Revocation

Document: RFC-AITP-0008 Version: 0.1.0-rc.3 Status: Release Candidate Depends on: RFC-AITP-0001 Core, RFC-AITP-0005 TCT

Abstract

AITP defines three revocation surfaces: token revocation via the JTI deny list, key revocation by the identity issuer, and a long-running session re-verification pattern. In the agent-to-agent model, each agent is the authoritative source for revoking the TCTs it issued.

1. Token Revocation (JTI Deny List)

The primary revocation mechanism for v0.1 is a JTI deny list per issuing peer.

1.1 Revoking a TCT

The peer that issued a TCT (its issuer AID) is the only party that can revoke it. Revocation adds the TCT's jti to the issuing peer's deny list. The deny list is consulted by other peers via the issuing peer's ListRevoked HTTPS endpoint (RFC-AITP-0005 §10) or a per-token Verify call.

Wire-level rejection code. A consuming peer that finds a TCT's jti in the issuing peer's signed deny list (after the ordering requirement in §3.3 has been satisfied) MUST reject the TCT with TCT_REVOKED. This is the only correct code for revocation rejection — TCT_EXPIRED is reserved for expires_at being in the past (RFC-AITP-0005 §9.1), TCT_EXPIRES_AFTER_MANIFEST is reserved for the Manifest-bound violation (RFC-AITP-0005 §9.4), and TCT_SIGNATURE_INVALID is reserved for cryptographic signature failure. Implementations that fold revocation into a generic expiry code lose the operator's ability to distinguish "issuer revoked this token early" from "this token reached its natural deadline."

1.2 Deny-list entries

The deny list is internally a set of entry records. Each entry has the shape below; the canonical wire format that wraps these entries (with version, issuer, published_at, expires_at, and a signature) is defined in §1.5 and is the only form peers consume over the network.

{
  "jti": "550e8400-e29b-41d4-a716-446655440000",
  "revoked_at": 1711900000,
  "reason": "key_compromised"
}

The reason field is OPTIONAL informational metadata. Implementations MUST NOT use reason strings in automated decision-making; revocation is a binary state determined solely by the presence of a jti in the signed list.

1.3 Persistence

The deny list SHOULD be persisted to survive restarts. In-memory-only deny lists are acceptable for v0.1 prototypes but not for production use.

1.4 Distribution

Distribution is pull-based in v0.1. A consuming peer SHOULD poll the issuing peer's ListRevoked endpoint with a configurable cadence. Push-based revocation is reserved for a future RFC.

1.5 Signed revocation response

ListRevoked responses MUST be signed by the issuing peer to prevent a network attacker from forging or suppressing entries:

{
  "revocation_list": {
    "version":    "aitp/0.1",
    "issuer":     "<issuing-peer-AID>",
    "published_at": <unix-seconds>,
    "expires_at":   <unix-seconds>,
    "entries": [
      { "jti": "...", "revoked_at": <ts>, "reason": "..." }
    ]
  },
  "signature": "<base64url sig over canonical revocation_list JSON>"
}

The canonical schema is schemas/json/aitp-revocation-list.schema.json.

Verification. A consuming peer MUST verify the signature against the issuing peer's public key (resolved from the issuing peer's Manifest, RFC-AITP-0003). A snapshot whose expires_at is in the past, or whose signature does not validate, MUST be discarded; the peer SHOULD treat the absence of a fresh snapshot per its configured revocation_policy.mode (§3).

Empty lists are signed. Even when an issuing peer has revoked nothing, it MUST publish a signed snapshot with an empty entries array. This prevents a network attacker from suppressing a fresh signed list and serving an older one with revocations stripped.

2. Key Revocation

Identity issuers MAY publish a list of revoked key IDs at their well-known endpoint or a dedicated revocation endpoint:

{
  "revoked_keys": [
    {
      "kid": "key-1",
      "revoked_at": 1711900000
    }
  ]
}

When a key used to sign a peer's identity proof appears in the issuer's revoked-key list, the identity MUST be rejected.

A peer that learns its own AID key has been compromised SHOULD immediately:

1. Revoke all TCTs it issued (add their jti to its deny list).
2. Re-publish its Manifest with a fresh aid derived from a new key pair.
3. Notify any peers it knows of out-of-band.

3. Revocation Policy

revocation_policy:
  mode: fail_closed | fail_open | soft_fail
  max_staleness_secs: 300

3.1 Modes

fail_closed (most secure)

• Issuing peer's ListRevoked endpoint unreachable → reject the request.
• Use for: high-value capabilities, financial actions, irreversible operations.

fail_open (availability-first)

• Endpoint unreachable → allow the request, log a warning.
• Use for: read-only, non-sensitive operations.

soft_fail

• Endpoint unreachable → allow the request with restricted grants.
• Grants restricted to read-only or a configured safe subset.
• The degraded state MUST be logged.

The schema default for revocation_policy.mode is fail_closed (see aitp-trust-anchors.schema.json). Deployments that need availability-first behavior MUST opt into soft_fail or fail_open explicitly; secure-by-default means revocation enforcement does not silently degrade. Production deployments handling high-value capabilities (financial operations, irreversible actions, privileged data access) SHOULD keep the fail_closed default. soft_fail is appropriate only where availability outweighs the risk of operating on a potentially revoked TCT, and the safe-subset restriction has been deliberately configured.

3.2 Staleness

max_staleness_secs defines the maximum age of a cached revocation list. If the cached list is older than this value and the endpoint is unreachable, the configured mode applies.

Related conditional check. The Manifest-expiry bound on the TCT itself (RFC-AITP-0005 §9.4) uses the issuer's Manifest expires_at, not the revocation snapshot's expires_at. The two policies are independent: a TCT may be revoked before its Manifest expires (deny-list hit; TCT_REVOKED), or its Manifest may expire before the TCT does (TCT_EXPIRES_AFTER_MANIFEST when the check is performed and applicable). Implementations MUST NOT conflate the two — both checks can fire for the same TCT.

3.3 Revocation lookup ordering

Implementations MUST verify the TCT's signature, issuer key binding, audience, and expires_at before consulting any network revocation source. The TCT fields issuer and jti are used as lookup keys for the deny list; verifying the signature first ensures these fields are authenticated and cannot be forged by an attacker to trigger attacker-chosen network fetches.

A purely local, side-effect-free revocation check (e.g. an in-memory deny list with no network I/O, no DNS resolution, and no cache write) MAY run before signature verification, since it cannot be exploited for DoS amplification or cache pollution. All network-adjacent revocation lookups — HTTP fetches of ListRevoked, DNS resolution of issuer endpoints, writes to a shared revocation cache — MUST be deferred until after signature verification.

Security rationale. tct.issuer and tct.jti are attacker-controlled bytes until the TCT's signature is verified. An implementation that routes revocation lookups via tct.issuer before signature verification enables:

• Network amplification DoS. The attacker sets issuer to any AID, forcing the verifier to make an HTTP fetch to that AID's revocation endpoint. The fetch is attacker-triggered but originates from the verifier, so the verifier becomes a reflector against arbitrary AIDs.
• Cache pollution. Attacker-chosen jti values, paired with attacker-chosen issuer values, can be inserted into the verifier's revocation cache for AIDs the attacker does not control.
• Telemetry manipulation. Revocation-hit metrics (counters, per-issuer lookup rates, last-fetched timestamps) become manipulable by an off-path attacker who can submit unverified TCTs.
• Side-channel disclosure. Which AIDs the verifier is willing to contact for revocation lookup leaks via outbound DNS / HTTP traffic.

A purely local, in-memory deny-list check (no network I/O, no DNS resolution, no cache writes derived from issuer-provided input) is exempt from this ordering requirement — it cannot be exploited for amplification, pollution, or telemetry manipulation. All other checks — HTTPS fetches of ListRevoked, DNS resolution of issuer endpoints, writes to a shared revocation cache, external calls keyed off tct.issuer or tct.jti — MUST wait until after verify_tct returns success.

Anchoring revocation lookup to a verified issuer and jti removes all four attack surfaces.

The rev-004 conformance fixture pins this ordering: the runner instruments the revocation source and asserts it was NOT called when the TCT signature is invalid (side_effects.revocation_lookup_called: false). An implementation that fetches ListRevoked before signature verification fails the fixture even if it ultimately returns the correct TCT_SIGNATURE_INVALID error code.

4. Session Revocation

For long-running peer interactions, the issuing peer MAY signal revocation by adding the TCT's jti to its deny list. Consuming peers SHOULD periodically re-verify TCTs for long-lived sessions.

Re-verification interval: RECOMMENDED every 5 minutes for sessions lasting more than 1 hour.

4.1 Session invalidation model (v0.1)

In v0.1, "session invalidation" — terminating every active interaction with a specific subject peer — is achieved by revoking every TCT the issuer has ever issued to that subject. There is no separate session-level revocation surface. The deny list (§1) is the single source of truth.

An issuer wishing to terminate all active sessions with peer B MUST:

1. Add every TCT JTI ever issued to B (within their unexpired window) to its deny list.
2. Publish a new signed revocation snapshot (§1.5) reflecting the additions. Empty-snapshot signing rules apply if the issuer had nothing else revoked.
3. OPTIONALLY publish a short-TTL Manifest (RFC-AITP-0003 §8) to accelerate consuming peers' cache expiry — useful when revocations propagate slower than the issuer wants.

A "session-level revoke-all" API (one operation that covers a subject without enumerating individual JTIs) is reserved for a future RFC. v0.1 implementations SHOULD surface per-JTI revocation as the primary admin API; bulk-revocation-by-subject is a quality-of-life concern, not a protocol requirement.

Limitation (issuer JTI history). An issuer that does not maintain a complete history of issued JTIs cannot guarantee total session revocation — it can only revoke the JTIs it remembers. Issuers SHOULD persist issued JTIs at least until max(issued_tct.expires_at) for the relevant subject so the bulk-revocation operation above is complete. After that point all unrevoked TCTs are guaranteed expired, so the JTI is no longer needed for session-revocation completeness; it MAY be garbage-collected from the issuer-side history table.

This is an issuer-side persistence requirement and is not visible on the wire. It is a SHOULD (not a MUST) because the deficiency manifests as an issuer's inability to enumerate its own subject TCTs rather than as a protocol-level error a peer can observe; an issuer that fails to enumerate is silently providing weaker session-revocation guarantees than its consuming peers will assume. See §1.3 for the related deny-list persistence guidance — the deny list and the issued-JTI history are two distinct issuer-side structures with the same persistence motivation.

5. Security Considerations

• The issuing peer's ListRevoked endpoint is itself a trust surface; it MUST be served over HTTPS, and its responses SHOULD be signed by the issuing peer.
• fail_open trades security for availability and MUST NOT be the default for high-value operations.
• Clock skew between the issuing peer and consuming peers reduces effective revocation latency. Implementations SHOULD use a monotonic clock when comparing revoked_at.
• A compromised peer can stop honoring its own revocations. Defense in depth: high-value operations SHOULD use short TTLs (RFC-AITP-0005 §8.1) so that revocation latency is bounded by the TCT lifetime.

6. References

• RFC-AITP-0001 Core
• RFC-AITP-0003 Agent Manifest
• RFC-AITP-0005 TCT
• RFC-AITP-0007 Key Resolution