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Re: Peter Gutmann data deletion theaory?
From: Dana Hudes <dhudes () tcp-ip info>
Date: Thu, 21 Jul 2005 20:31:08 -0400 (EDT)

The NSA disagree and have conducted laboratory tests.
I work for NYC as a unix admin (Solaris). We use the sun format purge to 
erase disks (that can be written to; drives that won't spin up or can't be 
written are another problem).

I guarantee that a sufficiently strong degausser will erase your 
data...along with the timing tracks and possibly burning out micromotors 
and ball bearings. Its a question of how many oersteds you need for the 
drive so that the magnetic field penetrates the housing (take out the 
platters and you have another situation entirely).

I don't have the site bookmarked at home but NIST or NSA have a site which 
reviews the degaussing equipment and other data erasure techniques.

On Wed, 20 Jul 2005, Jared Johnson wrote:


Do you all agree with Peter Gutman's conclusion on his theory that data can
never really be erased, as noted in his quote below:

"Data overwritten once or twice may be recovered by subtracting what is
expected to be read from a storage location from what is actually read. Data
which is overwritten an arbitrarily large number of times can still be
recovered provided that the new data isn't written to the same location as
the original data (for magnetic media), or that the recovery attempt is
carried out fairly soon after the new data was written (for RAM). For this
reason it is effectively impossible to sanitise storage locations by simple
overwriting them, no matter how many overwrite passes are made or what data
patterns are written. However by using the relatively simple methods
presented in this paper the task of an attacker can be made significantly
more difficult, if not prohibitively expensive."

It seems that the perhaps the only real way to rid your Hard Drives of data
is to burn them. 

I'd love to hear some thoughts on this from security and data experts out

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