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Every verdict Sengol records is a signed, append-only record. The gate verdict and the audit record are the same object. There is no separate compliance log rebuilt after the fact.

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Three layers of protection

1

HMAC signature

The appliance signs each record’s canonical JSON (RFC 8785) with its HMAC key. Every field the record sets is signed, except a short list of fields that are unsigned by design.
2

Hash chain

Each record carries a sequence_number and the prev_hash of the record before it. Removing, inserting or reordering a record breaks the chain.
3

Ed25519 countersignature

A second, asymmetric signature. Anyone with the appliance’s public key can check it offline, without the HMAC key. Countersigning runs asynchronously, shortly after ingest.
Optionally, the appliance also anchors records to an RFC 3161 timestamp authority and a transparency log (SENGOL_EVIDENCE_ANCHOR=1).

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What a record contains

Export one agent’s records, then look at the first one:
The first record in a chain has an empty prev_hash. controlbook_id is None because the demo records were written without a ControlBook.

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Signed

  • The verdict of every evaluator: passed (true or false) and, on failure, a named failure_mode
  • Agent id and version, tenant, policies, and the ControlBook id and version when the record was written under one
  • A UTC timestamp, fixed at write time
  • reason_digest: a keyed digest of each evaluator’s free-text reason
  • evaluator_version and judge_model on each evaluator’s score, when the suite stamped them
  • sample_basis and environment, on records written by online scoring of live calls

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Not signed, by design

  • The free-text reason. It is stored separately so that a data-subject erasure can remove it. The record still verifies afterwards, and the reason reads back as ERASED.
  • hmac_signature and signing_backend, which describe the signature itself.
sengol-verify lists the unsigned fields it found in its field_coverage check.

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Record families

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What is not signed evidence

These write logs or labels, not signed records:
  • human review decisions
  • user and role administration, including break-glass sign-ins
  • ControlBook activation

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Verifying

  • Offline, by anyone: sengol-verify checks the canonical payload, the chain and the countersignatures.
  • Online, with appliance access: sengol audit verify --chain --agent-id <id> also checks every HMAC.
A chain proves the records present link together. It does not prove the pack is complete. Check the sequence range and the period, as shown in the auditor journey.