From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id 6B2BE138D14 for ; Sun, 12 Jul 2015 19:14:15 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 28E4AE08E1; Sun, 12 Jul 2015 19:14:09 +0000 (UTC) Received: from mail-qk0-f195.google.com (mail-qk0-f195.google.com [209.85.220.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id D96CAE0874 for ; Sun, 12 Jul 2015 19:14:07 +0000 (UTC) Received: by qkbs7 with SMTP id s7so1386629qkb.3 for ; Sun, 12 Jul 2015 12:14:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:sender:in-reply-to:references:date:message-id:subject :from:to:content-type; bh=QVUmz00lcQfTZFtQXZbJVbrRFpkE3oEEBIgGlnEs99I=; b=WDyZYSwGHM7uHGWx6+c36cb5HETmQDBIezVNEH7wHHRifSytVSSzTI4so6duBgPFUX 7evdT7FrItHEx1mFdWLzmejanNo9SJfX/OItANrYuPBKK5gKauquvAsazz+IBhLS9AXz 2i+3/hA5oU1VkafrR16FLEAu/UgEXc8BJyf8HNxTbGFmXUjDEpKvwpi4od/Z2FSM17Eb Fj5aHEhpilrZsXuru2Eu/cPAS5yuwj79EYJ3xMKnFqstcBoOc+GKX9gdnP26Rwgct/ug dKBhDAN6B9+aG1t/+ougIXVtkcoJBbTlmlCDzeZLOnwRLM1jFKIkCLzPqRS5riqsTbjM DvoQ== Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 X-Received: by 10.140.85.85 with SMTP id m79mr48886696qgd.37.1436728447277; Sun, 12 Jul 2015 12:14:07 -0700 (PDT) Sender: freemanrich@gmail.com Received: by 10.140.34.68 with HTTP; Sun, 12 Jul 2015 12:14:07 -0700 (PDT) In-Reply-To: <55A296A7.5070301@googlemail.com> References: <20150712143525.07b6bdf5@thetick> <55A296A7.5070301@googlemail.com> Date: Sun, 12 Jul 2015 15:14:07 -0400 X-Google-Sender-Auth: cjKz-FIPnfHJ-vABMvCYAI5Cm4w Message-ID: Subject: Re: [gentoo-user] Securely deletion of an HDD From: Rich Freeman To: gentoo-user@lists.gentoo.org Content-Type: text/plain; charset=UTF-8 X-Archives-Salt: a7294ad2-bfdc-4af4-8789-defed9a084a2 X-Archives-Hash: 39e237baabd88a28e9890020ef612516 On Sun, Jul 12, 2015 at 12:32 PM, Volker Armin Hemmann wrote: > > actually 1 time is enough. With zeros. Or ones. Does not matter at all. > That depends on your threat model. If you're concerned about somebody reading the contents of the drive using the standard ATA commands, then once with zeros is just fine. Secure erase is probably easier/faster. If you're concerned about somebody removing the disks from the drive and reading them with specialized equipment then you really want multiple rounds of complete overwrites with random data. Even then you run the risk of relocation blocks and all that stuff, so the secure erase at the end is still a wise move but it may or may not completely do the job. If you're concerned about somebody leaving the disks in the drive but having access to directly manipulate the drive heads to possibly access data not accessible using the standard ATA commands then one pass is probably good enough, but I'd still use random data instead of zeros. The reason is that a clever firmware (especially on an SSD) might not actually record zeros to the regular disk space, but instead just mark the block range as containing zeros, leaving the actual data intact. For random data the drive has to actually store the contents as it cannot be represented in any more concise way. If I'm not in a rush I prefer to just do the multiple passes. Why take a chance? And of course full-disk encryption is the solution to all of the above, as it defeats any kind of attack at the level of the drive and is proactive in nature. -- Rich