fulcio VS dsse

untrue.

The Root CA is generated by the sigstore community (five folks, two from academia) this is what is used for the trust root for the signing. Right now github exchanges a OIDC token for a sigstore root chained cert.

GitLab are currently adding themselves, to have the same capability.

https://github.com/sigstore/fulcio/pull/1097

They also say thay they integrate with Fulcio which seems to be a self-managing CA. Never tried it, though.

https://docs.sigstore.dev/ :

> sigstore empowers software developers to securely sign software artifacts such as release files, container images, binaries, bill of material manifests and more. Signing materials are then stored in a tamper-resistant public log.

> It’s free to use for all developers and software providers, with sigstore’s code and operational tooling being 100% open source, and everything maintained and developed by the sigstore community.

> How sigstore works: Using Fulcio, sigstore requests a certificate from our root Certificate Authority (CA). This checks you are who you say you are using OpenID Connect, which looks at your email address to prove you’re the author. Fulcio grants a time-stamped certificate, a way to say you’re signed in and that it’s you.

https://github.com/sigstore/fulcio

> You don’t have to do anything with keys yourself, and sigstore never obtains your private key. The public key that Cosign creates gets bound to your certificate, and the signing details get stored in sigstore’s trust root, the deeper layer of keys and trustees and what we use to check authenticity.

https://github.com/sigstore/cosign

> our certificate then comes back to sigstore, where sigstore exchanges keys, asserts your identity and signs everything off. The signature contains the hash itself, public key, signature content and the time stamp. This all gets uploaded to a Rekor transparency log, so anyone can check that what you’ve put out there went through all the checks needed to be authentic.

https://github.com/sigstore/rekor

fulcio is a root CA for code signing certs. Its job is to issue code-signing certificates and to embed OIDC identity into code-signing certificate. From this description we can see that it performs these tasks in steps 2, 3, 4 and 8.

Did you follow the link to the project list on Github? The actual tool for doing the signing, cosign, is just a binary you can install on your device and generate signatures and keys yourself. The "service" part of it seems to just be having your public certificate vouched for by a trusted code signing CA. I don't see anything in the tooling that requires your users to only trust that CA. If you want to sign your cert with your own CA and tell your users to trust that instead, they seemingly can do that, just as you can do that today in browsers. That you can't do it with Firefox extensions and mobile app stores is a limitation intentionally built into the distribution channel. It's not a limitation of PKI itself. iOS, Android, and Mozilla could have chosen to let users install arbitrary trusted CAs. You shouldn't dismiss all PKI based on the fact that a few vendors have chosen to implement it in a crappy way to make walled gardens.

It doesn't say this on the announcement, but looking at the actual PKI service (https://github.com/sigstore/fulcio), it seems to be entirely possible to self-host the service and roll your own CA.

I took a look at the design and think there are a few issues with the format as proposed.

# The public key is stored with the signature.

This should be stored separately. A public key found here is too tempting to use, rendering the signature worthless. Authenticating it would be OK, but low value. This is unauthenticated. A "key ID" should be used instead if the intention is to support lookups among multiple keys.

# The algorithm is stored with the signature.

This is slightly less bad than above, but still bad. Attacker-controlled algorithms have been used repeatedly in "downgrade" attacks. Agility is bad, but if you must support multiple algorithms, store this with the public key (somewhere else). Some info here: https://github.com/secure-systems-lab/dsse/issues/35

I didn't look at the sub-key protocol in detail. The ephemeral key for every release is an interesting choice. The root key is "offline". But if it must be brought online to sign a new ephemeral key for every release anyway, you might as well just use it to sign the release itself.

Using minisign/signify like OpenBSD does and keeping things very simple makes sense to me. The complexity designed into this system (sub-keys, multiple algorithms and signatures) starts to stretch the bounds to where TUF (https://theupdateframework.io/) might make sense. TUF is very complex and not worth it for most projects, but Debian is exactly what TUF is designed for.