RE: Peter Gutmann data deletion theaory?

From: dave kleiman (dave_at_isecureu.com)
Date: 07/24/05

  • Next message: Volker Kuhlmann: "Re: [BugTraq] Peter Gutmann data deletion theaory?" 
    To: <focus-ms@securityfocus.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.

    --------------Snip-------------------------
    >I'd love to hear some thoughts on this from security and data experts
    >out there.

    People should note the epilogue to the paper:

      Epilogue

      In the time since this paper was published, some people have treated the
    35-
      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
    than
      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
    encoding
      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
    few
      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
    data
      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
    drives
      in use at the time that this paper was originally written have mostly
    fallen
      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.

    Peter.

    --------------Snip-------------------------

    Dave Kleiman

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