Sigstore helps software teams sign artifacts and verify who signed them, using short-lived certificates tied to authenticated identities and a public transparency log. Its core tools are Cosign, Fulcio and Rekor; TUF distributes the trust material verifiers need. This makes signing easier to audit and reduces reliance on long-lived private keys, but it does not prove that a build was safe or prevent a compromised identity from signing malicious software.
How Sigstore signing works
In a keyless signing flow, Cosign creates an ephemeral key pair in memory and requests an identity token from an OpenID Connect (OIDC) provider. Fulcio uses that authenticated identity to issue a short-lived certificate binding the identity to the public key. Cosign signs the artifact, then records the signature and certificate in Rekor, Sigstore’s transparency log.
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When someone verifies the artifact, the verifier checks that the signature matches the artifact, that the certificate represents the expected identity, that the certificate chains to trusted Sigstore material, and that Rekor provides an inclusion proof for the record. The verifier must check the identity it expects—not merely that some valid signature exists.
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| Component | Role in the workflow | What it does not establish by itself |
|---|---|---|
| Cosign | Command-line client for signing and verifying containers and other artifacts, including through OCI registries. | That the signer’s build process was trustworthy. |
| Fulcio | Certificate authority that issues temporary certificates binding a public key to an authenticated identity. | That an authenticated identity or its account has not been compromised. |
| Rekor | Append-only transparency log and API for signed metadata, inclusion proofs and audit queries. | That every log entry is authorized or that someone will notice a suspicious one. |
| OIDC | Identity layer that supplies authenticated user, service-account or CI-workflow tokens. | That the identity provider or the token’s workload is uncompromised. |
| TUF | Framework used to distribute and protect Sigstore trust-root material, including Fulcio’s root CA certificate and Rekor’s public key. | That a particular artifact or publisher should be trusted. |
| Policy Controller | Kubernetes admission controller that can enforce which signed containers are permitted to run. | That a container’s build claims are true unless suitable policy and evidence are checked. |
Is keyless signing safer than managing signing keys?
It changes the security trade-off rather than making signing automatically safe. Traditional signing requires teams to protect, distribute, rotate and, when necessary, revoke long-lived private keys. Sigstore’s keyless model avoids keeping a persistent signing key in the ordinary workflow: it shifts more of the assurance burden to the OIDC identity, short-lived certificate, verification rules and transparency monitoring.
#1 Best Overall
| Decision area | Long-lived signing keys | Sigstore keyless approach |
|---|---|---|
| Identity model | Possession of the private key is central to signing. | An OIDC identity is bound to an ephemeral public key by a short-lived certificate. |
| Operational burden | Protect, distribute, rotate and revoke durable keys. | Secure the identity provider and workload; define verification policy and monitor transparency records. |
| Auditability | Depends on the key system and the records a team maintains. | Rekor records signatures for public auditability and offers inclusion proofs. |
| Infrastructure choice | Can use an organization’s own or custom key infrastructure. | Uses Sigstore services and trust-root distribution; organizations still need a plan for service outages and policy. |
Keyless signing is a useful fit when a CI system or developer identity can be authenticated reliably and verifiers can pin the expected issuer and workload identity. It is not automatically preferable for every environment: teams with existing key controls, constrained connectivity or requirements for self-managed infrastructure should compare those needs with Sigstore’s identity and service dependencies.
How to verify a container image with Cosign
Verification is not just a cryptographic check. Before accepting an image, decide which identity is allowed to publish it and which artifact digest is being promoted. Then verify the signature against that identity and the Sigstore trust material, and require the Rekor inclusion evidence. The exact Cosign command and options depend on the installed release and the identity provider; configure verification using the syntax documented for that release rather than copying an identity-blind example.
Rank #2
- Choose the artifact. Identify the container image by its immutable digest, not only by a mutable tag, so the object verified is the one later promoted or deployed.
- Specify the trusted signer. Record the expected OIDC issuer and the appropriate identity fields for the repository, workflow, subject or service account. Use the values that correspond to your publishing pipeline.
- Run Cosign verification. Verify the image signature and require the certificate identity and trust chain you selected. A successful signature check against an unexpected identity is not sufficient.
- Require transparency evidence. Check Rekor inclusion as part of verification, then retain the verification result with the release or deployment record.
- Apply the result before use. Reject or quarantine an image when its digest, signature, identity, trust chain or inclusion evidence fails policy; investigate rather than weakening the identity check to make verification pass.
Cosign supports OCI-registry integration, but the workflow also depends on the registry, the issuer and the verifier’s trust-root configuration. Confirm those dependencies in the deployment environment, especially where builds or deployments run without reliable access to public services.
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A valid signature establishes that the artifact bytes match what was signed and, when verification checks the certificate identity, that the signature is associated with the expected identity under the chosen trust model. Rekor’s append-only, cryptographically verifiable design makes recorded signing activity auditable. These properties improve attribution and make some unauthorized activity detectable; they do not guarantee that every signing event was authorized or that someone will monitor the evidence.
- A compromised OIDC account or CI workload may be used to obtain a certificate and sign an artifact.
- Fulcio could issue an unauthorized certificate, or a failure involving Fulcio or Rekor could go unnoticed without monitoring.
- A signature does not show that the source code was safe, dependencies were trustworthy, or the build environment was uncompromised.
- A transparency log supports detection and audit; it is not a substitute for access controls, incident response or a decision about which identities and artifacts are acceptable.
Teams should monitor Rekor and certificate-transparency records for unexpected identities or signatures, protect the identity provider and CI workflows, and document how to respond to OIDC, Fulcio or Rekor outages. Sigstore’s security model depends on treating verification policy and monitoring as operational controls, not optional extras.
Does Sigstore replace SBOMs or provenance?
No. A signature links an artifact to a signing identity; it does not describe how the artifact was built or list its components. A software bill of materials (SBOM) describes components in a software product, while provenance makes claims about its source and build process. Sigstore can sign artifacts such as SBOMs and binaries, and it can be used with in-toto attestations, but the evidence and policy still need to answer the questions a consumer cares about.
Rank #4
For build assurance, verify relevant attestations or provenance in addition to the artifact signature. Define what claims are required—such as the expected repository, workflow and build identity—and enforce those requirements before release or deployment. In Kubernetes, Policy Controller can apply admission rules to signed containers; a signature alone is not a complete admission policy.
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- Inventory trust decisions. List the release artifacts to protect, the identities allowed to publish them, and the environments that will verify them.
- Connect CI identity. Integrate Cosign signing into the CI workflow using an OIDC issuer and confirm which workload identity the certificate will represent.
- Set verification policy. Specify expected issuer, repository, workflow, subject and artifact digest as applicable. Avoid rules that accept any valid signature.
- Gate promotion and deployment. Verify signatures and Rekor inclusion before an artifact advances to a release or deployment environment.
- Add build evidence where needed. Require provenance or attestations for claims about source, dependencies or build steps; separately decide whether an SBOM is needed.
- Enforce at runtime where appropriate. For Kubernetes workloads, consider Policy Controller admission controls so policy is checked when containers are admitted.
- Monitor and prepare for incidents. Alert on unexpected identities or signatures and document fallback and response procedures for identity-provider, Fulcio or Rekor disruptions.
Adoption and scale: dated indicators
Sigstore Community’s July 2024 roadmap snapshot reported more than 101 million Rekor entries, more than 33,000 unique open-source projects, more than 21 million Fulcio short-lived certificates, and a 99.5% public-service availability SLO since general availability in October 2022. These are dated community figures, not a guarantee of present-day usage or future availability.
Best Value
A Sigstore Blog roundup published in October 2025 reported Sigstore-signed in-toto attestations for Homebrew (May 2024), PyPI (November 2024), Maven Central (January 2025) and NVIDIA NGC (July 2025), and reported Cosign v3 in October 2025. Those examples indicate ecosystem use at the dates stated; they do not establish that every package or artifact on those services is signed.
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