From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 21 Aug 2001 08:40:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 21 Aug 2001 08:40:39 -0400 Received: from shed.alex.org.uk ([195.224.53.219]:4584 "HELO shed.alex.org.uk") by vger.kernel.org with SMTP id ; Tue, 21 Aug 2001 08:40:37 -0400 Date: Tue, 21 Aug 2001 13:40:50 +0100 From: Alex Bligh - linux-kernel Reply-To: Alex Bligh - linux-kernel To: Marco Colombo , Alex Bligh - linux-kernel Cc: David Wagner , linux-kernel@vger.kernel.org, Alex Bligh - linux-kernel Subject: Re: /dev/random in 2.4.6 Message-ID: <1467527.998401250@[169.254.79.209]> In-Reply-To: In-Reply-To: X-Mailer: Mulberry/2.1.0b3 (Win32) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > A little question: I used to believe that crypto software requires > strong random source to generate key pairs, but this requirement in > not true for session keys. You don't usually generate a key pair on > a remote system, of course, so that's not a big issue. On low-entropy > systems (headless servers) is /dev/urandom strong enough to generate > session keys? I guess the little entropy collected by the system is > enough to feed the crypto secure PRNG for /dev/urandom, is it correct? I /think/ the answer is 'it depends'. a) If 'low entropy' meant 'no entropy', then the seed would be the same booting one system as on a black-hat identical system. b) If you can obtain (one way or another) a session key, you can hijack that session. Whether or not you can then intercept other sessions depends in part what that session is (if, for instance, it is a root ssh session...). If you reduce the search space for session keys, you make being able to hijack a session considerably easier. -- Alex Bligh