mailing list archives
RE: Peter Gutmann data deletion theaory?
From: "dave kleiman" <dave () isecureu com>
Date: Sun, 24 Jul 2005 15:30:30 -0400
Here is a quote directly from Peter I received Saturday, he asked to have it
passed on to the list.
I'd love to hear some thoughts on this from security and data experts
People should note the epilogue to the paper:
In the time since this paper was published, some people have treated the
pass overwrite technique described in it more as a kind of voodoo
incantation to banish evil spirits than the result of a technical analysis
of drive encoding techniques. As a result, they advocate applying the
voodoo to PRML and EPRML drives even though it will have no more effect
a simple scrubbing with random data. In fact performing the full 35-pass
overwrite is pointless for any drive since it targets a blend of scenarios
involving all types of (normally-used) encoding technology, which covers
everything back to 30+-year-old MFM methods (if you don't understand that
statement, re-read the paper). If you're using a drive which uses
technology X, you only need to perform the passes specific to X, and you
never need to perform all 35 passes. For any modern PRML/EPRML drive, a
passes of random scrubbing is the best you can do. As the paper says, "A
good scrubbing with random data will do about as well as can be expected".
This was true in 1996, and is still true now.
Looking at this from the other point of view, with the ever-increasing
density on disk platters and a corresponding reduction in feature size and
use of exotic techniques to record data on the medium, it's unlikely that
anything can be recovered from any recent drive except perhaps one or two
levels via basic error-cancelling techniques. In particular the the
in use at the time that this paper was originally written have mostly
out of use, so the methods that applied specifically to the older, lower-
density technology don't apply any more. Conversely, with modern high-
density drives, even if you've got 10KB of sensitive data on a drive and
can't erase it with 100% certainty, the chances of an adversary being able
to find the erased traces of that 10KB in 80GB of other erased traces are
close to zero.
- Re: Peter Gutmann data deletion theaory?, (continued)