From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754822AbXLDQSZ (ORCPT ); Tue, 4 Dec 2007 11:18:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752967AbXLDQSR (ORCPT ); Tue, 4 Dec 2007 11:18:17 -0500 Received: from mailout.stusta.mhn.de ([141.84.69.5]:41693 "EHLO mailhub.stusta.mhn.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752925AbXLDQSR (ORCPT ); Tue, 4 Dec 2007 11:18:17 -0500 Date: Tue, 4 Dec 2007 17:18:11 +0100 From: Adrian Bunk To: Marc Haber Cc: linux-kernel@vger.kernel.org Subject: Re: Why does reading from /dev/urandom deplete entropy so much? Message-ID: <20071204161811.GB15974@stusta.de> References: <20071204114125.GA17310@torres.zugschlus.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20071204114125.GA17310@torres.zugschlus.de> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 04, 2007 at 12:41:25PM +0100, Marc Haber wrote: > While debugging Exim4's GnuTLS interface, I recently found out that > reading from /dev/urandom depletes entropy as much as reading from > /dev/random would. This has somehow surprised me since I have always > believed that /dev/urandom has lower quality entropy than /dev/random, > but lots of it. man 4 random > This also means that I can "sabotage" applications reading from > /dev/random just by continuously reading from /dev/urandom, even not > meaning to do any harm. > > Before I file a bug on bugzilla, >... The bug would be closed as invalid. No matter what you consider as being better, changing a 12 years old and widely used userspace interface like /dev/urandom is simply not an option. > Greetings > Marc cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed