Cybersecurity · head to head
Cosign vs Proton Mail
Cosign
Cybersecurity
Signs and verifies container images and artifacts, with or without managing keys
- 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.; Proton Mail paid plan pricing not displayed on vendor site
- Prices and features above were last checked on 31 August 2026.
Where they differ
Only the attributes on which Cosign and Proton Mail actually diverge.
| Attribute | Cosign | Proton Mail |
|---|---|---|
| Pricing model | Open source, no licence fee | freemium |
| Platforms | macOS, Linux, Windows, Docker | Web |
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
- Keyless signing
- Key and KMS signing
- Registry-native storage
- In-toto attestations
- Offline verification
- Trusted root and signing config
Only in Proton Mail
Nothing recorded that Cosign does not also cover.
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 Proton Mail
- Attaching a signed bill of materials to a release so consumers can verify its provenancenot Proton Mail
- Meeting a customer or regulatory requirement for signed artifactsnot Proton Mail
- Verifying third-party images before they enter an internal registrynot Proton Mail
Proton Mail
- Encrypted email communicationnot Cosign
- Privacy-focused email servicenot Cosign
- Family email protectionnot 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.
Proton Mail
- Paid plan pricing not displayed on vendor site
- Free tier limited to 1 GB storage
- Free tier limited to single email address
Pricing, plan by plan
Cosign
Free- CosignFree
- Apache-2.0
- Public Sigstore infrastructure free to use
- No usage limits published
Proton Mail
FreeNo published plan breakdown. See the Proton Mail review.
Which should you pick?
Choose Cosign if
- You need keyless signing.
- You want to start without paying.
- You work on macOS, Linux, Windows, Docker.
- You also want key and kms signing.
Questions people ask
- Is Cosign or Proton Mail better?
- Neither clearly leads. Cosign starts at Free and Proton Mail at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
- Which is cheaper, Cosign or Proton Mail?
- Cosign starts at Free and Proton Mail at Free.
- Does Cosign or Proton Mail run on more platforms?
- Cosign runs on macOS, Linux, Windows, Docker. Proton Mail runs on Web.
- 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 Proton Mail is typically brought in for.
- What can Cosign do that Proton Mail cannot?
- Cosign covers Keyless signing, Key and KMS signing, Registry-native storage, In-toto attestations.
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.
Proton Mail: Is there a free version of Proton Mail?
Yes, Proton Mail offers a free plan with 1 GB storage, 1 encrypted email address, and basic features like folders, labels, and filters.
SourceCosign: Is signing alone enough?
No. Verification is a command somebody runs. Without an admission controller enforcing it, an unsigned image still runs.
Proton Mail: What does the Mail Plus plan include?
Mail Plus includes 15 GB storage, 10 encrypted email addresses, support for 1 custom domain, 10 hide-my-email aliases, priority support, and access to Proton Calendar.
SourceCosign: 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.
Proton Mail: What is included in Proton Unlimited?
Proton Unlimited provides 500 GB storage, 15 email addresses, 3 custom domains, unlimited hide-my-email aliases, access to Mail, Calendar, VPN, Drive, and Pass, plus dedicated support.
SourceCosign: 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.
Proton Mail: Does Proton Mail offer a money-back guarantee?
Yes, Proton Mail provides a 30-day money-back guarantee for paid plans.
SourceCosign: 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.
Related pages
More on Proton Mail
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