Verify a signed artifact offline against a Sigstore Rekor transparency log entry using a cosign bundle
domain: docs.sigstore.dev · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Sign the artifact with cosign sign-blob using the bundle output option and keyless (Fulcio-issued) signing so the bundle embeds the certificate, signature, and Rekor inclusion proof.
Distribute the bundle file alongside the artifact instead of relying on a live Rekor lookup at verification time.
Verify offline with cosign verify-blob, passing the bundle plus the expected certificate-identity and certificate-oidc-issuer values.
Confirm cosign validates the embedded signed timestamp against the ephemeral certificate's validity window and validates the transparency log inclusion proof within the bundle before trusting the signature.
Pin certificate-identity and certificate-oidc-issuer to exact expected values in automated verification scripts rather than wildcards, to prevent accepting signatures from an unintended identity.
Known gotchas
Offline bundle verification still requires trusted root material (e.g. via TUF) to validate the certificate chain and log signature — it is offline with respect to Rekor network lookups, not fully airgapped from all trust anchors.
Omitting the certificate-identity/certificate-oidc-issuer checks weakens verification to "signed by someone with any Fulcio cert," defeating the purpose of keyless verification.
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