attestation VS dsse

It's multi-pronged and I imagine adopters may use a subset of features. Broadly, I think folks are going to be interested in a) branch/tag/reference protection rules, b) file protection rules (monorepo or otherwise, though monorepos do pose a very apt usecase for gittuf), and c) general key management for those who primarily care about Git signing.

For those who care about a and b, I think the work we want to do to support [in-toto attestations](https://github.com/in-toto/attestation) for [SLSA's upcoming source track](https://github.com/slsa-framework/slsa/issues/956) could be very interesting as well.

I have. I actually worked a few desks down from dpc when he was creating it and we talked about it at length. I felt then and now that it has good goals but a very limiting implementation in that it does not pursue a portable spec and instead anchors a very opinionated format to git, and github, instead of cryptographic keys held in hardware owned controlled by reviewers. I want to see the same keys that sign git commits also sign reviews, for instance.

I think for broad adoption a review system should ask essentially the same questions as crev, but store them in a format like in-toto including signatures by the reviewers created with a user choice of pgp smartcards, ssh keys, or webauthn devices. These reviews would be anchored to hashes of a particular state of a particular tree of code and not to any type of VCS or distribution system. Important code is distributed via Perforce, mercurial subversion, and tar files depending if we are talking about big corps, or linux distro building blocks. A good OSS review system should be also be usable by teams in their internal proprietary codebases too if we wish to see wide adoption. Even for OSS we may wish to share some reviews as standalone objects privately while security embargos are in place, etc. Proofs should also be verified standalone easily from local cache, when github is down, when original repos vanish, etc.

Something that meets these broader needs will make it easy for large orgs with very different internal setups to participate and play nice with other supply chain efforts by the OpenSSF using in-toto for reproducible builds, etc.

My experience tells me we need something much more ambitious than crev, but crev proved to me many people have real interest in this problem which I really thank dpc for.

The biggest blocker for starting this project is the human review spec settling in in-toto https://github.com/in-toto/attestation/issues/77

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.