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Conex is a utility for verify and attest release integrity and authenticity of community repositories through the use of cryptographic signatures (RSA-PSS-SHA256). It is based on the update framework, especially on their CCS 2010 paper, and adapted to the requirements of the opam repository.
The developer sign their release checksums and build instructions. A quorum (with a configurable threshold) of repository maintainers signs the package name to developer key relation. These repository maintainers are enrolled by a quorum of offline root keys.
The TUF spec has a good overview of attacks and threat model, both of which are shared by conex.
Spring 2017, together with Justin Cappos TAP 8 was designed which extends TUF with key rotation and explicit self-revocation.
Early 2017, a blog post introducing a prototype was published.
We presented an earlier design at OCaml 2016 about an earlier design.
Another article on an even earlier design (from 2015) is also available.
Conex release tarballs are accompanied with OpenPGP signatures in a separate .sig file in the download area.
opam instal conex will install this library and tool,
once you have installed OCaml (>= 4.13.0) and opam (>= 2.0.0beta).
A small test repository with two maintainers is available here including transcripts of how it was setup, and how to setup opams repo validation hook.