From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Geoffrey Irving" Subject: Re: About git and the use of SHA-1 Date: Tue, 29 Apr 2008 22:18:55 -0700 Message-ID: <7f9d599f0804292218x7d94d7del20d4d48bbad80fb5@mail.gmail.com> References: <200804281829.11866.henrikau@orakel.ntnu.no> <7f9d599f0804290859y6a579302m5db9f7f827b320a4@mail.gmail.com> <7f9d599f0804291048n2c706f3amdf159ffe86bdbc8@mail.gmail.com> <7f9d599f0804291102j4a30c344h18d12d03a6d5953b@mail.gmail.com> <7f9d599f0804291331v2f44bee1y29c1580d68a3107a@mail.gmail.com> <46a038f90804291958u14eddc49sb54c7fd4a3a10381@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Daniel Barkalow" , "Nicolas Pitre" , "Andreas Ericsson" , "Dmitry Potapov" , "Henrik Austad" , git@vger.kernel.org To: "Martin Langhoff" X-From: git-owner@vger.kernel.org Wed Apr 30 07:20:05 2008 connect(): Connection refused Return-path: Envelope-to: gcvg-git-2@gmane.org Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1Jr4ja-0007GO-20 for gcvg-git-2@gmane.org; Wed, 30 Apr 2008 07:20:02 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753383AbYD3FS6 (ORCPT ); Wed, 30 Apr 2008 01:18:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752406AbYD3FS6 (ORCPT ); Wed, 30 Apr 2008 01:18:58 -0400 Received: from rv-out-0708.google.com ([209.85.198.247]:34161 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752686AbYD3FS5 (ORCPT ); Wed, 30 Apr 2008 01:18:57 -0400 Received: by rv-out-0506.google.com with SMTP id k29so187787rvb.1 for ; Tue, 29 Apr 2008 22:18:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; bh=tTgBbmvyLwnXtbTi3sSX20UwbCQeDPqM5fTLZIxJQ6A=; b=RUF5/vqUJzJSJxov7qmZDPM82lnPweij0APSOAPyqncMPScTSUppFCXmS6y9qk0bujOX6AdVHXmTnv+RBB7OahxGhQNYwPEPMjD/Lt9cOWR4WWdbiNFFZXzfF948Vn5v+FaizWzE1TD2gIBqPyuEcQ79Wh5djGthe0CXIvkYUrk= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=Ht7o4OX8zz/CM6dFrVelzVoUA74rvEYV2epS3AQh5+aCh/oRRPkPvzCKaWty9tdorlKgeVoUkza7ADskWJlvde/Q49BKPIoChAbNELN6pzRL6i63E2km34ezwImaO/DdIF324laTmIL35WrC75FYaZdEsmlHUrWrhgC0Jvg86vc= Received: by 10.140.169.4 with SMTP id r4mr125127rve.131.1209532735395; Tue, 29 Apr 2008 22:18:55 -0700 (PDT) Received: by 10.140.178.16 with HTTP; Tue, 29 Apr 2008 22:18:55 -0700 (PDT) In-Reply-To: <46a038f90804291958u14eddc49sb54c7fd4a3a10381@mail.gmail.com> Content-Disposition: inline X-Google-Sender-Auth: fbf4f978281e26a1 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: On Tue, Apr 29, 2008 at 7:58 PM, Martin Langhoff wrote: > On Wed, Apr 30, 2008 at 8:31 AM, Geoffrey Irving wrote: > > I sincerely hope that pdf/postscript don't allow the internal > > rendering code to branch based on the current date. That would be an > > absurd security hole, and would indeed make you entirely correct. If > > PS is Turing complete, and does know about dates. So yes, you can make > such conditionals. I knew postscript was Turing complete, but had (naively) assumed it executed sandboxed and deterministically and would therefore display uniformly barring interpreter bugs. Looking over the spec, I can't find where it's possible to read the current date, but the usertime/realtime variables are sufficient as long as the attacker knows how fast the relevant machines are. > That original md5 paper with the 2 PDF files is mainly a good example > that you should trust binary blobs, that's all. The md5 trick is a > nice demo, but misses the point entirely. > > I can't find it now, but someone had written a PDF file that printed > Pi computing in inside the PS VM. The tiny file would keep the printer > churning out paper until it ran out of memory. :-) According to wikipedia, PDF doesn't have conditionals or loops of any kind, so you probably mean a postscript file. Geoffrey