From mboxrd@z Thu Jan 1 00:00:00 1970 From: ross@lug.udel.edu Subject: Re: SHA1 hash safety Date: Sat, 16 Apr 2005 11:49:51 -0400 Message-ID: <20050416154951.GB13373@jose.lug.udel.edu> References: <20050416123155.GA19908@elte.hu> <4261132A.3090907@khandalf.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: omb@bluewin.ch, David Lang , Ingo Molnar , git@vger.kernel.org X-From: git-owner@vger.kernel.org Sat Apr 16 17:46:34 2005 Return-path: Received: from vger.kernel.org ([12.107.209.244]) by ciao.gmane.org with esmtp (Exim 4.43) id 1DMpUv-0006GW-SN for gcvg-git@gmane.org; Sat, 16 Apr 2005 17:46:18 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262689AbVDPPtz (ORCPT ); Sat, 16 Apr 2005 11:49:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262690AbVDPPtz (ORCPT ); Sat, 16 Apr 2005 11:49:55 -0400 Received: from jose.lug.udel.edu ([128.175.60.112]:62868 "HELO mail.lug.udel.edu") by vger.kernel.org with SMTP id S262689AbVDPPtv (ORCPT ); Sat, 16 Apr 2005 11:49:51 -0400 Received: (qmail 13755 invoked by uid 1009); 16 Apr 2005 15:49:51 -0000 To: "C. Scott Ananian" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.6+20040907i Sender: git-owner@vger.kernel.org Precedence: bulk X-Mailing-List: git@vger.kernel.org On Sat, Apr 16, 2005 at 10:58:15AM -0400, C. Scott Ananian wrote: > Even given the known weaknesses in MD5, it would take much more than a > million documents to find MD5 collisions. I can only conclude that the > hash was being used incorrectly; most likely truncated (my wild-ass guess > would be to 32 bits; a collision is likely with > 50% probability in a > million document store for a hash of less than 40 bits). I've also seen non thread-safe GUID generation, using MD5m hit collisions: but of course that was due to the fact that the code had thread safety issues, not because anyone actually ever hit a MD5 collision... Of course there are constructed cases of MD5 collision, but those are pretty disinteresting. Give me two files that have useful content and the same hash, and then I'll be impressed. Linus has already weighed in that he doesn't give a crap. All the crypto-babble about collision whitepapers is uninteresting without a repo that has real collisions. git is far too cool as is - prove I should be concerned. -- Ross Vandegrift ross@lug.udel.edu "The good Christian should beware of mathematicians, and all those who make empty prophecies. The danger already exists that the mathematicians have made a covenant with the devil to darken the spirit and to confine man in the bonds of Hell." --St. Augustine, De Genesi ad Litteram, Book II, xviii, 37