cosign attest: Attach an SBOM Attestation

cosign attest signs an attestation (such as an SBOM or build provenance) and attaches it to a container image.

A signature says who built an image; an attestation says what is inside it or how it was made. cosign attest binds a signed predicate, often an SBOM, to the image digest.

What it does

cosign attest wraps a predicate file (an SBOM, SLSA provenance, or custom JSON) in an in-toto attestation, signs it (key-based or keyless), and stores it next to the image. cosign verify-attestation later checks the signature and the predicate type, optionally evaluating a policy against the predicate.

Common usage

Terminal

# attach a CycloneDX SBOM attestation, keyless
syft ghcr.io/org/app@${DIGEST} -o cyclonedx-json=sbom.cdx.json
cosign attest --yes --type cyclonedx \
  --predicate sbom.cdx.json ghcr.io/org/app@${DIGEST}
# verify the attestation by identity
cosign verify-attestation --type cyclonedx \
  --certificate-identity-regexp 'https://github.com/org/.+' \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com \
  ghcr.io/org/app@${DIGEST}

Options

Flag	What it does
--predicate <file>	The predicate JSON (SBOM, provenance, custom)
--type <type>	Predicate type: cyclonedx, spdxjson, slsaprovenance, custom
--key <ref>	Signing key (omit for keyless)
--yes	Skip the confirmation prompt
--policy <file>	CUE/Rego policy for verify-attestation

In CI

Generate the SBOM with syft or trivy, then cosign attest --type cyclonedx (or spdxjson) keylessly so the SBOM is signed and stored with the image. Verify it in the deploy gate with cosign verify-attestation, pinning the same identity and issuer used at build time.

Common errors in CI

"invalid predicate type" means --type does not match the predicate format; use cyclonedx for CycloneDX and spdxjson for SPDX. "no matching attestations" on verify means the type filter differs from what was attached, or you verified a moved tag. EOF on the password prompt means COSIGN_PASSWORD is unset for a key-based attest.