From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 17 Aug 2001 03:56:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 17 Aug 2001 03:56:43 -0400 Received: from nef.ens.fr ([129.199.96.32]:14599 "EHLO nef.ens.fr") by vger.kernel.org with ESMTP id ; Fri, 17 Aug 2001 03:56:34 -0400 Date: Fri, 17 Aug 2001 09:56:27 +0200 From: Thomas Pornin To: ehaase@inf.fu-berlin.de Cc: linux-kernel@vger.kernel.org Subject: Re: ext2 not NULLing deleted files? Message-ID: <20010817095627.A15129@bolet.ens.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <01081709381000.08800@haneman> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org In article <01081709381000.08800@haneman> you write: > "The Other OS" in its professional version does of course clear the > deleted blocks with 0's for security reasons That's not much more than a smoke screen, actually. Wiping out data from a disk requires more than merely writing 0's, if the bad guy is assumed to physically have hold of the disk. See, for instance, the paper from Peter Gutmann, "Secure Deletion of Data from Magnetic and Solid-State Memory" (published in Usenix'96). Such games are much dependant on the actual writing technology, and harddisk cache (which cannot be deacticated on some modern IDE disks) gets in the way. Besides, performance is terrible (if you need to rewrite seven times a file with different patterns for each deletion, imagine what happens when you delete a 100 MBytes file...). The only truly secure way to do is encryption: if all data that gets to the disk is encrypted, physical details about the disk are unimportant, so security cannot be compromised by some smarter physicist with more expensive tools. --Thomas Pornin