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Re: Gutmann's research paper today
From: Valdis.Kletnieks () vt edu
Date: Tue, 07 Feb 2006 10:07:38 -0500

On Tue, 07 Feb 2006 15:44:37 +0100, gimeshell () web de said:

Am i misunderstanding something or you can really say, if you're
writing to a modern disk, forget all special scrubbing technologies,
don't use Gutmann, don't use DoS 5220.22M or other pattern writing
technologies, only a few passes of random scrubbing will do the job?

DoD 5220.22M only requires 3 passes and verify of each pass - all zeros, all
ones, and all "the same character" (for instance, 'AAAAAAA..' or similar).
That's good for sanitizing disks up to Secret.  For anything higher, physical
destruction is mandated. A "few passes of random scrubbing" is probably
equivalent to 5220.22M for any realistic usage.

One place where "random scrubbing" falls down is the requirement to *verify*
that the blocks were written.  If you wrote a disk full of zeros, it's a
trivial matter to read it back and verify that all the bytes are zeros.  If you
wrote a whole disk of pseudo-random, then you have to regenerate the entire
pseudo-random data stream in order to compare it....

And yes, the verify step is important - I've had more than one disk drive that
was still perfectly readable, but suffered hardware damage to the write hardware.
Writing 3 passes of anything and failing to verify on such a disk would result
in a disclosure of the entire disk's contents.  Yes Virginia, there *are* disk
drive failures that will report a successful write but not actually work... ;)

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