This is an experimental implementation of binary transparency for pacman, the Arch Linux package manager. This project was originally heavily inspired by prior work by Mozilla and then re-implemented with the rekor transparency log of sigstore.

Cryptographic signatures prove that a message originates from somebody with control over the private key, but it's impossible to prove that the private key didn't sign additional messages. In update security this means a signed update is a strong indicator the update is authentic, but you can't be sure this update is the same update everybody else got. Somebody in control of the update key could craft a malicious update, sign it and feed it specifically to you. This attack is much less likely to get noticed than pushing a malicious update to all users.

Because transparency logs work best with a "single-purpose key", meaning the key is only ever used to sign Arch Linux packages, we're creating a special "transparency key". The operator needs to sign every Arch Linux package and upload the signature to the transparency log. They also need to maintain an audit log that tracks why each signature was created.

An external auditor could then fetch all signatures from sigstore and check if they belong to officially released packages.

pacman-bintrans integrates into pacman by registering it as a custom transport in /etc/pacman.conf:

XferCommand = /usr/bin/pacman-bintrans -O %o %u --transparency-url https://pacman-bintrans.vulns.xyz/sigs/ --pubkey 'RWSC6c8TVaOYGoe60E+sPiPgumSQENiSNJrBOH6IUYdfmY9xIDJCFXa2'

To verify everything is working correctly you can clear your download cache with pacman -Scc and then try to re-download and reinstall a package with pacman -Suy filesystem.

pacman still verifies pgp signatures, but in addition also runs rekor-cli verify on each package to ensure it has been properly logged in the sigstore transparency log.

It's also possible to query rebuilders for the reproducible builds status of every downloaded package. To query a rebuilder add --rebuilder <url>, this option can be set multiple times:

XferCommand = /usr/bin/pacman-bintrans -O %o %u --transparency-url https://pacman-bintrans.vulns.xyz/sigs/ --pubkey 'RWSC6c8TVaOYGoe60E+sPiPgumSQENiSNJrBOH6IUYdfmY9xIDJCFXa2' --rebuilder https://reproducible.archlinux.org/ --rebuilder https://r-b.engineering.nyu.edu/ --rebuilder https://wolfpit.net/rebuild/

You can configure a threshold with --required-rebuild-confirms 1 so every package that hasn't been confirmed by this many rebuilders is rejected as untrusted. If you're relying on this option for security you're trusting the rebuilders you've configured with --rebuilder <url> to operate honestly.

TODO

This section is intended for package maintainers that are planning to run package repositories with binary transparency enabled.

cd pacman-bintrans-sign
cargo run --release -- -v \
    --repo-url 'https://ftp.halifax.rwth-aachen.de/archlinux/$repo/os/$arch' --repo-name core --architecture x86_64 \
    --signature-dir ../www/ --pubkey-path ~/keys/minisign.pub --seckey-path ~/keys/seckey

There's a command to list all signatures that have been logged so far:

cd pacman-bintrans-monitor
cargo run

Note this doesn't fully torify all traffic, it only uses it to download the package and fetch from --transparency-url:

cargo run -- -vvO filesystem-2021.05.31-1-x86_64.pkg.tar.zst https://ftp.halifax.rwth-aachen.de/archlinux/core/os/x86_64/filesystem-2021.05.31-1-x86_64.pkg.tar.zst \
    --pubkey 'RWSC6c8TVaOYGoe60E+sPiPgumSQENiSNJrBOH6IUYdfmY9xIDJCFXa2' --transparency-url 'http://2iz5fzvuwjapcv5v2msvhlr5oqbwriznwu7hnsccrsho47ljqynrgryd.onion/sigs/' \
    --proxy 'socks5h://127.0.0.1:9050' --bypass-proxy-for-pkgs

This project was funded by Google, The Linux Foundation, and people like you and me through GitHub sponsors. ♥️♥️♥️

GPLv3+