Verify a release artifact

Download the selected platform archive, its .sha256, .sig and .pem files, and the signed SBOMs from the same release. The checked-in release workflow builds archives, publishes checksums, and signs archives and per-binary CycloneDX SBOMs with cosign. Check the workflow at the selected tag before assuming a historical release has the same evidence.

Examples below use the v0.6.0 Linux x86-64 archive. Run them in the download directory, substituting your exact version/platform filenames.

1. Checksum

shasum -a 256 -c opaque-0.6.0-x86_64-unknown-linux-gnu.tar.gz.sha256

A match checks file integrity against the published digest. It does not identify the producer. Stop on a mismatch.

2. Sigstore signature (tarball and SBOM)

Releases are signed keylessly with cosign, using the GitHub Actions OIDC identity of the release.yml workflow rather than a long-lived private key. Verify the tarball:

cosign verify-blob \
  --certificate opaque-0.6.0-x86_64-unknown-linux-gnu.tar.gz.pem \
  --signature   opaque-0.6.0-x86_64-unknown-linux-gnu.tar.gz.sig \
  --certificate-identity-regexp 'https://github\.com/(kcirtapfromspace|opaque-dev)/opaque/\.github/workflows/release\.yml@.*' \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com \
  opaque-0.6.0-x86_64-unknown-linux-gnu.tar.gz

Releases up to and including v0.4.0 were signed before the repository moved to the opaque-dev organization, so their certificates name kcirtapfromspace/opaque; later releases name opaque-dev/opaque. The pattern above accepts exactly those two owners and nothing else.

Verify the CycloneDX SBOM the same way, pointing at its own .sig/.pem pair:

cosign verify-blob \
  --certificate opaque-0.6.0-opaque.cdx.json.pem \
  --signature   opaque-0.6.0-opaque.cdx.json.sig \
  --certificate-identity-regexp 'https://github\.com/(kcirtapfromspace|opaque-dev)/opaque/\.github/workflows/release\.yml@.*' \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com \
  opaque-0.6.0-opaque.cdx.json

A valid signature binds the bytes to the accepted workflow identity. Inspect the certificate identity and expected release tag; it does not establish safe code or complete build-input provenance. See the Sigstore verification reference for certificate/signature and bundle formats.

Evidence not supplied by the current workflow

The checked-in workflow uses cargo build, not cargo auditable build, and has no actions/attest-build-provenance step. Helper scripts and proposed procedures do not establish an embedded dependency manifest or SLSA provenance for an existing binary. Do not treat absent evidence as successful verification.

Evidence	What to inspect
Checksum	Download bytes match the published digest
Cosign signature	Bytes match an accepted repository/workflow signing identity
Signed SBOM	The signer supplied this dependency inventory; compare it with the selected build
Source and tests	Implementation and test evidence for the chosen operation

These checks do not establish reproducible builds, a trustworthy runtime host, regulatory certification or customer operating effectiveness. Continue with deployment verification before granting broker custody.