Re: [PATCH RFC v1 1/3] bpf: move from sha1 to blake2s in tag calculation

["Jason A. Donenfeld" <Jason@zx2c4.com>]

On Fri, Jan 14, 2022 at 4:08 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> Yeah, so the issue is that, at *some* point, SHA-1 is going to have to
> go. So it would be helpful if Alexei could clarify *why* he doesn't
> see this as a problem. The fact that it is broken means that it is no
> longer intractable to forge collisions, which likley means that SHA-1
> no longer fulfills the task that you wanted it to do in the first
> place.

I think the reason that Alexei doesn't think that the SHA-1 choice
really matters is because the result is being truncated to 64-bits, so
collisions are easy anyway, regardless of which hash function is
chosen (birthday bound and all). But from Geert's perspective, that
SHA-1 is still taking up precious bytes in m68k builds. And from my
perspective, it's poor form and clutters vmlinux, and plus, now I'm
curious about why this isn't using a more appropriately sized tag in
the first place.

On Fri, Jan 14, 2022 at 3:12 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> "checksum" -- the thing is only 64-bits, and as you told Andy Polyakov

Whoops, meant Lutomirski here. x86 Andy, not crypto Andy :)