[gentoo-dev] proposal: use only one hash function in manifest files

[Jason A. Donenfeld]

Hi,

I'd like to propose the following for portage:

- Only support one "secure" hash function (such as sha2, sha3, blake2, etc)
- Only generate and parse one hash function in Manifest files
- Remove support for multiple hash functions

In other words, what are we actually getting by having _both_ SHA2-512
and BLAKE2b for every file in every Manifest? It's not about file
integrity, since certainly a single hash handles that use case fine.
And it's not about security either, since for that we use gpg
signatures, and gpg signatures are carried out over a _single_ hash of
the plain text being hashed, so the security of the system reduces to
breaking SHA2-512 anyway. So, if it's not about file integrity and
it's not about security, what is it about?

I don't really care which one we use, so long as it's not already
broken or too obscure/new. So in other words, any one of SHA2-256,
SHA2-512, SHA3, BLAKE2b, BLAKE2s would be fine with me. Can we just
pick one and roll with it?

Jason

PS: there _is_ a good reason for recording the file size in Manifest
files as we do now: it's quicker to compare sizes on large files than
it is to read and hash the whole thing, so this gives us a "free" way
of noticing quick corruption.