Sigstore
Open-source software supply chain security project
Sigstore is an open-source project that provides free tooling for signing, verifying, and recording provenance of software artifacts, aiming to make cryptographic signing of code and container images as easy as signing in with an existing…
Definition
Sigstore is an open-source project that provides free tooling for signing, verifying, and recording provenance of software artifacts, aiming to make cryptographic signing of code and container images as easy as signing in with an existing identity provider. It removes the traditional burden of managing long-lived private signing keys by issuing short-lived certificates tied to an OpenID Connect identity and publishing every signature to a public, tamper-evident transparency log.
Overview
Verifying that a piece of software actually came from the party who claims to have published it, and that it hasn't been tampered with since, is a foundational software supply chain security problem. Traditional code signing solves part of this with public-key cryptography, but it requires developers and organizations to generate, protect, and rotate long-lived private keys, a burden significant enough that many open-source projects historically skipped signing altogether. Sigstore was created to remove that barrier by making signing free, automated, and keyless. Mechanically, Sigstore's core components work together: Fulcio acts as a certificate authority that issues short-lived X.509 certificates after a signer proves their identity through an OpenID Connect provider, such as a GitHub or Google login, rather than presenting a pre-existing key. Rekor, a public transparency log, records every signing event immutably, so anyone can later verify that a specific artifact was signed by a specific identity at a specific time, and detect if a log entry were ever altered. Because the signing certificate expires quickly, there is no long-lived key to steal or leak; the transparency log provides the durable record instead. Sigstore's approach differs from traditional PKI-based code signing, such as Docker Content Trust or Notary, which rely on developers managing their own persistent key pairs and infrastructure. It also differs from artifact-scanning tools like Grype or Syft, which examine what is inside an artifact rather than proving who published it; these are complementary pieces of a supply chain security stack. Cosign, built on Sigstore, is the most common client tool for actually signing and verifying container images and other artifacts using the Sigstore infrastructure. In practice, open-source projects and companies use Cosign inside CI/CD pipelines to automatically sign container images and release artifacts as part of the build process, with no manual key handling required. Downstream consumers, including Kubernetes admission controllers, can then enforce a policy that only artifacts signed by a trusted identity and recorded in Rekor's transparency log are allowed to run, closing a gap that let unsigned or tampered artifacts through unnoticed in many pipelines. Because Sigstore's public infrastructure is a shared, internet-facing service, it introduces a dependency on Sigstore's own availability and on trust in the OpenID Connect identity providers used for signing; an organization with especially strict air-gapped requirements may need to run private instances of Fulcio and Rekor instead of the public good service. Verification policies must also be configured deliberately, since simply having a signature proves identity and integrity at signing time but does not, by itself, guarantee an artifact is free of vulnerabilities.
Key Features
- Keyless signing using short-lived certificates tied to OpenID Connect identity
- Fulcio certificate authority issues ephemeral signing certificates automatically
- Rekor transparency log provides a public, tamper-evident record of signatures
- Cosign client tool signs and verifies container images and artifacts
- Removes the need for developers to manage long-lived private signing keys
- Integrates into CI/CD pipelines for automated release signing
- Supports policy enforcement that only trusted signed artifacts can deploy
- Free, publicly hosted infrastructure backed by the Open Source Security Foundation