From owner-freebsd-questions@FreeBSD.ORG Wed Feb 18 03:51:18 2015 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id DBF9C211 for ; Wed, 18 Feb 2015 03:51:18 +0000 (UTC) Received: from mail-ob0-x230.google.com (mail-ob0-x230.google.com [IPv6:2607:f8b0:4003:c01::230]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 96473328 for ; Wed, 18 Feb 2015 03:51:18 +0000 (UTC) Received: by mail-ob0-f176.google.com with SMTP id wo20so61131887obc.7 for ; Tue, 17 Feb 2015 19:51:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:date:from:user-agent:mime-version:to:subject:references :in-reply-to:content-type:content-transfer-encoding; bh=X6I+JG57QVkkn+dL2JaxoSibiVUvLOZFbiCbSoL+a24=; b=wfGKW1d23I64+KQZN9jO2KBylvcmk5Xo62+IgPOXpk5sRweNZrb9ibhjfp2fUWvx9g /H3DfsrTJe7IBEAN4LDylajyj3A8eCrRdbuDjEPxpvzNrUlHwJnCyYTT8TaYHkPgD/YJ +4FbWADjIGW5sYoKCcgKDlq1Ko7BlLyZQTnhXwhYnuiyEm8HyRypPOvq7UIe0T1/RgSp UmSYsEFaTb3l4IX3rYBif9IpQLUfn6GnElAouQ5zVSN1Qu8gxSsGMfh4GQwSokt2HNc1 FEmWlKu/bubevvnh4fdDwolh+YZ4781jQ4dkFt3qtVNdUJyO0msLqLx053LXr2SxA0Oj 49Rw== X-Received: by 10.182.101.133 with SMTP id fg5mr20707729obb.41.1424231477895; Tue, 17 Feb 2015 19:51:17 -0800 (PST) Received: from localhost.localdomain (ip-64-134-6-77.public.wayport.net. [64.134.6.77]) by mx.google.com with ESMTPSA id m64sm12367913oik.20.2015.02.17.19.51.16 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Feb 2015 19:51:16 -0800 (PST) Message-ID: <54E40C33.1030600@gmail.com> Date: Tue, 17 Feb 2015 20:51:15 -0700 From: jd1008 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: freebsd-questions@freebsd.org Subject: Re: [Bulk] Re: What's in my hard drive? How can I get rid of it? References: <54E39F83.70002@gmail.com> <51803.128.135.70.2.1424219858.squirrel@cosmo.uchicago.edu> <20150218020243.366fe968@archlinux> In-Reply-To: <20150218020243.366fe968@archlinux> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 18 Feb 2015 03:51:18 -0000 On 02/17/2015 06:02 PM, Ralf Mardorf wrote: > On Tue, 17 Feb 2015 18:37:38 -0600 (CST), Valeri Galtsev wrote: >> On Tue, February 17, 2015 5:30 pm, Daniel Feenberg wrote: >>> >>> On Tue, 17 Feb 2015, Michael Powell wrote: >>> >>>> jd1008 wrote: >>>> >>>> [snip] >>>> >>>> Remove the cover. Remove the platters. Smash all platters with large >>>> sledge >>>> hammer until all pieces are fairly small. Melt material with >>>> oxyacetylene >>>> welders torch. Repeat smashing with hammer. Soak for few hours in >>>> hydrofluoric acid. Rinse and allow to dry. Grind material into a >>>> fine particulate dust. Dispose of out the back of airplane while >>>> flying or drop >>>> into convenient nearby volcano. That might be good enough. >>>> >>>> Send the electronic components to Kaspersky for analysis. >>> I did once investigate claims that overwritten sectors could be read >>> by sophisticated instruments and posted my results at: >>> >>> http://www.nber.org/sys-admin/overwritten-data-gutmann.html >>> >>> >>> In short - that is pure science fiction. >>> >> Interesting. I never saw this particular explanation. I have heard that >> overwiritten data can be recovered (to significant extent). Due to >> different reason. I lost the reference, so let me try to reproduce what >> I've read (and that didn't and still doesn't offend my university >> degree knowledge, physics was part of it): >> >> If some information sits intact for years (that is without any change >> in particular physical places on disk platters), then over time due to >> some sort of aging magnetic domains become slightly different (in >> size, maybe?) in places where magnetization is in one direction from >> that in the other direction. If to overwrite that information, nothing >> original becomes readable. If, however you magnetize the whole bulk of >> platter in one direction, then the areas that were magnetized for very >> long time in one direction have slightly different residual >> magnetization from areas magnetized for long time in different >> direction. This difference is much smaller that sensitivity of regular >> drive magnetic heads and pre-amlifier. However, more sensitive >> equipment is capable to detect that thus very significant portion of >> information can be recovered (not 100% though). You can recover >> information even if it was overwritten with some new junk, provided >> this junk didn't sit there comparably long. >> >> One still can fully wipe the information, even sitting there due to >> those "aged magnetic domains" if one re-magnetizes platters in opposite >> directions many times (over 1000) going deeply into hysteresis every >> time. One time overwriting data is definitely not enough. Using some >> 50-100 cycles may not be sufficient either (but already this number of >> cycles becomes impractical with all software based destroying of >> information). >> >> Sorry about long e-mail. Sledge hammer and shredder are the best for >> the purpose ;-) > Actually criminal investigation departments seems to be unable to > recover all the data that was deleted by a simple rm command, even on > journaling file systems. Why is it recommended to mount read only, as > soon as possible, if we lose data, to be able to recover that data? > > The NSA is able to recover all the data that was deleted all over the > world even by a shred command on a non-journaling FS? If so, the NSA > isn't willing to give hints against child molesters and other criminals, > because the NSA is the watchdog of more important crimes? That's > grotesque. Well, you have to admit - they do have priorities :) Self interest overrules all other interests.