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,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RCVD_IN_SORBS_SPAM, RP_MATCHES_RCVD shortcircuit=no autolearn=no 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 AA5FD2022D for ; Thu, 23 Feb 2017 20:49:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751308AbdBWUtS (ORCPT ); Thu, 23 Feb 2017 15:49:18 -0500 Received: from mail-lf0-f50.google.com ([209.85.215.50]:33600 "EHLO mail-lf0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751224AbdBWUtS (ORCPT ); Thu, 23 Feb 2017 15:49:18 -0500 Received: by mail-lf0-f50.google.com with SMTP id l12so1227236lfe.0 for ; Thu, 23 Feb 2017 12:49:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:cc:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding; bh=sV6iZJD4hd8KFxEGtqyTQe9VEHukfn1cvlgKUl7BfNc=; b=sTuP+3OQSJ61g106kyUE9rKx/V5hixGVO45pAwT9ECmQkB1St3IW2B39eOt8KLzXgX F4gG5zIZxFUchiMqJ81I0KhMolXX7cd+6Oz4ufp6hhA1MdOlrlTxJN4rl60cmUghW5AM N+gNOosGJCdEodwCXGGvIEVsGNexFU7ixvEOwKx2ENQMqdfVjB3TNSoFboEYsY+XaiWf I1Snj8hz34AJx3ri8JpgTkX3GzKZ9Yjcdtht7hFAgrDLg1N0GSe8EwO97SHJyxk/i7it lzMeSmS0PZtB/mI6TzovSkZSuzciUXdHIDEfrHUEaSlWwU8gp0ZJDYjFvDKdwAMME1OA yGJg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:cc:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=sV6iZJD4hd8KFxEGtqyTQe9VEHukfn1cvlgKUl7BfNc=; b=Kmdpy89ZL29LJBOL9L4tMzooZQEQXhlrPeeQuDhE3BZ1wNLdJ02uozzW8e/FR8wDHT FSvMkRXbz7WGVncO42/Oo5TRwaUBqufQKA5kp4K3hQq+PT5EI7JMz06xUOYOvKKgh6aC rGpewqMHxd8SXNGLGra17AncEG3PnaFOtr30morS+Iib+TI9TqyKU1Zd5FuzmX05Z5M5 fPfk13uTNfJyj+1P4zi2vJghlEH5cshZpE5lNKUlRd30+fCHW6i2Z07YI2rhb/5CWl1v c1zIQQsct4UdHg6oxaf17ZWJIRjkcYDJ4VKl4q0tyxMbqBig/2P+vD4hF0+2SPeltSIS OnSQ== X-Gm-Message-State: AMke39mnt/oZXHApj81cXdtKYeUQHOT3jtaGFZwucUvmUaXiIDwzX+R2WGwYc/5FwpnEWg== X-Received: by 10.25.79.69 with SMTP id a5mr1864362lfk.58.1487882956074; Thu, 23 Feb 2017 12:49:16 -0800 (PST) Received: from [192.168.1.26] (elt110.neoplus.adsl.tpnet.pl. [83.21.213.110]) by smtp.googlemail.com with ESMTPSA id 5sm8375885lja.58.2017.02.23.12.49.14 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Feb 2017 12:49:15 -0800 (PST) Subject: Re: SHA1 collisions found To: David Lang , Junio C Hamano References: <20170223164306.spg2avxzukkggrpb@kitenet.net> Cc: Joey Hess , Git Mailing List From: =?UTF-8?Q?Jakub_Nar=c4=99bski?= Message-ID: Date: Thu, 23 Feb 2017 21:49:09 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org W dniu 23.02.2017 o 18:12, David Lang pisze: > 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. The attack on SHA-1 presented there is "identical-prefix" collision, which is less powerful than "chosen-prefix" collision. It is the latter that is required to defeat SHA-1 used in object identity. Objects in Git _must_ begin with given prefix; the use of zlib compression adds to the difficulty. 'Forged' Git object would simply not validate... https://arstechnica.com/security/2017/02/at-deaths-door-for-years-widely-used-sha1-function-is-now-dead/