From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.6 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 0B3512022D for ; Thu, 23 Feb 2017 17:20:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751585AbdBWRUJ (ORCPT ); Thu, 23 Feb 2017 12:20:09 -0500 Received: from lang.hm ([66.167.227.134]:60157 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751198AbdBWRUF (ORCPT ); Thu, 23 Feb 2017 12:20:05 -0500 X-Greylist: delayed 680 seconds by postgrey-1.27 at vger.kernel.org; Thu, 23 Feb 2017 12:20:01 EST Received: from dlang-laptop ([10.2.0.162]) by bifrost.lang.hm (8.13.4/8.13.4/Debian-3) with ESMTP id v1NH0Kbi008180; Thu, 23 Feb 2017 09:00:20 -0800 Date: Thu, 23 Feb 2017 09:00:20 -0800 (PST) From: David Lang X-X-Sender: dlang@dlang-laptop To: Joey Hess cc: git@vger.kernel.org Subject: Re: SHA1 collisions found In-Reply-To: <20170223164306.spg2avxzukkggrpb@kitenet.net> Message-ID: References: <20170223164306.spg2avxzukkggrpb@kitenet.net> User-Agent: Alpine 2.20.17 (DEB 179 2016-10-28) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Thu, 23 Feb 2017, Joey Hess wrote: > https://shattered.io/static/shattered.pdf > https://freedom-to-tinker.com/2017/02/23/rip-sha-1/ > > IIRC someone has been working on parameterizing git's SHA1 assumptions > so a repository could eventually use a more secure hash. How far has > that gotten? There are still many "40" constants in git.git HEAD. > > In the meantime, git commit -S, and checks that commits are signed, > seems like the only way to mitigate against attacks such as > the ones described in the threads at > https://joeyh.name/blog/sha-1/ and > https://joeyh.name/blog/entry/size_of_the_git_sha1_collision_attack_surface/ > > Since we now have collisions in valid PDF files, collisions in valid git > commit and tree objects are probably able to be constructed. keep in mind that there is a huge difference between creating a collision between two documents you create, both of which contain a huge amount of arbitrary binary data that can be changed at will without affecting the results and creating a collision betwen an existing document that someone else created and a new document that is also valid C code without huge amounts of binary in it. So, it's not time to panic, but it is one more push to make the changes to support something else. David Lang