Re: About git and the use of SHA-1

From: Geoffrey Irving <irving@naml.us>
Date: Apr 29, 2008, 18:02 UTC
Message-ID: <7f9d599f0804291102j4a30c344h18d12d03a6d5953b@mail.gmail.com>
In-Reply-To: <alpine.LFD.1.10.0804291352120.23581@xanadu.home>

On Tue, Apr 29, 2008 at 10:55 AM, Nicolas Pitre <nico@cam.org> wrote:

Show 10 quoted lines

> On Tue, 29 Apr 2008, Geoffrey Irving wrote:
>
>
> > Sorry for the confusion: it would handwaving if I was saying git was insecure,
>  > but I'm not.  I'm saying that if or when SHA1 becomes vulnerable to collision
>  > attacks, git will be insecure.
>
>  Right.  And if or when that happens then we'll make Git secure again
>  with a different hash.  In the mean time there is low return for the
>  effort involved.

Yes. I wasn't trying to advocate switching, just making sure people know that the "collisions don't matter" argument is bogus.

One important thing: when SHA1 becomes vulnerable to collision attacks, it will still be secure to trust the repositories and tags that exist *at that moment.* I.e., the transition period from SHA1 to the next hash will also be secure, assuming that preimage attacks don't become possible simultaneously. So everything is good.

Geoffrey