Re: Git and SHA-1 security (again)

From: Theodore Ts'o <tytso@mit.edu>
Date: Jul 17, 2016, 16:23 UTC
Message-ID: <20160717162349.GB11276@thunk.org>
In-Reply-To: <20160717154234.GC6644@vauxhall.crustytoothpaste.net>

On Sun, Jul 17, 2016 at 03:42:34PM +0000, brian m. carlson wrote:

> As I said, I'm not planning on multiple hash support at first, but it
> doesn't appear impossible if we go this route.  We might still have to
> rewrite objects, but we can verify signatures over the legacy SHA-1
> objects by forcing them into the old-style object format.

How hard would it be to make the on-disk format be multihash, even if there is no support for anything other than a single hash, at least for now? That way we won't have to rewrite the objects twice.

Personally, so long as the newer versions of the tree are secured, I wouldn't mind if the older commits stayed using SHA1 only. The newer commits are the ones that are most important and security-critical anyway. It seems like the main reason to rewrite all of the objects is to simplify the initial rollout of a newer hash algorithm, no?

		     	   		   - Ted