Sigstore
An open signing ecosystem that issues short-lived certificates bound to an OIDC identity and records every signature in a public transparency log.
Sigstore has three parts. cosign signs and verifies container images and blobs. Fulcio is a CA that, after an OIDC login (a human, or a CI workload such as GitHub Actions), issues a certificate valid for about ten minutes that binds the signing key to that identity. Rekor is an append-only transparency log that records the signature so it can be verified after the certificate expires.
It removes the hardest part of signing: managing long-lived private keys. "Keyless" means the key is ephemeral and identity comes from your IdP or CI, so the policy you verify is "signed by workflow X in repo Y".
The common mistake is verifying that a signature exists without pinning the identity and issuer: any GitHub user can produce a valid Sigstore signature. Always verify --certificate-identity and --certificate-oidc-issuer, and enforce it at admission.
cosign verify ghcr.io/acme/api@sha256:3f1c... \
--certificate-identity "https://github.com/acme/api/.github/workflows/release.yml@refs/heads/main" \
--certificate-oidc-issuer "https://token.actions.githubusercontent.com"