SLSA Verifier

A command-line verifier for SLSA attestations: build provenance (build), source provenance (source) and Verification Summary Attestations (vsa). It parses plain in-toto statements, DSSE envelopes and Sigstore bundles, verifies their signatures when asked to, evaluates the SLSA controls for the requested track and level, and can emit a VSA from the result.

# Verify build provenance
slsa-verifier build  --require-signatures --signer <spec> --level 3 provenance.sigstore.json

# Verify source provenance
slsa-verifier source --official --level 3 --expected-branch refs/heads/main source-provenance.sigstore.json

# Verify a VSA
slsa-verifier vsa --verifier 'https://verify.example.com=<signer spec>' --level SLSA_BUILD_LEVEL_3 vsa.sigstore.json

Every subcommand prints PASS or FAIL with the per-control roster and exits with 0 on pass, 1 on a verification failure and 2 when the verification could not run (bad flags, unreadable input, missing key material). Run any subcommand with --help for its flags and examples.

Trust model

Read this before relying on the tool's output. The defaults are deliberately permissive so that attestations can be inspected without any key material, making a result trustworthy requires opting in.

• Signatures are not required by default, but a refuted one always fails. Without --require-signatures, an unsigned statement, or a signed one whose signature could not be checked, is evaluated on its content alone (and the result says so). A signature that was checked and did not verify fails the run regardless: unsigned means no claim of integrity, refuted means a claim of integrity that is false. With it, the statement must carry a signature that verified: a missing one fails the run, and a signed statement with nothing to verify it against (no --key for a key-signed DSSE envelope) is refused rather than passed. Legacy keyless envelopes (DSSE signed with a Sigstore certificate) are verified against the Rekor transparency log by default (--rekor-url names the instance) with no network they stay uncheckable and the run degrades as above.
• Who signed is not checked unless you say who you expect. A verified signature proves the content is intact, not that the right party produced it. Use --signer <spec> (all subcommands), --official (source, the official SLSA source workflow identity) or a per-verifier binding --verifier <id>=<spec> (vsa) to require a specific identity. Any of these implies --require-signatures.
• Claims inside an attestation are claims. builder.id, verifier.id and the controls a source provenance lists are written by whoever produced the document. Claims only mean something once the signer is bound to them: for vsa the tool refuses a verifier bound to no signer with --verifier <id>=<spec>, a registry file passed with --verifiers, or a wildcard --signer (unless you pass --allow-unbound-verifier). For build, a signed attestation's builder.id is bound to its signer through the builder registry and a builder nothing binds is reported unproven. For source, pass a signer.
• The VSA it emits summarizes what it checked. A VSA emitted with --vsa from an unsigned or unbound input is a summary of an unverified document. Only issue VSAs from runs that required and bound signatures.

See SECURITY.md for how to report a problem.

Builder registry

A signed build attestation's builder.id is proven, not just checked, by binding it to the identity that signed the statement.

The verifier ships a registry of builders and their signers and reports the binding as the builder-identity-bound control. Builders of your own can be bound with --builder <id>=<signer spec>, with a registry file passed with --builders, or by naming the signer you expect with --signer.

A signed attestation naming a builder nothing binds still verifies, with builder.id reported unproven.

docs/builder-registry.md describes the rules, the file format and the embedded entries. VSA verifiers are bound the same way with --verifier <id>=<spec> or a registry file passed with --verifiers (see docs/verifier-registry.md.)

Currently, the registry ships with the slsa-github-generator builders and the GitHub Actions checks.

Development

go build ./...
go test -race ./...
golangci-lint run ./...

(Test fixtures live under pkg/slsa/testdata see its README.)