to what the Evidence Service declares was in force, the Assurance Statement's risk state is assessment-level rather than per-event, and a recorded remediation event is not proof of enforcement. Missing decision context is disclosed by the format, not inferred from an event code or digest; deployments that need it SHOULD use the audit record of , linked as described in .

The aee_evidence Claim This section defines one claim. It MAY appear in a Workload Identity Token , in a JWT or CWT access token issued to an agent under Section 10 of , or in any other JWT or CWT that identifies an agent. Recipients that do not understand it ignore it, as those specifications require.

The value has the following members. evidence_service, policy_pack_digest and logical_agent_id are REQUIRED.

evidence_service (CBOR key 1), REQUIRED:

A URI identifying the Evidence Service that issues Execution Epoch Statements, or individually registered Execution Receipt Statements, for this agent. The URI is the Issuer identifier that appears in the iss claim of those statements' CWT Claims header. It is an identifier, not necessarily a retrievable location.

policy_pack_digest (CBOR key 2), REQUIRED:

The pack_digest of the Policy Pack Statement that governs this agent at the time the token is issued, in the digest form of . In the JSON form, an object {"alg": "sha-256", "value": "<base64url>"}; in the CBOR form, the array [alg, value].

transparency_service (CBOR key 3), OPTIONAL:

The base URI of the Transparency Service with which the Evidence Service registers statements, and from which a relying party can resolve registration artifacts through . It identifies the service, not a particular Bundle or evidence period.

agent_credential_digest (CBOR key 4), OPTIONAL:

The digest of the Agent Credential Statement payload that binds this agent's identifier to the key in the token's cnf claim. When present, the public key represented in the Agent Credential Statement MUST equal the key in cnf; equality is of the represented cryptographic public keys, not of the JWK or COSE_Key encodings, which can differ for the same key. Its presence enables the credential-key-bound result of ; its absence leaves the claim as identity-and-policy correlation only.

logical_agent_id (CBOR key 5), REQUIRED:

The persistent identifier of the agent across runtime environments, equal to the logical_agent_id of the Agent Credential and Agent Registration Statements: a did:web identifier in the domain of the Agent Registration Authority that issued it. Section 6 of requires that an agent be assigned exactly one WIMSE identifier; within any one such deployment, that identifier is the agent's runtime identity there, and logical_agent_id names the agent above the runtime identities of all its deployments.

assurance_statement_digest (CBOR key 6), OPTIONAL:

The digest of the applicable Assurance Statement payload. The statement carries the authoritative assurance_level, assessed capability scope, risk assessment, monitoring summary, validity and status.

assurance_level (CBOR key 7) and assurance_status (CBOR key 8), OPTIONAL:

The level of the Assurance Statement named by assurance_statement_digest, and the status value its token issuer observed in the statement's status list when issuing the token. They are a signed cache of the statement, for a fast admission decision, and MUST be present together and only with assurance_statement_digest. A token issuer MUST NOT include them unless it checked the status when issuing the token. A Serving Party MAY rely on them only if status_checked_at is present and well-formed, is not later than its clock plus its skew allowance, and is no older than the status freshness its policy requires for the operation; this is independent of the token's validity period. Otherwise it MUST NOT rely on them and obtains the status from the status list itself. If they disagree with the statement, the statement prevails.

status_checked_at (CBOR key 10), OPTIONAL:

The time at which the token issuer observed assurance_status in an authenticated status list, in seconds since the Unix epoch (a NumericDate in JSON). It is signed inside the token, and it MUST be present when assurance_level and assurance_status are present. The freshness rule above applies to the age of this observation, not to the remaining lifetime of the token: a token with 30 seconds left can carry an hour-old observation.

registration_digest (CBOR key 9), OPTIONAL:

The digest of the Agent Registration Statement payload for logical_agent_id.

The claim identifies the expected Evidence Service, the policy commitment, the persistent logical identity, optional registration, credential and assurance bindings and an associated Transparency Service. It does not identify a particular Bundle or evidence period, and it is not a retrieval protocol: Bundle discovery and retrieval are supplied by deployment configuration or another protocol and are outside this document. This document assumes a token profile in which the authenticated sub names the workload that is authenticating; logical_agent_id names the agent that workload is an instance of, and the two differ whenever an agent runs under more than one identity. Section 3.1.2 of states that a workload identifier "MAY represent a logical workload, a service implemented by one or more workloads, or a specific workload instance, depending on deployment policy", and that "two credentials containing the same workload identifier value represent the same workload only when validated under the same trust domain and issuer trust configuration". A relying party that receives tokens for the same agent from a development cluster, a production cluster and a cloud identity platform therefore sees three unrelated sub values. Carrying logical_agent_id in the token gives it the correlation key, and the Agent Credential Statement found through evidence_service gives it the signed, registered mapping from that key to each runtime identity and its validity window, so that correlation is verified rather than assumed. JWT and CWT are containers whose profiles assign different meanings to sub: in a profile where sub names a delegated user or system while the agent acts as a separate actor, the mapping from the token's subject to the agent's runtime identity MUST be separately specified, and does not apply to the token's sub directly. Example, as it would appear in a WIT:

Relying Party Behaviour A relying party that receives a token carrying aee_evidence and that wishes to verify the agent's conduct: Validates the containing token under its own profile, including issuer, protection, audience, validity and proof of possession where the profile uses one. None of the following steps adds trust to a token that fails its own validation. Establishes the Evidence Service and Transparency Service trust anchors it accepts, obtained out of band or under an accepted retrieval and trust policy. A URI carried in the token, including transparency_service, is not a trust anchor, and keys reached from a token-supplied location become trusted only under that policy. Identifies the evidence period it requires and whether it needs historical verification, that is, what was registered and what status evidence existed at that time, or current acceptance. Obtains a Bundle for that period from the Evidence Service or from the agent's operator, by means outside this document. Verifies the Bundle per Section 9 of against the trust anchors of step 2. Checks each of the following bindings, reporting each failure by kind: issuer binding: the iss of the Execution Epoch Statements, or of individually registered Execution Receipt Statements, equals evidence_service; runtime identity: the Agent Credential Statement lists the token's authenticated workload identity among its runtime_identities (in a token profile where sub is that identity, this is the token's sub); logical identity: the Agent Credential Statement's logical_agent_id equals the claim's logical_agent_id, and the Agent Registration Statement it names was issued by an Agent Registration Authority the relying party accepts (and, if registration_digest is present, has that digest); policy binding: every receipt's policy_pack_digest equals the claim's policy_pack_digest, or equals a registered descendant in the Policy Pack lineage that an explicit relying-party rule, an accepted Assurance Statement or another configured policy-evaluation result permits. Registration and ancestry do not by themselves establish that a descendant is semantically more restrictive, and a digest mismatch alone does not show that a policy was weaker or that execution under the declared policy occurred. If agent_credential_digest is present, checks that the Agent Credential Statement in the Bundle has that digest and that the public key it represents equals the key in the token's cnf, compared as cryptographic keys rather than encodings. Success produces a credential-key-bound result; the claim's validity without agent_credential_digest is limited to the basic identity-and-policy correlation of the other steps. If assurance_statement_digest is present, checks that the Bundle contains that Assurance Statement, that its logical_agent_id, credential, policy and configuration bindings match, and that its level, scope, validity, monitoring and status satisfy relying-party policy, applying configured freshness rules to the required status evidence. The absence of a Revocation Statement or of an adverse status entry in a supplied Bundle establishes only what that Bundle's snapshot supports; it does not establish current non-revocation. An issuer, runtime-identity, logical-identity or policy-binding failure at step 6 is a distinct conclusion: evidence produced for a different agent is an identity failure, not a policy downgrade, and a policy mismatch is a downgrade conclusion only where the relying party's rules support it. The claim does not itself make token validation depend on evidence availability. Token validation, workload authentication, access authorization and evidence acceptance are separate decisions: an access token does not necessarily function as an authentication credential, and acceptance for an operation is governed by the containing token's profile and relying-party policy. A relying party MAY require acceptable evidence before permitting an operation, and the absence of evidence cannot satisfy such a policy. A recipient that does not understand the claim ignores it; where evidence is required by policy, an unrecognized claim is not a successful evidence verification.

Admission by a Serving Party A Serving Party that admits calls from agents only if they are registered and assured performs the following steps on every call, before acting on it. They decide the call; the steps of verify conduct after the fact, and the two are separate. Validate the token and the proof of possession for this request under the applicable credential and authentication profiles; defines the Workload Identity Token, while its proof-of-possession mechanisms are specified separately. Determine the Assurance Statement and Agent Registration Statement that apply, from aee_evidence or by other configured means, and their status. The status MUST be no older than the freshness the Serving Party's policy requires for the operation. A token's assurance_level and assurance_status MAY be used as that status only under the rule on status_checked_at in ; if that rule is not met, the Serving Party checks the status list itself. For operations its policy marks as high-risk, the Serving Party SHOULD check the status list itself. Check that the registration is from an accepted Agent Registration Authority and is valid; that the Assurance Statement's level meets the minimum the Serving Party's policy sets for the operation, from an accepted assessor and scheme; and that its status is VALID, or RESTRICTED with the operation within the restricted class the scheme defines. Check the Principal and the current actor, the outermost act of the Actor Chain (), against its policy for the operation, including any status of the Principal's delegation and any minimum Principal assurance it requires. As requires, the access-control inputs are the token's top-level claims and the current actor; prior actors are informational only and MUST NOT be used to decide admission. The Actor Chain is attribution, not authority: at admission it is the token issuer's asserted history, which is neither complete nor evidence that any hop held or narrowed authority. Where AEE-Caller-Ref is present, compute call_digest over the request received, as defined in Section 6.7 of ; never use the value the caller presents. Refuse the call if cd is present and differs from the computed value, or if cd is absent while the Serving Party's policy requires linking. Refuse the call if its caller reference names a caller receipt that an earlier admission of this Serving Party already names (Section 6.7.2 of ). Produce an admission receipt recording the decision and its basis, as Section 6.7.2 of specifies, whether the call is admitted or refused. The receipt records the call_digest computed in step 5 and, in admission_basis, the time of the status observation relied on, which is the token's status_checked_at where the token's cached status was used. It is not the time of admission. Act on the call, or refuse it. A Serving Party that cannot complete a step refuses the call. The absence of evidence does not satisfy a policy that requires it. A Serving Party cannot check the caller's egress_host against its own hosts at admission, because it does not see the caller's receipt. That check is made in Linked Verification (Section 9.1 of ).

Carrying the Caller Reference and Actor Chain

The AEE-Caller-Ref Field A Calling Agent that makes an HTTP request to a Serving Party includes the AEE-Caller-Ref request header field. It is a Dictionary Structured Field with the following members:

es:

A String: the Issuer identifier of the Calling Agent's Evidence Service.

seq:

An Integer: the seq of the Calling Agent's Execution Receipt for this call.

h:

A Byte Sequence: the record-hash of that receipt.

txn:

A String: the transaction identifier. When the request carries a Transaction Token , it MUST equal that token's txn claim.

cd:

A Byte Sequence: the call_digest value of the Calling Agent's receipt for this call, that is, the digest bytes only, which are SHA-256 for HTTP. It is REQUIRED when that receipt carries call_digest.

Token claims, such as aee_evidence, bind the agent and its policy across the calls a token covers; AEE-Caller-Ref binds one call. A caller reference MUST NOT be carried in a token that can be presented on more than one call. Unknown members are ignored. For example, with a line break added for display:

The Serving Party copies es, seq, h and txn into the caller_ref and txn of its admission receipt. It never copies cd: the call_digest of its receipt is the value it computed itself over the request it received (). They are the caller's claim until Linked Verification checks them against the caller's registered chain (Section 9.1 of ). The Calling Agent's receipt is produced before the request is sent, so the hash is available when the field is built.

Actor Chain and Principal Link The Actor Chain travels in the token presented on the call as nested act claims (), the outermost naming the Calling Agent. Both parties record it as actor_chain, least recent first. Each party computes the principal_link as SHA-256 over the octets of the access token in the request's Authorization header field (not the Workload Identity Token or proof token), so no further field is needed. A Serving Party uses only the current actor in its admission decision (); prior actors are audit history, recorded and checked for consistency by Linked Verification, and the chain carries attribution, not authority. Authority carried across hops needs per-hop signed evidence, such as a delegation chain or the linked receipts of Section 9.1 of ; showing that authority narrowed at each hop remains an open issue of that document.

Other Protocols Protocols other than HTTP that carry agent calls, such as tool-invocation protocols, can carry the same members in the metadata they provide for each request. This document does not define those bindings.

Composition with the Agent Audit Record defines an audit record as an in-toto Statement in a DSSE envelope , canonicalized with , with a predicate type of its own. That format is richer per event than an Execution Receipt and records vantage, posture and observed effect. The two are complementary: the audit record describes an authorization decision in depth; the Execution Receipt places the call on an identity-bound chain sealed into a Transparency Service. To let one toolchain carry both, this document defines an in-toto predicate type for the Execution Receipt.

The predicate is the JSON form of an Execution Receipt as defined in Section 6.7 of , unchanged. The Statement's subject MUST contain one entry whose name is the decimal seq of the receipt and whose digest contains sha256 set to the hex-encoded SHA-256 of the JCS serialization of the receipt JSON object, including agent_sig when present; this is the JSON-form record-hash of . Conversion from the CBOR form changes the bytes and therefore the digest and the epoch inclusion proof: a JSON predicate converted from CBOR MUST NOT be presented as carrying the CBOR record-hash or its epoch proof. Where the CBOR chain must be preserved, the original artifact is carried and verified together with an explicit binding to the JSON representation. The DSSE payloadType is application/vnd.in-toto+json. An audit record per and an Execution Receipt for the same call are associated through two verifiable commitments: The Execution Receipt's request_digest MAY be the digest of the audit record's decision.requestDigest pre-image, so that both commit to the same request bytes once the pre-image is validated. The audit record MAY point to the Execution Receipt for the same call, for example by its record-hash or by the SCITT Receipt that registers it. Such a pointer associates the two records and dates neither of them. A SCITT Receipt for the Execution Receipt proves the inclusion of that receipt, not of the audit record's envelope, so it is not a transparency-log anchor under and is not carried in correlation.externalAnchor. Dating the audit record through SCITT would need a Signed Statement registered over the audit record's envelope digest; this document does not define one. Neither document is required for the other: deployments may implement either format independently where their requirements permit. Conformance to or to is determined by each document's full set of applicable requirements, not by the presence of an artifact of the expected name, and the strength of a cross-format association depends on the verified commitments and registration proofs and on each format's observation scope. An operator that produces both and links them as above gives a relying party a sealed chain and a rich decision record for the same call. In the terms of , the Execution Receipt is an Action Record produced at the Harness vantage, the admission receipt is the corresponding record at the Serving Party, and the aee_evidence claim is part of the audit context carried with the agent's credential.

Security Considerations The claim is a pointer and a commitment, not a proof. It is protected by the signature on the token that carries it, and it is only as trustworthy as the identity server that issued the token. A compromised identity server can point a relying party at a colluding Evidence Service; the check is the Transparency Service, whose Receipts are verifiable independently of both. Registration itself is limited evidence: a Receipt establishes that a statement was registered with a Transparency Service, not that the statement is truthful, that the evidence is complete, or that it covers all relevant activity ( describes the accuracy and selective-registration limits). Acceptance therefore also depends on trusted Issuers and Evidence Services, on any applicable runtime appraisal and on independent observation. Nor is a token-supplied location a trust anchor: Evidence Service and Transparency Service keys are trusted only when obtained out of band or under an accepted retrieval and trust policy, and following a validly signed pointer to an untrusted service does not make that service trusted. The policy_pack_digest in the claim lets a relying party compare the declared policy commitment with the digests in receipts. It does not prevent downgrade; a relying party that does not check it gains nothing from it, and one that accepts any registered descendant of the declared pack accepts a weaker policy whenever an attacker can register one. Whether a descendant is acceptable belongs in explicit relying-party policy, not in the digest comparison itself. An assurance_statement_digest is a binding, not a guarantee. The referenced statement can expire, become stale under its monitoring frequency, or be suspended or withdrawn after token issuance. A relying party that uses it MUST perform the SCITT verification and status checks at decision time. A Bundle is a snapshot of what its producer chose to include: the absence of revocation information in a supplied Bundle does not establish current non-revocation, and a relying party that requires current acceptance applies configured freshness rules to the status evidence. assurance_level and assurance_status in a token can be as stale as the status_checked_at that the Serving Party's policy accepts; the token's validity period does not bound it. The freshness rule of bounds this, and the Serving Party's own status check for high-risk operations removes it where it matters most. status_checked_at is signed inside the token, so a token issuer that misstates it is detectable only against the status list. A Serving Party or relying party that requires tight freshness SHOULD check the status list itself for high-risk operations, as in . The AEE-Caller-Ref field and the act claims are assertions by the Calling Agent. A field naming a receipt that does not exist fails Linked Verification with E_CALLER_REF. One naming a different real call, such as a payment of another amount under the same token and transaction, fails with E_CALL_MISMATCH, because the call_digest values differ. One naming the same request sent to a service under a different host fails with E_SERVING_HOST, because the caller's egress_host is not among the hosts the Serving Party declared. Services behind one shared gateway host are told apart only by the request-target that cd binds and by the gateway's routing, which no receipt records (Security Considerations of ). A Serving Party refuses at admission a call whose cd differs from the value it computed. A replayed field is refused by the Serving Party that already admitted it, and detected by Linked Verification when used at another, except that behind a shared gateway host a wrong-backend admission can still pass when only that admission is included in the Linked Bundle (Security Considerations of ). A Serving Party that acts before verifying them relies on its own checks of the token and the Principal, not on the field. Including transparency_service in the token reveals to any token recipient which Transparency Service the operator uses. Operators who consider that sensitive omit it and distribute the Transparency Service's identity out of band. The security considerations of , and apply.

Privacy Considerations The claim carries no information about a Principal, no content, and no per-call data. It adds an Evidence Service identifier, a policy digest, a persistent logical_agent_id, and optional credential and Assurance Statement digests. The logical identifier intentionally makes one agent linkable across its runtime platforms; repeated digest values can also be correlated. A relying party MUST accept that correlation only through an Agent Credential Statement from an accepted Issuer that maps each runtime identity and trust domain to the logical agent. The digests do not disclose the committed payloads. AEE-Caller-Ref reveals the Calling Agent's Evidence Service and a transaction identifier to the Serving Party, and the act claims reveal which operators' agents took part in a request. Calling Agents SHOULD send them only to the Serving Parties they call. The privacy considerations of , in particular its treatment of natural-person Principals, apply to the evidence the claim points to.

IANA Considerations

JSON Web Token Claims IANA is requested to register the following claim in the "JSON Web Token Claims" registry . Claim Name: aee_evidence Claim Description: Evidence service, policy, persistent identity and optional registration and assurance binding for agent execution evidence Change Controller: IETF Reference: of this document

CBOR Web Token Claims IANA is requested to register the following claim in the "CBOR Web Token (CWT) Claims" registry . Claim Name: aee_evidence Claim Description: Evidence service, policy, persistent identity and optional registration and assurance binding for agent execution evidence JWT Claim Name: aee_evidence Claim Key: TBD1 Claim Value Type: map Change Controller: IETF Reference: of this document

HTTP Field Name IANA is requested to register the following field in the "Hypertext Transfer Protocol (HTTP) Field Name Registry" per : Field Name: AEE-Caller-Ref Status: permanent Structured Type: Dictionary Reference: of this document

IETF URN Sub-namespace IANA is requested to register the sub-namespace aee in the "IETF URN Sub-namespace for Registered Protocol Parameter Identifiers" registry per , with this document as the reference and the IETF as the change controller, and within it the identifier urn:ietf:params:aee:predicate:execution-receipt as defined in .

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. 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. W3C Credentials Community Group in-toto project secure-systems-lab

Acknowledgements The authors thank the authors of , and , whose work this document is intended to connect rather than duplicate. The authors thank Iman Schrock for her review of linked verification and status freshness in the -00 drafts, Jiahui Miao for reviewing the split between token claims and the caller reference, Sankalp Gilda for reviewing the composition with the audit record, and Kieran Sweeney for reviewing the use of the Actor Chain.

Changes since -02 This section is to be removed before publication as an RFC. The statement that a replayed caller reference is detected at another Serving Party now carries the qualification of the SCITT draft: behind a shared gateway host, a wrong-backend admission can still pass when only that admission is in the Linked Bundle, as raised by Iman Schrock.

Changes since -01 This section is to be removed before publication as an RFC. The posted -01 was uploaded from an earlier commit and did not contain the revisions listed under "Changes since -00" for the Actor Chain, the caller reference and the audit-record reference; this revision does. Admission follows Section 4.1 of RFC 8693: the access-control inputs are the token's top-level claims and the current actor. Prior actors are audit history in actor_chain, are not used to decide admission, and are checked for consistency by Linked Verification (, ). The wording that a Serving Party checks every Actor, "as RFC 8693 permits", is removed. At admission the recorded Actor Chain is stated to be the token issuer's asserted history, neither complete nor evidence of authority. Admission that depends on the full actor history is left to an open issue of , for discussion at IETF 127. Updated references to the -02 revision of the SCITT draft.

Changes since -00 This section is to be removed before publication as an RFC. Added status_checked_at (CBOR key 10) to aee_evidence. The freshness rule now applies to the age of the status observation, independent of token validity, and the "remaining lifetime" rule is removed (). Added the cd member to AEE-Caller-Ref, carrying the caller's call_digest, and regenerated the example (). A Serving Party computes its own call_digest, and refuses a call whose cd differs. A Serving Party MUST refuse a caller reference it has already admitted. The admission receipt records call_digest and the status observation time (). Corrected the statement in the Security Considerations that a forged caller reference always fails Linked Verification; the failure cases and the replay rule are now listed. Noted that services behind one shared gateway host are told apart only by the request-target and the gateway's routing. Updated references to the -01 revision of the SCITT draft, and added EP-AEC as an informative reference. Stated the split between token claims, which bind the agent and its policy, and AEE-Caller-Ref, which binds one call; a caller reference MUST NOT be carried in a token that can be presented on more than one call (). An audit record's pointer to an Execution Receipt or its SCITT Receipt dates neither record and is not carried in correlation.externalAnchor (). Updated the audit-record reference to -02. The Actor Chain carries attribution, not authority; authority carried across hops needs per-hop signed evidence, such as a delegation chain or linked receipts, and showing that authority narrowed at each hop remains open (, ). Added Jiahui Miao, Sankalp Gilda and Kieran Sweeney to the Acknowledgements. Stated that this document is a companion to AIMS and not proposed text for it, and renamed now that the audit-record draft is no longer a WIMSE draft.