From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: About git and the use of SHA-1 Date: Tue, 29 Apr 2008 22:47:00 -0700 Message-ID: <20080430054700.GA1345@old.davidb.org> References: <7f9d599f0804290859y6a579302m5db9f7f827b320a4@mail.gmail.com> <7f9d599f0804291048n2c706f3amdf159ffe86bdbc8@mail.gmail.com> <7f9d599f0804291102j4a30c344h18d12d03a6d5953b@mail.gmail.com> <7f9d599f0804291331v2f44bee1y29c1580d68a3107a@mail.gmail.com> <46a038f90804291958u14eddc49sb54c7fd4a3a10381@mail.gmail.com> <7f9d599f0804292218x7d94d7del20d4d48bbad80fb5@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Cc: Martin Langhoff , Daniel Barkalow , Nicolas Pitre , Andreas Ericsson , Dmitry Potapov , Henrik Austad , git@vger.kernel.org To: Geoffrey Irving X-From: git-owner@vger.kernel.org Wed Apr 30 07:48:13 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 1Jr5Am-0006UF-1M for gcvg-git-2@gmane.org; Wed, 30 Apr 2008 07:48:08 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755867AbYD3FrN (ORCPT ); Wed, 30 Apr 2008 01:47:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753645AbYD3FrM (ORCPT ); Wed, 30 Apr 2008 01:47:12 -0400 Received: from mail.davidb.org ([66.93.32.219]:48093 "EHLO mail.davidb.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753172AbYD3FrL (ORCPT ); Wed, 30 Apr 2008 01:47:11 -0400 Received: from davidb by mail.davidb.org with local (Exim 4.69 #1 (Debian)) id 1Jr59g-0000PP-6S; Tue, 29 Apr 2008 22:47:00 -0700 Mail-Followup-To: Geoffrey Irving , Martin Langhoff , Daniel Barkalow , Nicolas Pitre , Andreas Ericsson , Dmitry Potapov , Henrik Austad , git@vger.kernel.org Content-Disposition: inline In-Reply-To: <7f9d599f0804292218x7d94d7del20d4d48bbad80fb5@mail.gmail.com> User-Agent: Mutt/1.5.16 (2007-06-09) 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 10:18:55PM -0700, Geoffrey Irving wrote: >> 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. usertime and realtime are from the start of the invocation of the postscript interpreter, not based on the outside world. So, the interpreter could wait arbitrarily long, but has no way of knowing any external reference to time. I could imagine trickery with PDF signatures and their expiration times, but you shouldn't be able to do anything with the information, so it would be an exploit, and would probably be fixed. David