From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: Exploiting SHA1's "XOR weakness" allows for faster hash calculation Date: Wed, 5 Dec 2012 12:20:11 -0500 Message-ID: <20121205172011.GH18885@thunk.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: git@vger.kernel.org To: Sebastian Schuberth X-From: git-owner@vger.kernel.org Wed Dec 05 18:20:37 2012 Return-path: Envelope-to: gcvg-git-2@plane.gmane.org Received: from vger.kernel.org ([209.132.180.67]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1TgIeB-0001gy-QM for gcvg-git-2@plane.gmane.org; Wed, 05 Dec 2012 18:20:36 +0100 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754057Ab2LERUR (ORCPT ); Wed, 5 Dec 2012 12:20:17 -0500 Received: from li9-11.members.linode.com ([67.18.176.11]:36967 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753735Ab2LERUQ (ORCPT ); Wed, 5 Dec 2012 12:20:16 -0500 Received: from root (helo=closure.thunk.org) by imap.thunk.org with local-esmtp (Exim 4.72) (envelope-from ) id 1TgIdf-00028V-EN; Wed, 05 Dec 2012 17:20:03 +0000 Received: by closure.thunk.org (Postfix, from userid 15806) id CDFC7241B85; Wed, 5 Dec 2012 12:20:11 -0500 (EST) Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: On Wed, Dec 05, 2012 at 10:19:43AM +0100, Sebastian Schuberth wrote: > > to say it in advance: I do not want to trigger any bogus security > discussion here. Instead, I believe the findings from [1] allow for > an up to 20% faster SHA1 calculation, if my brief reading of the > presentation is correct. Any opinions on integration this > optimization into Git? > > [1] https://hashcat.net/p12/js-sha1exp_169.pdf It's only useful if you are trying to do brute-force password cracking, where the password is being hashed in a very specific way. (If for example the password was replicated N times in the input buffer for SHA-1, instead of keeping the padding constant in the rest of theinput buffer, this particular optimization would't apply.) In any case, it's not at all applicable for general purpose checksum calculations, and hence wouldn't apply to git. Regards, - Ted