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 1CA592022D for ; Thu, 23 Feb 2017 17:28:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751882AbdBWR2j (ORCPT ); Thu, 23 Feb 2017 12:28:39 -0500 Received: from lang.hm ([66.167.227.134]:40877 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751735AbdBWR2i (ORCPT ); Thu, 23 Feb 2017 12:28:38 -0500 Received: from dlang-laptop ([10.2.0.162]) by bifrost.lang.hm (8.13.4/8.13.4/Debian-3) with ESMTP id v1NHCG9b008258; Thu, 23 Feb 2017 09:12:17 -0800 Date: Thu, 23 Feb 2017 09:12:16 -0800 (PST) From: David Lang X-X-Sender: dlang@dlang-laptop To: Junio C Hamano cc: Joey Hess , Git Mailing List Subject: Re: SHA1 collisions found In-Reply-To: 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, Junio C Hamano wrote: > On Thu, Feb 23, 2017 at 8:43 AM, Joey Hess wrote: >> >> Since we now have collisions in valid PDF files, collisions in valid git >> commit and tree objects are probably able to be constructed. > > That may be true, but > https://public-inbox.org/git/Pine.LNX.4.58.0504291221250.18901@ppc970.osdl.org/ > it doesn't help that the Google page on this explicitly says that this shows that it's possible to create two different git repos that have the same hash but different contents. https://shattered.it/ How is GIT affected? GIT strongly relies on SHA-1 for the identification and integrity checking of all file objects and commits. It is essentially possible to create two GIT repositories with the same head commit hash and different contents, say a benign source code and a backdoored one. An attacker could potentially selectively serve either repository to targeted users. This will require attackers to compute their own collision. David Lang