Web4 Evidence Receipts

Conventions and TerminologyThe 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.

IntroductionThis document defines durable, integrity-protected Evidence Receipts for material events in federated and agent-operated systems.

Receipt EventsProfiles MAY define events including assessment issued, admission granted or denied, policy applied, authority granted or revoked, claim challenged or superseded, verification performed, and node lifecycle changes.

Receipt EnvelopeA receipt MUST identify its identifier, event type, actor, subject or object, governing policy, event time, status mechanism, and proof. When an event relies on evidence, the receipt MUST carry references or commitments required by the profile.{ "receipt_id": "urn:web4:receipt:01JEXAMPLE", "event_type": "assessment_issued", "actor_id": "did:example:evaluator-1", "object_id": "urn:web4:assertion:01JEXAMPLE", "policy_id": "urn:web4:policy:admission:v1", "occurred_at": "2026-09-12T13:59:00Z", "status_uri": "https://status.example/receipts/01JEXAMPLE", "proof": { "type": "ExampleProof", "verification_method": "did:example:evaluator-1#key-1", "value": "BASE64URL-SIGNATURE" } }

Issuance and SigningAn issuer MUST integrity-protect each receipt. Corrections MUST use a linked corrective or superseding receipt rather than silent mutation.

Retention and ResolutionPolicy MUST specify a retention class or period. Status MUST remain resolvable for the required retention period.

Evidence CommitmentsA private artifact MAY be represented by a cryptographic commitment. The profile MUST identify the algorithm and any canonicalization, salting, keying, or disclosure procedure.

Research ReferencesA receipt MAY refer to a versioned research artifact using a persistent identifier. Reproducibility-sensitive references SHOULD use a version-specific DOI.

VerificationA Verifier MUST authenticate the issuer, validate integrity, resolve status, check temporal and policy context, and verify disclosed commitments before relying on a receipt.

Relationship to Research ArtifactsBroader Web4 architectural work is described informatively in . Informative research materials MAY be published as versioned scholarly artifacts, including DOI-addressable records.A research artifact is not required for conformance unless expressly incorporated as a Normative Reference by a named profile. Referencing or verifying an artifact does not establish the truth of its conclusions, regulatory approval, certification, security, legal compliance, or IETF endorsement.A Conforming Implementation MUST NOT require access to KCoordinate, KQAS, or another protected internal assessment method unless a separate deployment agreement selects that implementation.

Security ConsiderationsImplementations MUST authenticate issuers, validate proof integrity, check proof purpose, enforce temporal validity, and resolve current status before relying on an object.Implementations MUST address identifier confusion, issuer impersonation, key compromise, algorithm downgrade, replay, stale status, unauthorized supersession, cross-policy confusion, canonicalization ambiguity, denial of service, and fail-open handling of indeterminate validity.Evidence commitments can confirm correspondence with committed bytes but do not prove truth, completeness, legality, provenance, or fitness for purpose. Profiles SHOULD define privacy-preserving commitment procedures for low-entropy artifacts.

Privacy ConsiderationsPersistent identifiers, status queries, proofs, policy references, and linked receipts can enable correlation. Implementations MUST minimize disclosed data and SHOULD use unlinkable or pairwise identifiers where they satisfy policy.Private evidence MAY remain undisclosed and be represented by a cryptographic commitment. Retention and erasure requirements MUST be specified by policy and account for applicable obligations.

IANA ConsiderationsThis document requests no IANA actions.