# Cosign

> Cosign is the command-line client of the Sigstore project for signing, verifying and storing
> container images, OCI artifacts, blobs and in-toto attestations. It supports keyless signing using
> OIDC identity providers by obtaining short-lived certificates from the Fulcio certificate authority
> and recording signing events in the Rekor transparency log. Signatures and attestations are stored
> alongside the signed artifact in any OCI-compliant registry. Apache-2.0, open source, no account,
> no pricing.

Generated 2026-09-07 by the API Evangelist enrichment pipeline from this repository's apis.yml and
artifacts. Not published by Sigstore — https://docs.sigstore.dev/llms.txt returned HTTP 404 on
2026-09-07, as did every /.well-known/ path on every Sigstore host.

## What Cosign is, and is not

- Cosign is a CLI. It publishes **no HTTP API and no OpenAPI of its own.**
- It calls three Sigstore public-good services: Fulcio (CA, https://fulcio.sigstore.dev), Rekor
  (transparency log, https://rekor.sigstore.dev) and a timestamp authority, plus a TUF-distributed
  trust root. Those are sibling projects in the same GitHub organization, not Cosign endpoints.
- The importable first-party library is the Go module `github.com/sigstore/cosign/v3`. There is no
  first-party JavaScript, Python, Ruby, Java or Rust client. The npm package named "cosign" is an
  unrelated Bitcoin tool.

## The one thing an agent must know before acting

Keyless signing writes a **permanent, public, unremovable** entry to the Rekor append-only
transparency log, including the signer's OIDC identity. `cosign clean` reverses the registry side
only. There is no delete, no redact and no expiry on the log side. Rehearse against the sigstage.dev
staging deployment first.

## Documentation

- [Cosign docs](https://docs.sigstore.dev/cosign/)
- [Quickstart](https://docs.sigstore.dev/quickstart/quickstart-cosign/)
- [Installation](https://docs.sigstore.dev/cosign/system_config/installation/)
- [Signing overview](https://docs.sigstore.dev/cosign/signing/overview/)
- [Verifying](https://docs.sigstore.dev/cosign/verifying/verify/)
- [Key management](https://docs.sigstore.dev/cosign/key_management/overview/)
- [Public deployment and staging](https://docs.sigstore.dev/cosign/system_config/public_deployment/)
- [CLI reference (generated, in-repo)](https://github.com/sigstore/cosign/tree/main/doc)
- [Specifications](https://github.com/sigstore/cosign/tree/main/specs)

## Source and releases

- [GitHub repository](https://github.com/sigstore/cosign)
- [GitHub organization](https://github.com/sigstore)
- [Releases](https://github.com/sigstore/cosign/releases) — v3.1.3 and v2.6.5, both 2026-08-06
- [CHANGELOG.md](https://github.com/sigstore/cosign/blob/main/CHANGELOG.md) — lags releases; stops at v3.0.5
- [Versioning and deprecation policy](https://github.com/sigstore/cosign/blob/main/VERSIONING.md)
- [CLI conventions](https://github.com/sigstore/cosign/blob/main/CLI.md)
- [Security policy](https://github.com/sigstore/.github/blob/main/SECURITY.md) — security@sigstore.dev, 24h acknowledgement
- [Status page](https://status.sigstore.dev/)

## Install

- `go install github.com/sigstore/cosign/v3/cmd/cosign@latest`
- `brew install cosign`
- `docker run --rm ghcr.io/sigstore/cosign/cosign:v3.1.3 version`
- GitHub Actions: `uses: sigstore/cosign-installer@main`

## Artifacts in this repository

- packages/cosign-packages.yml — every distribution channel with version and release date
- cli/cosign-cli.yml — the full command surface, grouped, with install methods and deprecations
- authentication/cosign-authentication.yml — the OIDC keyless model, KMS URIs, hardware tokens
- conventions/cosign-conventions.yml — output contract, idempotency (none) and reversibility
- errors/cosign-error-codes.yml — the documented exit codes 10-13
- lifecycle/cosign-lifecycle.yml — versioning, 6-month deprecation window, support policy, 99.5% SLO
- changelog/cosign-changelog.yml — two release lines, two channels, one of them stale
- conformance/cosign-conformance.yml — the supply-chain standards Cosign declares and CI-tests
- sandbox/cosign-sandbox.yml — the sigstage.dev staging deployment
- data-model/cosign-data-model.yml — signature, bundle, attestation, predicate, SBOM, log entry
- security/cosign-vulnerability-disclosure.yml — the Security Response Committee process
- security/cosign-domain-security.yml — TLS/HSTS/DNSSEC/CAA/SPF/DMARC probe
- well-known/cosign-well-known.yml — 35 probes across 5 hosts, all misses
- mcp/cosign-mcp.yml — candidate only; no MCP server exists
- skills/ — three packaged agent skills grounded in verified commands
- plans/cosign-plans-pricing.yml — zero plans; free open source
- rate-limits/cosign-rate-limits.yml — no published request limits, no rate-limit headers

## Optional

- [Sigstore blog](https://blog.sigstore.dev/)
- [Sigstore community](https://www.sigstore.dev/community)
- [Sigstore roadmap](https://github.com/sigstore/community/blob/main/ROADMAP.md)
- [OpenSSF Scorecard](https://scorecard.dev/viewer/?uri=github.com/sigstore/cosign) — 8.1 on 2026-09-06
- [Rekor transparency log](https://docs.sigstore.dev/logging/overview/)
- [Fulcio certificate authority](https://docs.sigstore.dev/certificate_authority/overview/)