From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932074AbWEPPEc (ORCPT ); Tue, 16 May 2006 11:04:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932070AbWEPPEb (ORCPT ); Tue, 16 May 2006 11:04:31 -0400 Received: from zcars04e.nortel.com ([47.129.242.56]:46063 "EHLO zcars04e.nortel.com") by vger.kernel.org with ESMTP id S932066AbWEPPE3 (ORCPT ); Tue, 16 May 2006 11:04:29 -0400 Message-ID: <4469E9ED.4010700@nortel.com> Date: Tue, 16 May 2006 09:04:13 -0600 From: "Christopher Friesen" User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040115 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Pavel Machek CC: Kyle Moffett , Muli Ben-Yehuda , Alan Cox , Jonathan Day , linux-kernel@vger.kernel.org, Zvika Gutterman Subject: Re: /dev/random on Linux References: <20060515213956.31627.qmail@web31508.mail.mud.yahoo.com> <1147732867.26686.188.camel@localhost.localdomain> <20060516025003.GC18645@rhun.haifa.ibm.com> <20060516124637.GB6654@elf.ucw.cz> In-Reply-To: <20060516124637.GB6654@elf.ucw.cz> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 16 May 2006 15:04:16.0549 (UTC) FILETIME=[0019DD50:01C678FA] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Pavel Machek wrote: >>I was unsure about the purported forward-security-breakage claims >>because I don't know how to validate those, but I seem to recall >>(from personal knowledge and the paper) that the kernel does an SHA1 >>hash of the contents of the pool and the current cycle-counter when >>reading, uses that as input for the next pool state and returns it >>as /dev/random output. Since the exact cycle-counter value is never >>exposed outside the kernel and only a small window of the previous > > > Are you sure? For vsyscalls to work, rdtsc has to be available from > userspace, no? I suspect he means "the exact cycle counter value at the time of reading the contents of the pool" is never exposed outside the kernel. "rdtsc" is of course available in userspace on x86. Chris