Cosign

## Editorial notes

Cosign is useful when Claude-adjacent teams need concrete supply-chain controls around agents, CLI releases, containers, SBOMs, model-serving images, MCP servers, and automation artifacts. It gives developers and agents a scriptable way to sign build outputs, verify downloaded tools, attach attestations, prove CI identity, and make promotion gates depend on artifact identity instead of naming convention alone.

This entry covers the open-source Cosign CLI from the Sigstore project. It is distinct from Syft, which generates SBOMs, and Grype, which scans artifacts and SBOMs for vulnerabilities. Cosign can sign or verify SBOMs and attestations produced by other tools, but this listing focuses on Cosign itself as the artifact signing, verification, and attestation tool.

## Source notes

- The official repository describes Cosign as code signing and transparency for containers and binaries.
- The official repository says Cosign signs OCI containers and other artifacts using Sigstore.
- The README says Cosign supports keyless signing through Sigstore's Fulcio certificate authority and Rekor transparency log.
- The README lists support for hardware and KMS signing, encrypted key pairs, container signing, container verification, storage in OCI registries, and bring-your-own PKI.
- The README says users should sign images by digest rather than by tag to avoid signing something unintended.
- The README describes keyless signing with OIDC, a short-lived certificate from Fulcio, Rekor transparency-log storage, and signature upload beside the image in the OCI registry.
- The README shows verification with expected certificate identity and OIDC issuer arguments, including regular-expression variants.
- The Cosign installation docs describe release binaries, Go install, Homebrew, Linux package paths, the official container image, GitHub Actions installation, and GitLab CI installation.
- The signing docs say keyless signing can use OIDC providers such as Google, GitHub, and Microsoft, while key-based signing can use local keys, cloud KMS, Vault, OpenBao, Kubernetes secrets, and PKCS11.
- The signing docs describe signatures, attestations, annotations, saved bundles, later upload with ORAS, OCI 1.1 referrers, signature discovery with `cosign tree`, and cleanup behavior with `cosign clean`.
- The verification docs show public-key, KMS, keyless, blob, multiple-image, local-image, custom-CA, attestation, annotation, bundle, and transparency-log verification workflows.
- The verification docs explain that Cosign payloads include digests and that claim checking validates the digest unless explicitly disabled.
- The Sigstore quickstart says Cosign signs and verifies blobs and containers and that bundles include signature, certificate, timestamp, and transparency-log inclusion metadata.
- The Sigstore quickstart describes Fulcio issuing a short-lived certificate after OIDC identity verification and Rekor recording the signing activity.
- The repository is `sigstore/cosign`, is Apache-2.0 licensed, active, and maintained under the Sigstore project.

## Duplicate check

Checked current `content/tools/`, `content/mcp/`, agents, hooks, rules, skills, commands, guides, collections, open pull requests, live issue state, and repository-wide content for `Cosign`, `Sigstore`, `sigstore/cosign`, `github.com/sigstore/cosign`, `docs.sigstore.dev/cosign`, `Fulcio`, `Rekor`, `keyless signing`, `container signing`, `artifact signing`, and `supply chain signing`. Existing content contains only incidental Cosign-compatible signing mentions inside the Syft tools entry; no dedicated Cosign tools entry, target file, exact source URL duplicate, issue duplicate, semantic duplicate, or open duplicate PR was found.

## Disclosure

Editorial listing. No paid placement or affiliate link is used. Cosign is Apache-2.0 open-source software under the Sigstore project; public Sigstore services, OCI registries, cloud KMS providers, Vault providers, CI platforms, artifact stores, policy engines, and downstream deployment systems may have separate licenses, billing, terms, privacy obligations, and access controls.