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Re: [debian-knoppix] Re: Secure Deleting


On Wed, Nov 06, 2002 at 05:32:56PM +0100, Nils Magnus wrote:
> Hi,
> On the matter of secure deleting:
[ ... ]
> New files with zeroes is not a good idea. I recommend everyone to get
> yourself a picture of a raster-ray-microscope in the magnectic spectrum
> to see what is left after such attemps ... You most probably don't want
> to write files to journaled partions if you need to delete them in a
> secure manner on a by-file basis.
> However, if your systems are not journaled, the dd-method is not too
> bad, if you aren't too paranoid. Be sure to use if=/dev/urandom instead
> of /dev/zero or /dev/random.

I haven't handled the raster-ray-microscope but I don't think there's
a big difference in using 0's or random bits if you only overwrite the
data once. Your argument goes that writing 0s or 1s is insecure as you
can see traces of the old value under the microscope. The same is
possible with random data, as you know the new value. It's only more
work as the known new data isn't the same everywhere. I'd say writing
random data twice or more times could be secure.

> ///Nils

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