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vsa attestor

Typed decoder for pre-signed SLSA VSA predicates so downstream policies can consume external VSAs as first-class attestations — distinct from policyverify, which produces a VSA at verify time.

Namevsa
Predicate typehttps://slsa.dev/verification_summary/v1
Lifecycleverify
Default binary?No — builder opt-in only

What it captures​

The attestor wraps a VerificationSummary predicate that mirrors the SLSA VSA v1 shape. Its MarshalJSON emits the embedded predicate directly so Rego sees input.verifier.id, input.verificationResult, etc.

Fields on VerificationSummary:

  • verifier — { id string } identifying the party that ran verification.
  • timeVerified — wall-clock timestamp the source VSA was produced.
  • policy — ResourceDescriptor (uri, digest) referencing the policy that was evaluated.
  • inputAttestations[] — ResourceDescriptor entries (uri, digest) for each attestation considered.
  • verificationResult — "PASSED" or "FAILED" (the only two values defined in the package).

ResourceDescriptor shape: { uri string, digest cryptoutil.DigestSet }.

When to use​

Build this attestor in when a downstream policy needs to read a VSA that was produced outside the current pipeline — for example, a deploy gate that ingests a release pipeline's signed VSA as an external attestation, then re-asserts policy on top of it. The factory is looked up via FactoryByType on the predicate URI and decodes the bare DSSE payload into the typed shape.

Contrast with policyverify: policyverify runs inside cilock verify and emits a fresh VSA recording the outcome of that verify run. vsa does the inverse — it has a no-op Attest() and exists purely so a pre-signed VSA predicate can be unmarshalled and exposed to Rego under canonical SLSA field names.

Flags​

None. The attestor has no flag surface; it is selected by predicate-type lookup, not by name on the CLI.

Output shape​

{
  "verifier": { "id": "..." },
  "timeVerified": "2026-05-21T12:34:56Z",
  "policy": {
    "uri": "...",
    "digest": { "sha256": "..." }
  },
  "inputAttestations": [
    { "uri": "...", "digest": { "sha256": "..." } }
  ],
  "verificationResult": "PASSED"
}

Gotchas​

  • Verify-only. RunType is attestation.VerifyRunType. The factory is not selectable inside cilock run and Attest() is a no-op — it never produces an attestation by itself.
  • Decoder, not emitter. To emit a VSA from a verify run, use policyverify. The vsa package exists so external VSAs can flow into downstream policies as typed input.
  • PredicateType is the only routing key. Registration uses the SLSA VSA v1 URI; bare-predicate DSSEs with any other type will not be routed to this factory.
  • Field names match the SLSA spec, not the wrapper. Custom MarshalJSON/UnmarshalJSON flatten the embedded Predicate field out of the JSON, so policies should reference verifier, verificationResult, etc. directly — not predicate.verifier.

CLI example​

See the constraint summary + reproduction recipe at https://github.com/aflock-ai/attestor-compliance-examples/tree/main/42-vsa. This attestor is currently blocked or doc-only — the linked example explains why and shows the recipe to validate once the constraint is removed.

See also​