Cybersecurity · head to head
Cosign vs Sigstore
Cosign
Cybersecurity
Signs and verifies container images and artifacts, with or without managing keys
- From
- Free
- Rated
- -
Sigstore
Cybersecurity
Free public signing and transparency infrastructure for open source artifacts
- From
- Free
- Rated
- -
The short version
- Each has a real cost: Cosign keyless signing inherits every weakness of the identity provider behind it. Sigstore’s own threat model states that if an identity provider is compromised, Sigstore will issue certificates to those identities, so a compromised account produces perfectly valid signatures.; Sigstore the security model depends on somebody watching the log. The documentation states that compromise of an identity provider or of Fulcio itself is detectable only if third parties monitor the transparency log, the monitoring tool is a community-tier rather than core project, and almost no consumer runs one.
- They diverge on capability: Cosign covers Key and KMS signing, Sigstore covers Fulcio.
- Prices and features above were last checked on 31 August 2026.
Where they differ
Only the attributes on which Cosign and Sigstore actually diverge.
Identical on both: starting price (Free), free tier (Yes), user rating (Not yet rated), category (Cybersecurity).
What each one covers
Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.
Only in Cosign
- Key and KMS signing
- Registry-native storage
- In-toto attestations
- Offline verification
- Trusted root and signing config
Only in Sigstore
- Fulcio
- Rekor
- Multi-language clients
- Timestamp authority
- Neutral governance
Both cover
- Keyless signing
What people use each for
The jobs each tool is most often brought in to do.
Cosign
- Signing container images in a build pipeline without managing long-lived private keysnot Sigstore
- Attaching a signed bill of materials to a release so consumers can verify its provenancenot Sigstore
- Meeting a customer or regulatory requirement for signed artifactsnot Sigstore
- Verifying third-party images before they enter an internal registrynot Sigstore
Sigstore
- Open source projects signing releases without running a certificate authoritynot Cosign
- Organisations meeting a signed-artifact requirement without buying a signing productnot Cosign
- Publishing provenance that a consumer can verify independently of younot Cosign
- Self-hosting the same components where a public log is unacceptablenot Cosign
Where each one falls short
Documented limitations, not opinions. Every one is a constraint you would hit in normal use.
Cosign
- Keyless signing inherits every weakness of the identity provider behind it. Sigstore’s own threat model states that if an identity provider is compromised, Sigstore will issue certificates to those identities, so a compromised account produces perfectly valid signatures.
- A signature proves who signed, never whether they should have. The documentation is explicit that Sigstore cannot determine authorisation, so every consumer must write and maintain their own identity and issuer policy or verification means nothing.
- Nothing is enforced without an admission controller. Signing changes what you can prove, not what runs, and the official policy controller has a small maintainer base for a component sitting in a cluster admission path.
- Upgrades break pipelines. Version 3 changed defaults, version 4 is announced as removing legacy functionality and roughly half the command line flags, and two official client libraries still lacked support for the new log format as of mid 2026.
- Signatures do not expire. An artifact signed before a maintainer account was compromised and one signed after are indistinguishable unless somebody is actively monitoring the transparency log, and almost nobody is.
Sigstore
- The security model depends on somebody watching the log. The documentation states that compromise of an identity provider or of Fulcio itself is detectable only if third parties monitor the transparency log, the monitoring tool is a community-tier rather than core project, and almost no consumer runs one.
- It is a 99.5 percent objective with no service level agreement, which permits several hours of downtime a month and offers no remedy. A pipeline that signs on every build has taken a hard dependency on a free service with no contract behind it.
- Log scale is a live engineering problem rather than a theoretical one. The active shard holds billions of entries, the log has already been sharded twice, and sharding version 1 requires stopping traffic, which is why a replacement was built.
- Ten-minute certificates make trust depend on log availability. Verifying an older signature relies on the log entry proving it was made inside that window, so a lost or unreachable entry can render a valid artifact unverifiable.
- Migration debt is substantial and ongoing. Version 2 of the log is generally available but not the public default, the signing client has an announced breaking release ahead, some official clients lag the new log format, and a post-quantum migration is named as the next break after that.
Pricing, plan by plan
Cosign
Free- CosignFree
- Apache-2.0
- Public Sigstore infrastructure free to use
- No usage limits published
Sigstore
Free- Public good instanceFree
- Free to everyone with no contract
- 99.5 percent availability objective, not an agreement
- 100KB cap per attestation upload
- Self-hostedFree
- Apache-2.0
- Run your own Fulcio and Rekor
- Rekor v2 available for self-hosters
Which should you pick?
Choose Cosign if
- You need key and kms signing.
- You want to start without paying.
- You work on macOS, Linux, Windows, Docker.
- You also want registry-native storage.
Choose Sigstore if
- You need fulcio.
- You want to start without paying.
- You work on Web, Linux, macOS, Windows, Self-hosted.
- You also want rekor.
Questions people ask
- Is Cosign or Sigstore better?
- Neither clearly leads. Cosign starts at Free and Sigstore at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
- Which is cheaper, Cosign or Sigstore?
- Cosign starts at Free and Sigstore at Free.
- Does Cosign or Sigstore run on more platforms?
- Cosign runs on macOS, Linux, Windows, Docker. Sigstore runs on Web, Linux, macOS, Windows, Self-hosted.
- Can I use Cosign for free?
- Both have a free tier, so you can try either at no cost before committing.
- What is Cosign best used for?
- Cosign is most often used for signing container images in a build pipeline without managing long-lived private keys, attaching a signed bill of materials to a release so consumers can verify its provenance, meeting a customer or regulatory requirement for signed artifacts, verifying third-party images before they enter an internal registry. Of those, signing container images in a build pipeline without managing long-lived private keys and attaching a signed bill of materials to a release so consumers can verify its provenance are not what Sigstore is typically brought in for.
- What can Cosign do that Sigstore cannot?
- Cosign covers Key and KMS signing, Registry-native storage, In-toto attestations, Offline verification. Sigstore covers Fulcio, Rekor, Multi-language clients, Timestamp authority. Both handle Keyless signing.
Answered from the vendors’ own pages
Cosign: Does Cosign tell me if an image is vulnerable?
No. It has no vulnerability knowledge whatsoever. It can carry an SBOM as a signed attestation but never reads it. Pair it with a scanner.
Sigstore: Is the public instance really free?
Yes, with no contract and no paid tier. That is also the weakness: a 99.5 percent objective with no agreement, no remedy and support through Slack.
Cosign: Is signing alone enough?
No. Verification is a command somebody runs. Without an admission controller enforcing it, an unsigned image still runs.
Sigstore: Has the public log moved to Rekor v2?
No. Version 2 reached general availability in October 2025 and self-hosters can use it, but the public instance still defaults to version 1 and the project has said it will for the foreseeable future.
Cosign: What does a bare cosign verify actually prove?
Very little. Without a pinned certificate identity and OIDC issuer, it accepts a valid signature from any identity at all.
Sigstore: Does Sigstore make my dependencies safe?
No, and this is a category error worth avoiding. It tells you who published something. It has no knowledge of what the artifact contains or whether it is vulnerable.
Cosign: What is the risk of keyless signing?
Your OIDC provider becomes the root of trust. Compromise of that account yields genuine, verifiable signatures, so account security is the control that matters.
Sigstore: What are the rate limits?
Not published. Only the 100KB cap per attestation upload is documented, so do not design a high-volume pipeline around assumed throughput.
Cosign: Should we expect breaking changes?
Yes. Version 4 is announced to remove roughly half the flags, and a post-quantum migration is named as a further breaking change after that.
Sigstore: Should we self-host it?
If a public record of every signature is unacceptable, or if a free service with no agreement cannot sit in your build path, then yes. Otherwise the public instance is what most projects use.
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