Sigstore

Cosign is the primary client for interacting with the Sigstore ecosystem. It signs and verifies OCI artifacts (container images, Helm charts, model weights) stored in standard registries. Verification is a three-step process:

1. Cryptographic Check: Validates the digital signature against the artifact's digest.
2. Certificate Check: Confirms the short-lived certificate was issued by the trusted Fulcio CA.
3. Transparency Check: Proves the signature entry exists in the Rekor log. This ensures the artifact is both intact and from a verified identity, all without distributing a public key.

The primary command-line interface for the Sigstore ecosystem. Cosign signs and verifies container images and other OCI artifacts using keyless signing workflows.

• Signs images with ephemeral keys bound to an OIDC identity
• Stores signatures directly in the container registry alongside the artifact
• Verifies signatures against the Rekor transparency log
• Supports signing blobs, SBOMs, and in-toto attestations

Example: cosign sign --fulcio-url=https://fulcio.sigstore.dev --rekor-url=https://rekor.sigstore.dev gcr.io/project/image:latest

The certificate authority within Sigstore that issues short-lived code-signing certificates. Fulcio authenticates users via OpenID Connect and binds their verified identity to an ephemeral X.509 certificate.

• Certificates are valid for only 10 minutes, eliminating long-term key management
• Supports OIDC providers including Google, GitHub, and Microsoft
• The certificate embeds the signer's verified email or workload identity
• No private key is ever stored or transmitted—keys are generated and discarded in-memory

The immutable transparency log that records every signing event in Sigstore. Rekor provides an append-only, cryptographically verifiable ledger that makes the signing process publicly auditable.

• Prevents retroactive forgery—once logged, a signature cannot be denied
• Stores signed metadata including the certificate, signature, and artifact hash
• Enables monitoring for unauthorized or unexpected signing events
• Built on the Merkle tree data structure for efficient cryptographic proofs of inclusion

A paradigm shift from managing long-lived private keys to binding signatures to workload identities. Keyless signing uses OIDC tokens to authenticate the signer, then Fulcio issues an ephemeral certificate.

• Eliminates the risk of private key theft, loss, or mismanagement
• The signing key is generated in-memory and destroyed immediately after use
• Identity is rooted in the OIDC provider's authentication, not a stored secret
• Critical for automated CI/CD pipelines where manual key distribution is impractical

A framework for cryptographically attesting to each step in a software supply chain. When combined with Sigstore, in-toto attestations are signed using keyless identities and recorded in Rekor.

• Defines the SLSA provenance predicate for describing how an artifact was built
• Attestations can capture build parameters, source repositories, and builder identity
• Enables policy-based verification—only artifacts with specific attestations are admitted
• Cosign natively supports creating and verifying in-toto attestations via cosign attest

A deploy-time enforcement mechanism that ensures only verified, signed artifacts run in production. Binary Authorization integrates with Sigstore signatures to create a policy gate at the admission controller level.

• Validates that images are signed by trusted identities before Kubernetes schedules pods
• Can require specific attestations such as vulnerability scan results or SLSA provenance
• Prevents deployment of unsigned or untrusted artifacts even if they exist in the registry
• Implemented via OPA or cloud-native admission controllers like Google Cloud Binary Authorization