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Re: Interesting One
From: Greg van der Gaast <greg.van.der.gaast () ordina nl>
Date: Fri, 01 Nov 2002 14:11:48 +0100

This is exactly what I meant. The magnetic trace elements that are left off to the sides of the track can contain data from a write to that location that has since been overwritten, multiple times. This trace information even layers, to some degree, making it possible to actually see what was on the same specific area of the drive at different times. Much like layers of sedimentory rock.

There are limits to this as you can only have a fixed X number of layers with a fixed amount Y of magnetic material. I hope it's obvious to everyone here that any material off to the side of the tracks isn't going to be recoverable by any software method as the read thereof is beyond the hardware of the drive.

Regards,

Greg van der Gaast

Where do you want to hit your account manager today? (tm)


Chet Uber wrote:

Fact: You cannot read the drive if it is overwritten without being able to manipulate the path of the drive head. I do not mean deleting a file in DOS,
I mean overwriting the drive with dd for example. What they are talking
about is that the edges of the tracks have data still, and you can
disassemble the drive and use force microscopy to read what is left. This is
a well known issue.

The overwritten by X times is irrelevant if you are trying to recover using
software. You cannot recover these drives.

http://www.c3i.osd.mil/org/cio/doc/computerdisposal.doc .


Chet Uber





----- Original Message -----
From: "Greg van der Gaast" <greg.van.der.gaast () ordina nl>
To: <security-basics () securityfocus com>
Sent: Wednesday, October 30, 2002 4:53 AM
Subject: RE: Interesting One


Last I heard from some DoD/NIPC people (and this was well over a year
ago) is that they were able to successfully retrieve at least partial
information off a disk that had been overwritten 153 times. Assume that
(at least government) forensic techniques have improved since.

Hope this helps!

Regards,

Greg van der Gaast
Ordina Public SDS West
Security Services

-----Oorspronkelijk bericht-----
Van: Carol Stone [mailto:carol () carolstone com]
Verzonden: Tuesday, October 29, 2002 9:58 PM
Aan: security-basics () securityfocus com
Onderwerp: Re: Interesting One

I don't know much about this, but yesterday I read in one of the later
chapters of Bruce Schneier's book, "Secrets and Lies," (link to amazon
follows) that over-writing data on a disk does *not* completely
obliterate it, it just makes it a lot more difficult to recover with
each over-write. I believe he said just how many re-writes were still
recoverable was a secret one of our governmental organizations wasn't
about to give up.  I'll look at my book later when I have it in my
hands and see if I can't find part and post a pointer to *his*
reference.

-carol

http://www.amazon.com/exec/obidos/tg/detail/ -
/0471253111/qid=1035924654/sr=8-3/ref=sr_8_3/104-4454644-5987143?
v=glance&n=507846

Greetings Folks,

I had an interesting conversation today with someone from FAST
(Federation
Against Software Theft) They pretend not to be a snitch wing of the

BSA.

Anyway, to get to the point, the guy that came to see me said that

their

forensics guys could read data off a hard drive that had been written
over
up to thirty times. I find this very hard to believe and told him I
thought
he was mistaken but the guy was adamant that it could be done. My
question
is, does anyone have any views on this, or, can anyone point me to a
source
of information where I can get the facts on exactly how much data can

be

retrieved off a hard drive and under what conditions etc etc.

Thanks

Dave Adams



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