How many overwrites for secure erase?

On another list, someone asked a question which piqued my
curiosity.

U.S. DoD requires 7 overwrites. The OP wanted a '*technical*
justification of "15-times" or any other number. Technical one,
not "because mama said so".'

Has anyone actually recovered data that's been overwritten
even once by random data? Twice?

We know about the theoretical techniques to get the data. We
know it would be horrendously expensive. But has anyone
*actually* done it?

And, regardless, is there some number of overwrites that
*will* make the data unrecoverable? The OP was looking for
something better than pulling a number out of the air (or
wherever) - a number with some theoretical or experimental
justification.

I figured if anyone had the answers (and was allowed to give
them), it would likely be someone in this group.

--
Arthur T. - ar23hur "at" intergate "dot" com
Looking for a z/OS (IBM mainframe) systems programmer position
.

Relevant Pages

  • Re: How many overwrites for secure erase?
    ... U.S. DoD requires 7 overwrites. ... justification of "15-times" or any other number. ... over-write many times with patterns and random data, ... platters out and physically destroy them. ...
    (alt.computer.security)
  • Re: Putting the "NSA Data Overwrite Standard" Legend to Death...
    ... still be exploited after multiple overwrites in a suitable lab environment ... > I was surprised, however, to learn that a "NSA standard" DOES NOT exist. ... in its assigned role within DoD. ...
    (Bugtraq)
  • RE: [Full-Disclosure] Erasing a hard disk easily
    ... WipeDrive3 is a DOD approved product that I use and it calls ... DOD-level wiping 3 passes with 3 overwrites each. ... random character and verify. ... METHOD IS NOT APPROVED FOR SANITIZING MEDIA THAT CONTAINS TOP SECRET ...
    (Full-Disclosure)