Sigstore

How it works

Sigstore is a set of services for signing software artifacts without managing long-lived private keys. Its signing tool, cosign, obtains an OIDC token representing an identity (typically the workflow identity of a CI job), receives a short-lived certificate from the Fulcio certificate authority, signs the artifact, and records the certificate and signature in the Rekor transparency log. The certificate expires within minutes. Verification checks the signature, confirms the certificate chains to Fulcio, and confirms the entry exists in the log, which establishes that the signature was created while the certificate was valid.

When it matters

It matters wherever artifact signing previously stalled on key custody, which is nearly everywhere: keyless signing removes the private key nobody wanted to own, rotate, or protect. It is the signing layer underneath most SLSA provenance workflows. Sigstore proves who signed; SLSA provenance describes how the artifact was built. Both are needed. See Verified Builds with SLSA and Sigstore.

Common misconceptions

• "Keyless means no cryptography." Keys are still used. They are ephemeral and bound to a verified identity rather than stored.
• "A valid signature means the artifact is safe." It means a specific identity signed it. If your policy does not constrain which identities and source repositories are acceptable, it accepts anything anyone has signed.
• "The transparency log is optional." Verification that silently proceeds when the log is unreachable turns a network failure into a security bypass.