From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760277AbXE2PRi (ORCPT ); Tue, 29 May 2007 11:17:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750876AbXE2PRa (ORCPT ); Tue, 29 May 2007 11:17:30 -0400 Received: from an-out-0708.google.com ([209.85.132.249]:46781 "EHLO an-out-0708.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751202AbXE2PRa (ORCPT ); Tue, 29 May 2007 11:17:30 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=B172ubJudrAGC1lpwLLoQEOuDR9I2tO8rwRJrz1j56f45kVFxQLWniWyGkYRLUf5GnfEHIFBPKLN3NZEQcmraIgSlveq3DHtV7VRgh7nEcumsybAVKkCB45BGNCVHjNM58+P3f7XL33x5ALadZ7wYDb6Z6WeQwRW+Mrlu/r9XD4= Message-ID: Date: Tue, 29 May 2007 16:17:24 +0100 From: "M Macnair" To: "Pavel Machek" Subject: Re: Seeding /dev/random not working Cc: "Theodore Tso" , linux-kernel@vger.kernel.org In-Reply-To: <20070529141456.GC5840@ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20070529131501.GA9899@thunk.org> <20070529141456.GC5840@ucw.cz> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 5/29/07, Pavel Machek wrote: > Hi! > > > > I have two embedded boards (one ARM, one PowerPC), running two > > > different versions of 2.6. They have no hard drives, keyboards or > > > mice. They each have a NIC, but I understand these make no > > > contribution to the entropy pool. > > > > > > if [ -f $random_seed ]; then > > > cat $random_seed >/dev/urandom # should seed the pool > > > fi > > > dd if=/dev/urandom of=$random_seed count=1 2>/dev/null # save some > > > data from urandom for next boot > > > > > > I have rebooted my boards many times, and after each boot I read the > > > contents of $random_seed. Whilst it does not happen every time, the > > > contents of $random_seed are /often the same/. To give you a feel: > > > rebooted 11 times, got a total of 3 different outputs. > > > > Ok, so this is telling me a couple of things. First of all, if you're > > only getting three outputs, it means that you don't have any > > peripherals feeding entropy into the system from the boot sequence. > > Without any hard drives, keyboards or mice, and a NIC whose device > > driver hasn't been configured to feed entropy, you're definitely > > hosed. > > Can we get at least time-of-boot from rtc clock to the pool? We really > should not be getting identical outputs... Ah yes that is one thing I forgot to mention - when you turn these boards off, you really do turn them off - no battery means no clock. They wake up every time in 1970. I am planning on providing my own entropy to this system by feeding /dev/random (which leads to the problem of it not working...).