The Sectum AI evidence chain

Every Sectum AI run produces an evidence pack an auditor or DPO accepts. The pack is tamper-evident: anyone with the OSS sectum-ai verify can independently confirm that the pack was produced at a stated time, against stated test conditions, and has not been altered since.

Goals

Every run produces an EvidencePack with a stable schema, versioned for forward compatibility.
The pack is tamper-evident: mutating any field breaks verification with a specific [FAIL] reason.
Verification is independent of Sectum AI, the verifier and its supporting code are Apache 2.0; no Sectum AI installation is required to check a pack the customer received.
Findings carry control mappings (SOC 2 CC6.x, ISO 27001 A.8.x, GDPR Art. 17/32, EU AI Act Art. 15, NIST AI RMF MEASURE 2.7, OWASP LLM08:2025) so auditor walkthroughs map directly.

Construction

The pack is built deterministically. The steps:

Canonicalize the run. The run record, run_id, started_at, finished_at, scenario_hash, manifest_hash, adapter_versions, probe_versions, the list of findings, is serialized as canonical JSON: sorted keys, fixed numeric precision, no floats where avoidable.
Hash the canonical run. SHA-256 over the canonical JSON yields the run_digest. This is the single value the rest of the chain anchors to.
Timestamp the digest. The run_digest is submitted to an RFC 3161 Time-Stamp Authority. The returned TSA token binds the digest to a public time. Development uses a free TSA; production deploys configure a pinned TSA (or the customer's preferred TSA, where the auditor wants control).
Record in a transparency log. The digest plus signature is recorded as a Sigstore Rekor transparency-log entry; the inclusion proof is stored in the pack. Keyless signing via OIDC is the default where available; the operator can also configure a private Rekor or a self-managed key.
Wrap as in-toto attestation. The canonical run goes into an in-toto Statement envelope (subject = run_digest, predicate = the run + control mappings) so the artifact slots into existing supply-chain attestation tooling.
Render the audit PDF. A human-readable PDF covers the executive summary, scope, methodology, per-finding detail with mapped controls, and instructions for the recipient to verify the pack independently.

What ships in a pack

File	Purpose
`evidence.json`	Machine-readable, schema-versioned evidence record. Loaded by `sectum-ai verify` to validate the chain.
`audit-pack.pdf`	Human-readable: executive summary, scope, methodology, per-finding evidence, control mappings, verification instructions.
`attestation.intoto.json`	The in-toto Statement envelope binding the run digest to the predicate.
TSA token (in-band)	RFC 3161 timestamp token over the run digest.
Rekor inclusion proof (in-band)	Log index, inclusion proof, signed entry timestamp. Optional, on by default for Sectum Cloud, opt-in for OSS local runs.

Independent verification

The verifier ships in the Apache 2.0 OSS. Anyone can run it:

pip install sectum-ai
sectum-ai verify evidence.json \
  --tsa-cert tsa-cert.pem \
  --tsa-root tsa-root.pem \
  [--rekor-key rekor.pem]

Exit codes follow the rest of the CLI: 0 verified, 4 verification failed. A failure prints a [FAIL] line that explains exactly which check broke (e.g., run_digest mismatch, TSA signature invalid, Rekor inclusion proof does not match).

Tamper-evidence in practice

The properties an auditor cares about:

Mutating any field in evidence.json changes the run_digest; the TSA-signed digest no longer matches; sectum-ai verify exits with [FAIL] run_digest mismatch.
Re-signing the digest with a different TSA breaks the TSA-certificate-chain check; sectum-ai verify exits with [FAIL] tsa signature invalid or [FAIL] tsa certificate chain.
Forging a Rekor inclusion proof requires control of a Rekor key pinned in the verify call. Public Rekor proofs are validated against the publicly-published Sigstore root.
The manifest hash in the evidence pack binds the test conditions to the run. Editing the manifest after the fact changes its hash; the pack's stored value no longer matches; verification fails.

The non-goal

Sectum AI verifies and attests. It does not remediate. Findings include remediation pointers, specific surface, specific marker count, but the change to the customer's stack belongs to the platform team. The evidence chain proves what was tested, what was found, and when. Fixing the findings is a separate motion.

Sample artifacts

Real sample evidence packs ship in the OSS repo: docs/samples/. Includes a sample evidence.json, audit-pack.pdf, and attestation.intoto.json the buyer's auditor can inspect before signing an engagement.