Sigstore

Sigstore eliminates the need for developers to manually generate, store, and rotate private keys. Instead, it binds a short-lived ephemeral signing certificate to an OpenID Connect (OIDC) identity token from platforms like Google, GitHub, or Microsoft.

• The client authenticates via OIDC to prove their identity.
• A Certificate Authority (Fulcio) issues a code-signing certificate valid for only 10 minutes.
• The private key is generated in-memory and discarded immediately after signing, preventing exfiltration.

Every signature is recorded in an immutable, append-only Merkle tree-based transparency log called Rekor. This provides a publicly auditable record of all signing events.

• Cryptographic proof of inclusion is generated for every entry.
• Monitors can detect anomalous signing activity, such as a compromised CI/CD pipeline.
• Enables verification of artifacts long after the ephemeral certificate has expired, ensuring non-repudiation.

The Cosign CLI tool provides a seamless interface for both signing and verifying artifacts against the Sigstore public good instance. Verification is policy-driven and can be integrated directly into Kubernetes admission controllers.

• Verify signatures using cosign verify with a simple image reference.
• Enforce keyless signing policies by checking the OIDC issuer and subject identity embedded in the certificate.
• Integrate with Binary Authorization to prevent unsigned or untrusted images from running in production.

Sigstore extends beyond artifact signing to cryptographically attest to the Software Bill of Materials (SBOM) associated with a container image. This binds the provenance metadata directly to the artifact.

• Cosign can attach and sign SPDX or CycloneDX SBOMs to images.
• Verifiers can confirm that the SBOM was generated by a trusted builder and hasn't been tampered with.
• This closes a critical gap in supply chain security, linking the artifact to its declared composition.

The Trust Root establishes the chain of trust for the entire ecosystem. It is a public, verifiable configuration that pins the identities of the Fulcio CA and the Rekor transparency log.

• Clients perform TUF (The Update Framework)-based secure bootstrapping to fetch the current Trust Root.
• This prevents rollback attacks and ensures all participants agree on the valid signing authorities.
• The Trust Root is managed transparently, with changes requiring community consensus and a recorded history.

To provide long-term validity even if underlying cryptographic algorithms are weakened, Sigstore supports RFC 3161 compliant timestamping. A Timestamp Authority (TSA) issues a signed timestamp proving the signature existed before certificate expiry.

• The timestamp is countersigned and embedded in the Rekor log entry.
• This provides cryptographic proof of existence at a specific point in time.
• Combined with the transparency log, it enables verification decades into the future, independent of the original CA.

A formal, machine-readable inventory of all components, libraries, and dependencies that constitute a software artifact. SBOMs enable vulnerability tracking and license compliance by providing a transparent manifest of what's inside a package.

• SPDX and CycloneDX are the dominant SBOM formats
• Sigstore signatures can attest to the authenticity of an SBOM itself
• Combined with signing, SBOMs provide both provenance and composition visibility

Supply-chain Levels for Software Artifacts provides a graduated checklist of controls to prevent tampering and improve integrity throughout the build and distribution process. SLSA Level 3 requires non-falsifiable provenance.

• Defines four ascending levels of security maturity
• Level 2 requires signed provenance from a hosted build platform
• Sigstore's keyless signing aligns directly with SLSA provenance generation requirements

A metadata specification that cryptographically verifies the steps and materials used in a software supply chain. In-toto attestations provide non-repudiable evidence of the build process integrity by capturing the full chain of custody.

• Uses predicate types to define what is being attested (e.g., SLSA provenance)
• Sigstore's Cosign tool natively generates and verifies in-toto attestations
• Enables policy enforcement based on cryptographically verified build steps

A deploy-time security control that enforces signature validation, ensuring only trusted and verified container images are allowed to run in a production environment. Binary Authorization acts as the enforcement point for Sigstore signatures.

• Integrates with Kubernetes admission controllers
• Validates Cosign signatures before allowing pod creation
• Prevents deployment of unsigned or untrusted artifacts at the policy enforcement point

Verifiable information about the origin, build steps, and source materials that produced a specific software artifact. Provenance allows consumers to assess trustworthiness by answering 'who built this, from what, and how?'

• Captures build platform identity, source repository, and build commands
• Sigstore enables non-repudiable provenance through ephemeral key signing
• Forms the foundation for policy-based deployment decisions in zero-trust pipelines

A mechanism that allows a software workload running outside a cloud provider to securely impersonate a service account using an external identity token. This eliminates the need for long-lived service account keys.

• OIDC tokens from platforms like GitHub Actions serve as the identity source
• Sigstore's Fulcio certificate authority validates these tokens to issue short-lived signing certificates
• Enables keyless signing by binding artifact signatures to workload identities, not static keys