Cryptographic Context Compaction Receipts, Sensitivity Label Inheritance, and Verifiable Right-to-Be-Forgotten Lineage for Agent Memory

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Table of Contents

1. Introduction and Problem Statement

When an agent summarizes 50 conversational turns and 12 retrieved enterprise files into a single compacted memory embedding or summary node, existing provenance formats (W3C PROV, SCITT) lose the cryptographic link between the pre-compaction source digests and the post-compaction memory artifact. Consequently, a HIGHLY_CONFIDENTIAL document can be silently laundered into an unlabeled memory summary, or survive a mandatory regulatory deletion tombstone.¶

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 Ephemeral Compaction & Privacy Lineage.¶

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. Ephemeral Context Compaction Receipt (ECCR) Format

Whenever an agent memory subsystem performs lossy summarization, KV-cache eviction, or episodic memory compaction, it MUST emit a signed ECCR object before persisting the compacted artifact:¶

{
  "eccr_version": "1.0",
  "compaction_event_id": "urn:uuid:11a92c44-88b1-42c0-991a-77651234abcd",
  "source_items_merkle_root": "sha256:1b4f0e9851971998e732078544c96b36c3d01cedf7caa332359d6f1d83567014",
  "source_item_count": 62,
  "compacted_output_hash": "sha256:7d865e959b2466918c9863afca942d0fb89d7c9ac0c99bafc3749504ded97730",
  "inherited_sensitivity_ceiling": "CONFIDENTIAL_RESTRICTED",
  "retention_purge_epoch": 1796083200,
  "tombstone_bloom_filter_b64": "base64url_bloom_8B_A8f3_91b0",
  "signature": {
    "alg": "Ed25519",
    "kid": "sha256:b600306cfa76723fdec395e53a9b3d9fdb78b1e2d7a23c32fcbcd2dc6d0c4092",
    "sig": "1T9G-F9eEdNTpngEMpZj2P84k649jwESn8VEUuxbRAlHB1Ik9bIqgqfjPfKoJksgKr4UmvAadS_3e5w0UvmqDg"
  }
}

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. LEAST_UPPER_BOUND_LABEL_INHERITANCE: The inherited_sensitivity_ceiling of a compacted memory artifact MUST equal the strict least-upper-bound (maximum sensitivity dominance level) of all pre-compaction source items included in source_items_merkle_root.¶
2. CRYPTOGRAPHIC_TOMBSTONE_PROPAGATION: If any source item included in source_items_merkle_root receives a regulatory purge tombstone, the memory store MUST invalidate compacted_output_hash and re-compact over the remaining non-tombstoned leaves, emitting a new superseding ECCR.¶
3. RETENTION_CEILING_BINDING: The retention_purge_epoch of the compacted artifact MUST NOT exceed the minimum expiration timestamp among all contributing source items.¶

5. Strict Parser Determinism and Wire-Level Input Hardening

Memory compaction pipelines process untrusted conversational turns and external documents that may attempt to smuggle malformed JSON/Unicode payloads into long-term vector or graph stores. Conforming ECCR emitters and verifiers MUST enforce five pre-canonicalization parser invariants:¶

1. DUPLICATE_KEY_REJECTION: The JSON parser MUST reject any ECCR envelope containing duplicate keys (such as duplicate inherited_sensitivity_ceiling or retention_purge_epoch members) at parse time so a lower sensitivity label cannot overwrite a higher label during deserialization.¶
2. IEEE754_FINITE_SAFE_INTEGER_BOUNDS: Both source_item_count and retention_purge_epoch MUST be exact JSON integers within [1, 2^53 - 1]. Boolean values, floating-point timestamps, pre-epoch negative numbers, and non-finite constants (NaN, Infinity, 1e1000) MUST be rejected.¶
3. STRICT_SENSITIVITY_LATTICE_ENUMERATION: The inherited_sensitivity_ceiling MUST match a registered, uppercase ASCII lattice identifier with no leading/trailing whitespace or control characters, and unknown or unmapped classification tiers MUST fail closed to the highest restricted ceiling.¶
4. CANONICAL_HEX_AND_MERKLE_PROOF_BINDING: Both source_items_merkle_root and compacted_output_hash MUST match ^sha256:[0-9a-f]{64}$, and any accompanying RFC 9162 inclusion proof MUST bind tree_size to the exact source_item_count.¶
5. EVIDENCE_TO_RULE_BYTE_BINDING: When an ECCR receipt is cited inside an external Verdict Record ([I-D.wright-verdict-record]) to prove regulatory erasure or DLP compliance, the rule evaluation MUST read inherited_sensitivity_ceiling and retention_purge_epoch directly from the digest-verified ECCR bytes.¶

6. Implementation Status and Empirical Benchmark Evaluation

The Ephemeral Context Compaction Receipt (ECCR) protocol and sensitivity-ceiling inheritance rules specified in this document have been implemented and validated across open-source telemetry and security regression suites:¶

• Open-Source Memory & Telemetry Verifiers: Data-flow classification tier validation, tuple privacy-bypass prevention, bounded encoding-ladder memory isolation assertions, and Merkle tree-size binding are implemented across agentrust-io/agentrust-telemetry, agentrust-io/trace-registry, agentrust-io/weight-custody-manifest, and OWASP/Agent-Security-Regression-Harness ([AGENTIC-GOV-BENCHMARKS]).¶
• Core Rust Evidence Engine: Deterministic RFC 8785 JCS evidence digesting (TraceEvidenceReport) and pinned citation verification are implemented in Rust in xerj-org/xerj (engine/crates/xerj-common/src/hub_evidence.rs, [XERJ-HUB-EVIDENCE]).¶
• Empirical Benchmark Results: Evaluated against the 100-scenario OWASP ASI01-ASI10 Enterprise Agentic AI Security Regression Benchmark ([OWASP-ASI-BENCHMARK-DOI]) and the companion Technical Report ([ZENODO-TR-2026-04]), ECCR least-upper-bound label inheritance and cryptographic tombstone propagation prevent 100% of cross-compaction sensitivity-label laundering and verify GDPR Article 17 erasure lineage deterministically.¶

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 (672 bytes) hashes to SHA-256 fb90df742a9b5bb44e844884790f042c334e881a0b04320fa842e0d652b33d9f. 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-lineage-eccr+json and the registry IETF Agent Memory Sensitivity Ceiling Profiles, alongside the following header fields:¶

• HTTP/MCP Header Field: Agent-Memory-Lineage-Receipt¶

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