Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751659AbXLIMcZ (ORCPT ); Sun, 9 Dec 2007 07:32:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750801AbXLIMcQ (ORCPT ); Sun, 9 Dec 2007 07:32:16 -0500 Received: from thunk.org ([69.25.196.29]:41471 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750789AbXLIMcP (ORCPT ); Sun, 9 Dec 2007 07:32:15 -0500 Date: Sun, 9 Dec 2007 07:31:47 -0500 From: Theodore Tso To: Ismail =?iso-8859-1?Q?D=F6nmez?= Cc: Adrian Bunk , Bill Davidsen , Marc Haber , linux-kernel@vger.kernel.org Subject: Re: Why does reading from /dev/urandom deplete entropy so much? Message-ID: <20071209123147.GZ17037@thunk.org> Mail-Followup-To: Theodore Tso , Ismail =?iso-8859-1?Q?D=F6nmez?= , Adrian Bunk , Bill Davidsen , Marc Haber , linux-kernel@vger.kernel.org References: <20071204114125.GA17310@torres.zugschlus.de> <200712090010.10362.ismail@pardus.org.tr> <20071208234612.GQ17037@thunk.org> <200712090821.16483.ismail@pardus.org.tr> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <200712090821.16483.ismail@pardus.org.tr> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on thunker.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 939 Lines: 19 On Sun, Dec 09, 2007 at 08:21:16AM +0200, Ismail D?nmez wrote: > My understanding was if you can drain entropy from /dev/urandom any futher > reads from /dev/urandom will result in data which is not random at all. Is > that wrong? Past a certain point /dev/urandom will stat returning results which are cryptographically random. At that point, you are depending on the strength of the SHA hash algorithm, and actually being able to not just to find hash collisions, but being able to trivially find all or most possible pre-images for a particular SHA hash algorithm. If that were to happen, it's highly likely that all digital signatures and openssh would be totally broken. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/