Subj : Why Zeroing Disks Doesn't Work
To   : All
From : warmfuzzy
Date : Mon Jul 02 2018 20:50:08

You might have heard about "secure deletion" of hard drives before they are
repurposed in giving them to charities or sold for a bit of cash.  One of the
most used "algorithms" is a simple "zeroing" of a disk where all the same
"character" is used to fill the whole drive.  The problem with this is its
not random, but rather a universal wipe of the whole drive with a single
element.  Because of this the information is still there on the drive, its
just offset a bit, so to recover the stuff on the disk you would just need to
remove the "shift" of characters and the original content reappears.  You see
using a single character to wipe a drive with means that it offsets the data
by a "known" element, and simply correcting for that character reveals what
was previously on that hard drive.  I suggest using eight passes of a
pseudo-random number generator (PRNG).

Something to think about.

-wf

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