Date: Tue, 17 Feb 2015 20:51:15 -0700 From: jd1008 <jd1008@gmail.com> To: freebsd-questions@freebsd.org Subject: Re: [Bulk] Re: What's in my hard drive? How can I get rid of it? Message-ID: <54E40C33.1030600@gmail.com> In-Reply-To: <20150218020243.366fe968@archlinux> References: <54E39F83.70002@gmail.com> <mc0ad5$qu2$1@ger.gmane.org> <alpine.LRH.2.11.1502171829280.7759@sas1.nber.org> <51803.128.135.70.2.1424219858.squirrel@cosmo.uchicago.edu> <20150218020243.366fe968@archlinux>
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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.
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