On 18/11/12 10:16, Tyler J. Wagner wrote:
On 2012-11-16 17:30, Alan Pope wrote:
More passes don't really give you any benefit. A simple single run of dd
is sufficient.
That depends against what you are trying to defend. It is possible, with
specialist tools, to recover data after a single wipe.
People say that a lot. Prove it.
This is especially
true when the wipe is done with uniform data, such as all zeros. So if you
want to prevent the next owner of a laptop from running photorec, one pass
is fine. If you want to stop a data recovery specialist or intelligence
agency, it is not.
A while back someone tested this theory which is well distributed by
technical people. He put a known string in a file on a disk, then dd'ed
zeores over it and called file recovery companies to challenge them to
get it back. As soon as he mentioned he'd done a single pass of dd'ing
zeroes over it _none_ of them would accept the challenge.
One professional data recovery company replied with:-
"According to our Unix team, there is less than a zero percent chance of
data recovery after that dd command. The drive itself has been
overwritten in a very fundamental manner. However, if for legal reasons
you need to demonstrate that an effort is being made to recover some or
all of the data, go ahead and send it in and we'll certainly make an
effort, but again, from what you've told us, our engineers are certain
that we cannot recover data from the drive. We'll email you a quote."
Cheers,
--
Alan Pope
Engineering Manager
Canonical - Product Strategy
+44 (0) 7973 620 164
alan.p...@canonical.com
http://ubuntu.com/
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