From: Junio C Hamano <gitster@pobox.com>
Date: Mon, 27 Mar 2017 17:15:07 GMT
Subject: Re: [PATCH 0/7] PREVIEW: Introduce DC_AND_OPENSSL_SHA1 make flag
Message-ID: <xmqqy3vq1w10.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170327070909.26ojhkhagf6pq3wp@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

> Yeah, I think we can assume it will be possible with SHAttered levels of
> effort. An attacker can use it to create a persistent corruption by
> having somebody fetch from them twice. So not really that interesting an
> attack, but it is something. I still think that ditching SHA-1 for the
> naming is probably a better fix than worrying about SHA-1 collisions.

Yes, I agree with that part.  

Our trailer checksum happens to be SHA-1 mostly because the code was
available, not because they need to be a crypto-strong hash.  It can
safely be changed to something other than SHA-1 that is much faster,
if that is desired, when it is used only for bit-flip detection of
local files like the index file.

I also agree that changing the naming scheme (e.g. use the "hash" as
a hash to choose hash-bucket but accept the fact that hashes can
collide) is a better solution, if this "packname can collide" were
to become real problem.

Thanks.