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

[Sam James]

> On 6 Apr 2022, at 01:15, Jason A. Donenfeld <zx2c4@g.o> wrote:
>
> Hi Sam,
>
> On Wed, Apr 6, 2022 at 2:02 AM Sam James <sam@g.o> wrote:
>> This matches my views and recollection. We could revisit it
>> if there was a passionate advocate (which it looks like there may well be).
>>
>> While I wasn't against it before, I was sort of ambivalent given
>> we had no strong reason to, but I'm more willing now given
>> we're also cleaning out other Portage cruft at the same time.
>
> I think actually the argument I'm making this time might be subtly
> different from the motions that folks went through last year.
> Specifically, the idea last year was to switch to using BLAKE2b only.
> I think what the arguments I'm making now point to is switching to
> SHA2-512 only.

Oh, right. I see!

(Aside: I should've been clearer in my first email, what I meant was: I'm
fine with revisiting this, but I remember us feeling kind of lacklustre because
even the proposer (mgorny) ended up not having the oomph to push it through
given (small) opposition. I don't recall who had the stiff opposition at the time,
but I do recall it was only small, but nobody really felt like it was worth the hassle.

The overall Council feeling was "meh" without some momentum.)


> There are two reasons for this.
>
> 1) Security: since the GPG signatures use SHA2-512, then the whole
> system breaks if SHA2-512 breaks. If we choose BLAKE2b as our only
> hash, then if either SHA2-512 or BLAKE2b break, then the system
> breaks. But if we choose SHA2-512 as our only hash, then we only need
> to worry about SHA2-512 breaking.
>
> 2) Comparability: other distros use SHA2-512, as well as various
> upstreams, which means we can compare our hashes to theirs easily.
>
> A reason why some people might prefer BLAKE2b over SHA2-512 is a
> performance improvement. However, seeing as right now we're opening
> the file, reading it, computing BLAKE2b, closing the file, opening the
> file again, reading it again, computing SHA2-512, closing the file, I
> don't think performance is actually something people care about. Seen
> differently, removing either one of them will already give us a
> performance "boost" or sorts.
>

I think this seems pretty reasonable and I don't have any objection to it.

2) is a nice point and it's something Robin raised last time around too.

> Jason

best,
sam