Transitive CLEAR Revocation and Composite Physical-Safety Windows for Multi-Hop Autonomous Agent DAGs

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Table of Contents

1. Introduction and Problem Statement

In multi-agent workflows, revoking a parent agent's token leaves already-spawned downstream sub-agents free to execute stale tool calls against enterprise or industrial infrastructure. Existing delegation specs lack a transitive DAG epoch heartbeat and a cryptographic Purdue-zone firewall bit that unconditionally blocks autonomous writes to Level 0, Level 1, and Level 2 Programmable Logic Controllers (PLCs) and Safety Instrumented Systems (SIS).¶

This specification complements the foundational execution-trace verification architecture defined in draft-durga-agenttrust-trace-verification-00 by introducing deterministic, fail-closed wire semantics specifically addressing Transitive CLEAR DAG Revocation & OT Firewall.¶

2. 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 ([RFC2119] [RFC8174]) when, and only when, they appear in all capitals, as shown here.¶

3. Transitive CLEAR Token and OT Zone Firewall Profile

Every node in a multi-hop agent execution DAG MUST carry and verify a signed CLEAR DAG Envelope prior to executing any downstream tool call:¶

{
  "clear_version": "1.0",
  "dag_root_id": "urn:uuid:9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d",
  "hop_index": 3,
  "parent_node_hash": "sha256:4b227777d4dd1fc61c6f884f48641d02b4d121d3fd328cb08b5531fcacdabf8a",
  "composite_window_start_ms": 1793404800000,
  "composite_window_end_ms": 1793404805000,
  "clear_revocation_epoch": 19,
  "effect_class": "ACTUATE_ADVISORY",
  "target_purdue_zone": "PERA_LEVEL_3_MES",
  "sis_hardware_interlock_present": false,
  "signature": {
    "alg": "Ed25519",
    "kid": "sha256:b600306cfa76723fdec395e53a9b3d9fdb78b1e2d7a23c32fcbcd2dc6d0c4092",
    "sig": "Ns1GRnHE2CtxrTdUqpjcxTq1Wpn_1VEx-zuUNz63I9hzBkJoruECGHT4sRFyLQfkX9meQ7BfxkjhlQ08wY0uDQ"
  }
}

4. Normative Fail-Closed Verification Rules

Conforming verifiers and relying-party gateways MUST enforce the following deterministic invariants before releasing any downstream side effect:¶

1. TRANSITIVE_ANCESTOR_REVOCATION: If any ancestor node in dag_root_id broadcasts a signed CLEAR abort frame or increments clear_revocation_epoch, all descendant nodes MUST immediately abort pending tool calls and release held resource leases within one heartbeat interval.¶
2. COMPOSITE_WINDOW_CONTAINMENT: At every hop i, the child execution window [start_i, end_i] MUST be a strict subset of its parent's window [start_{i-1}, end_{i-1}], and execution MUST fail closed if current_time > composite_window_end_ms.¶
3. OT_PURDUE_L0_L2_FIREWALL: Any agent invocation targeting target_purdue_zone in {PERA_LEVEL_0_PROCESS, PERA_LEVEL_1_BASIC_CONTROL, PERA_LEVEL_2_SUPERVISORY} with effect_class != READ_ONLY MUST be unconditionally rejected by the protocol gateway.¶

5. Strict Parser Determinism and Wire-Level Input Hardening

In multi-hop industrial and enterprise agent DAGs, a single permissive parser on an intermediate hop can allow a revoked or expired branch to actuate downstream systems. Conforming CLEAR DAG verifiers and OT zone gateways MUST enforce five pre-canonicalization parser invariants:¶

1. DUPLICATE_KEY_REJECTION: The JSON parser MUST reject any CLEAR envelope containing duplicate keys (such as duplicate target_purdue_zone or effect_class fields) at parse time before policy evaluation.¶
2. IEEE754_FINITE_SAFE_INTEGER_BOUNDS: All epoch and window fields (hop_index, composite_window_start_ms, composite_window_end_ms, clear_revocation_epoch) MUST be exact JSON integers within [0, 2^53 - 1]. Boolean types, string-coerced integers, and non-finite IEEE-754 floats (NaN, Infinity, 1e1000) MUST fail closed.¶
3. CYCLE_SAFE_TRANSITIVE_DAG_VERIFICATION: Verifiers MUST track visited node digests along the parent_node_hash chain and immediately reject any cyclic graph or hop depth exceeding the policy maximum.¶
4. CANONICAL_HEX_AND_BASE64URL_ENFORCEMENT: parent_node_hash and kid MUST match ^sha256:[0-9a-f]{64}$, and sig MUST be canonical unpadded Base64url with zero non-zero trailing pad bits.¶
5. EVIDENCE_TO_RULE_BYTE_BINDING: When a multi-hop CLEAR receipt chain is evaluated inside an external Verdict Record ([I-D.wright-verdict-record]), the rule checker MUST extract composite_window_end_ms, target_purdue_zone, and parent_node_hash directly from the digest-verified hop receipt bytes rather than trusting copied summary fields in the Verdict Record body.¶

6. Implementation Status and Empirical Benchmark Evaluation

The transitive CLEAR DAG revocation protocol and Purdue Level 0-2 physical-safety firewall specified in this document have been implemented and benchmarked across open-source governance suites:¶

• Open-Source Delegation & Kill-Switch Verifiers: Multi-hop delegation link verification, kill-switch signature validation, and scope-attenuation assertions are implemented across agentrust-io/trace-spec, agentrust-io/cmcp, OWASP/Agent-Security-Regression-Harness, and GenAI-Security-Project/GenAI-Agent-Security-Initiative ([AGENTIC-GOV-BENCHMARKS]).¶
• Core Rust Evidence Engine: Deterministic RFC 8785 JCS trace evidence reporting and monotonic confidence bounds are merged in xerj-org/xerj (engine/crates/xerj-common/src/hub_evidence.rs, [XERJ-HUB-EVIDENCE]).¶
• Empirical Benchmark Results: Evaluated across 100 contested multi-agent trials in the OWASP ASI01-ASI10 benchmark ([OWASP-ASI-BENCHMARK-DOI]) and the companion Technical Report ([ZENODO-TR-2026-03]), cycle-safe transitive CLEAR revocation halts downstream child and grandchild branches within a single heartbeat window and achieves 0.0% unauthorized writes across Purdue Level 0-2 PLC/SIS boundaries.¶

7. Security Considerations

All pre-image objects MUST be canonicalized using RFC 8785 JSON Canonicalization Scheme (JCS) prior to signature generation or verification under RFC 8032 Ed25519. Any clock skew exceeding 60 seconds, digest mismatch, or missing cryptographic binding MUST cause the verifier to fail closed and emit an auditable security rejection receipt. For the normative test vector in Section 3, the Ed25519 test key seed is 2a2a...2a (32 bytes of 0x2a), yielding raw 32-byte public key 197f6b23e16c8532c6abc838facd5ea789be0c76b2920334039bfa8b3d368d61 (kid = sha256:b600306cfa76723fdec395e53a9b3d9fdb78b1e2d7a23c32fcbcd2dc6d0c4092), and the full RFC 8785 JCS-canonicalized envelope (620 bytes) hashes to SHA-256 efc24ed02692c73f33560c5f91924dedb24da33dfcbd2f02eba6960d2f4119fa. This specification cross-references the companion Internet-Drafts ([I-D.durga-agenttrust-trace-verification], [I-D.durga-wimse-ctx-isolation], [I-D.durga-pquip-pqc-agentic-delegation], [I-D.durga-agent-tx-compensation-lease]), external Verdict Record evidence binding ([I-D.wright-verdict-record]), Remote Attestation ([RFC9334]), Merkle Tree domain separation ([RFC9162]), and the 100-scenario OWASP ASI01-ASI10 benchmark ([OWASP-ASI-BENCHMARK-DOI]).¶

8. IANA Considerations

This document requests IANA registration of the media type application/agent-clear-dag+json and the registry IETF Agent Industrial Purdue Zone Identifiers (PERA_LEVEL_0_PROCESS through PERA_LEVEL_5_ENTERPRISE), alongside the following header fields:¶

• HTTP/MCP Header Field: Agent-Clear-DAG¶
• HTTP/MCP Header Field: Agent-OT-Zone-Assertion¶

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