Attach and verify a cosign attestation for an SBOM linked to a container image
domain: docs.sigstore.dev · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Generate the SBOM (e.g. with Syft) as sbom.json, then attach it as an attestation: `cosign attest --predicate sbom.json --type spdxjson <IMAGE>` (use `--type cyclonedx` for a CycloneDX SBOM), signing with `--key cosign.key` for a static key or omitting --key for keyless signing via Fulcio + Rekor.
For keyless signing in CI, grant the workflow `permissions: id-token: write` so cosign can obtain an ambient OIDC token (cosign auto-detects the github-actions provider), or pass one explicitly with --identity-token.
Verify the attestation against the transparency log: `cosign verify-attestation --type spdxjson --certificate-identity <EXPECTED_IDENTITY_OR_REGEXP> --certificate-oidc-issuer https://token.actions.githubusercontent.com <IMAGE>` for keyless, or `cosign verify-attestation --type spdxjson --key cosign.pub <IMAGE>` for key-based verification.
Inspect the verified predicate contents with `cosign verify-attestation ... <IMAGE> | jq -r .payload | base64 -d | jq .predicate`.
Optionally enforce policy on the predicate with `--policy <FILE>.rego` or `--policy <FILE>.cue` passed to verify-attestation.
Known gotchas
Keyless verification requires either --certificate-identity or --certificate-identity-regexp, AND either --certificate-oidc-issuer or --certificate-oidc-issuer-regexp — omitting either pair fails verification even though the underlying signature is valid.
--type must match on both sides: an attestation created with --type spdxjson is not matched by verify-attestation run with the default --type custom (or any other mismatched predicate type).
Sigstore's own docs caution against using the dedicated SBOM predicate types (spdx/spdxjson/cyclonedx) for large SBOMs, since the entire SBOM gets embedded in the signature bundle and must be downloaded whenever the attestation is verified.
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