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=-3.5 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,T_DKIM_INVALID 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 9C2BB2022D for ; Thu, 23 Feb 2017 17:37:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750828AbdBWRhG (ORCPT ); Thu, 23 Feb 2017 12:37:06 -0500 Received: from kitenet.net ([66.228.36.95]:37228 "EHLO kitenet.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751169AbdBWRhE (ORCPT ); Thu, 23 Feb 2017 12:37:04 -0500 X-Question: 42 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=joeyh.name; s=mail; t=1487871407; bh=ic5XPi/6+ingyJh9AHM2CmPnKTKWit/d4G0jXpEnOmQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hTqyVshSYtL4HZH0NKm1YscN8Lrhukc6oZd1HHi4sRW6jC7/f1LxWCBz0zqHmPkcs l6mcTqWM2G9kN8Yt0OuQ8kuT5wExbuzAntwNgMrB7hOMXPry2OvA9g2DLUbR5rKE6I Bhc3p63Fe63LhPgAod1x5ggTvxxMI05U6cQ8Y8PA= DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=joeyh.name; s=mail; t=1487871347; bh=ic5XPi/6+ingyJh9AHM2CmPnKTKWit/d4G0jXpEnOmQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SASSfG9BmyaAQuNnc+k1Rd7s4dE1BJhtsnXNOV5OTA6bibELOJZvffG7b5bQLzSOL e0CvviL9beEwQGBIJWDW6AT/MhjH8jzweZpDaZl1Xakj1EJL2FwgVDruZxnWcEI20W 7ThaBTSWFN5mlsY7J/UgWQJP2AEFVsBL8v4xV664= Date: Thu, 23 Feb 2017 13:35:47 -0400 From: Joey Hess To: Junio C Hamano Cc: Git Mailing List Subject: Re: SHA1 collisions found Message-ID: <20170223173547.qljypk7sdqi37oha@kitenet.net> References: <20170223164306.spg2avxzukkggrpb@kitenet.net> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ycj5mvo4eznpkhsi" Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20161126 (1.7.1) Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org --ycj5mvo4eznpkhsi Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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. >=20 > That may be true, but > https://public-inbox.org/git/Pine.LNX.4.58.0504291221250.18901@ppc970.osd= l.org/ That's about someone replacing an valid object in Linus's repository with an invalid random blob they found that collides. This SHA1 break doesn't allow generating such a blob anyway. Linus is right, that's an impractical attack. Attacks using this SHA1 break will look something more like: * I push a "bad" object to a repo on github I set up under a pseudonym. * I publish a "good" object in a commit and convince the maintainer to merge it. * I wait for the maintainer to push to github. * I wait for github to deduplicate and hope they'll replace the good object with the bad one I pre-uploaded, thus silently changing the content of the good commit the maintainer reviewed and pushed. * The bad object is pulled from github and deployed. * The maintainer still has the good object. They may not notice the bad object is out there for a long time. Of course, it doesn't need to involve Github, and doesn't need to rely on internal details of their deduplication[1];=20 that only let me publish the bad object under a psydonym. --=20 see shy jo [1] Which I'm only guessing about, but now that we have colliding objects, we can upload them to different repos and see if such dedupication happens. --ycj5mvo4eznpkhsi Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEE6FpfY7MdJMHr8NgcyRDZIiUS48cFAlivHXEACgkQyRDZIiUS 48dYIw//ariVxwkyBr5LHucunYQS1hCturaUDJ9BO0Ow5eISFDOEsWnMzaP/La6n f91TxsmddrUWKT8+/HJsNITWYyhzt07TLjJvvRpJH35IYOVZe6915FUf9mvTulWN eWoApm5/kXi7DzFJZ+5zdlIlYhfxtWl36OQ732Tk0zS9F23I7m8FAB1vtCK6ixe7 u+5enYkWVQcK/E+mDZFAg/DNntjGdduFQki6iK3TUXz2aZg/EHH0Ze1WoN4FS0xE PH3Y7zuHrZEt/OiApyWE2P5IUeXMgPbCAKRyCt/qkLbr+lIFiGoOez3f0wh9UBHW CSAi1w0YPLCbpvfvrjiwbxpuLRcZdg2CNHfnXba2qagj9jZeNVZcefylvJKHiyQK gWnPb0T3egv+bxrkR7oy9L6EVbQTYxLgEs0jjbrgc3NPcCxSPHaun0L42aHUHndJ yZuCPm8xudhoGLBG0VyyUonYXirNZybQoNHvFE1ScdyTa2ZF0Pl3FIJuOTua/RfB dZhyGuMZc4C/1eQ0nYf/Pli8hZXcI0oV/XEAakljdoGYcHJHglLmqdhuJw6NAq2T QAGiNa2Lcyv4le6j/598m2IcnaR1UPep5FfUuTUIgL4deTMN7ivQnnXTm7kdhX+a ghBXhIsK2u1xiBgNe0G42YLHnu1p918XLvAvwcznb7OHIP/sNaA= =o5lN -----END PGP SIGNATURE----- --ycj5mvo4eznpkhsi--