Cosign vs SignServer

Cosign is a free tool for signing and verifying OCI container images and other software artifacts. It can store container signatures in an OCI registry and publish generic artifacts through OCI. Supported targets include blobs, binaries, scripts, configuration files, SBOMs, WASM modules, Tekton bundles, eBPF modules, and in-toto attestations whose payloads use DSSE. Its default keyless workflow uses temporary keys held in memory, short-lived certificates from Sigstore’s Fulcio certificate authority, and entries in the Rekor transparency log. Other signing options include hardware and KMS-backed keys, encrypted keypairs generated by Cosign, and user-provided PKI. Cosign supports CI/CD signing, with guidance for GitHub Actions and GitLab CI/CD. Offline verification is possible when the image and signature materials are available locally and a trusted root is supplied. The project describes Cosign as a legacy signing system and recommends Sigstore-go for verification integrations. Its CLI-focused design has no API stability guarantees, and the documentation does not recommend it for application integration.

SignServer is a server-side platform that centrally manages signing keys and digitally signs code, documents, and timestamps. One installation can serve several signing workflows, including containers, firmware, IoT, and DevOps use cases. It can connect to CI/CD pipelines, firmware build processes, document workflow engines, identity platforms, and other applications through standard interfaces. Community is available as a Docker container, Helm chart, source code, or GitHub release, and is also listed on SourceForge. Its interfaces include SOAP, HTTP, REST, and the SignClient command-line interface, though Community REST lacks some endpoints. Community is released under LGPL V2.1 or later and is intended for learning, testing, and prototyping rather than production. The maker says it lacks production capabilities such as audit, compliance, SLA, high availability, and security features. Enterprise adds professional support with an SLA, security updates, and maintenance. The Community plan is free; the Enterprise Cloud trial is free for 30 days through AWS or Azure marketplaces. The maker recommends Hardware Security Modules for signing-key storage.