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Re: Peter Gutmann data deletion theaory?
From: Volker Tanger <vtlists () wyae de>
Date: Fri, 22 Jul 2005 10:14:15 +0200


On Thu, 21 Jul 2005 14:07:12 -0500
Simple Nomad <thegnome () nmrc org> wrote:
On Wednesday 20 July 2005 18:48, Jared Johnson wrote:
Data overwritten once or twice
The quote is from 1996. I spoke with Guttman about this at AusCERT a
few years  ago and even *he* doesn't believe it anymore. Drive
technology has changed  substantially since then.

His theory no longer does hold true. His 1996 paper is available at
http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html, targeting
MFM and RLL disk technology, where a typical 5.25" disk held 20-80MB
(yes, MEGAbyte, not GB). His recommendations were based on old magnetic
disc technology where each bit was represented by the magnetical
orientation on the platter (north=1, south=0). After that came other
technologies, where bits are defined by changes of the magnetic field
even down to probabilistic field measurements - which allowes tighter
data packing but rendered the base of his recommendations useless.

Of course - if you write often enough with different data over "the
same" spot, the original data will become more and more unreadable.

OTOH I have seen one company with a *really* thorough disk & tape 
cleaning technique: 

        1. writing zeroes all over
        2. low level format
        3. shredding the disc drive into small pieces
        4. magnet treatment of the scrap metal
        5. burning in their own waste incinerating plant

For "home use" a grinder/raw polish/sandblast treatment of both platter
sides should be fine, too...   ;-)




Volker Tanger    http://www.wyae.de/volker.tanger/
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