And This is Why build2 Uses SHA256

I am sure most of you have heard the news by now. And that's why in build2 we use SHA256 from the outset. This is especially important for the bpkg(1) package manager since here we are talking about trust and not mere content addressing, as is the case with git.

The security model of bpkg revolves around a simple question: what happens when the server that hosts packages gets compromised? Note that it's "when", not "if".

So bpkg repositories are signed using the public/private key cryptography. More specifically, we generate an SHA256 sum for each package and then sign this list of packages and their hash sums (called the repository manifest) with the repository's private key. Provided you do this manifest generation and signing on a firewall'ed, secure machine, not much can happen if the package server gets compromised: the intruder cannot replace a package since that would require either altering the manifest (need private key) or forging the hash sum (need SHA1).

In fact, for we go a step further and keep the repository's private key on a Yubikey device, in case the secure machine gets stolen. For details see bpkg-repository-signing(1).