[Dshield] Secure Data Removal
josh at raintreeinc.com
Fri Jun 4 15:34:57 GMT 2004
As with all things digital, measurements are made, and a threshold is
determined to mark the difference between a 1 and a 0. For instance, in
digital circuits, a potential of more than some predetermined voltage is
a 1, and anything else is a 0. Although voltages of the actual signals
vary, as long as all the "1" signals are greater than the given voltage
and the "0" signals are less than it, your signal remains wholly intact.
Which is indeed why digital reproduction of analog data is so much
closer to the real thing than analog reproduction in most cases -- the
signal can be distorted quite a lot and still remain on the proper side
of that threshold value, so the signal remains unchanged.
When you overwrite a hard drive with all 0's, you change the strength of
the magnetism of each bit on the drive to something less than a
particular threshold. Picture the magnetic strength of each spot on the
drive as though it were drawn on a graph, with 1's as peaks and 0's as
valleys -- you've just gone and pushed the graph down a few notches so
that the entire drive, peaks and valleys alike, are all below that
threshold value. But there are still peaks and valleys, they're just not
as big. If you can read those peaks and valleys, you can still recover
Raintree Systems, Inc.
760 509 9000
> -----Original Message-----
> From: Christophe Rome <asrgchr at yahoo.com>
> To: list at lists.dshield.org
> Date: Fri, 4 Jun 2004 04:23:01 -0700 (PDT)
> Subject: [Dshield] Secure Data Removal
>>A while ago there was a small topic about secure data
>>removal on this list. I remember that overwriting an
>>entire hard drive with O's would erase it completely
>>in a FAST way but NOT a SECURE way. I was wondering
>>now how one could be able to retrieve data from a hard
>>drive that has been completely overwritten with 0's?
>>Or is my assumption wrong?
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