Re: OT - Wipers

["JohnH" <pctech@htc.net>]

Doc (and everyone else)
Thank you for the information. It has been very helpful (especially Doc's 
description). I now know why the (BC Wipe) program also includes preset 
wipes at higher than 30 passes. The biggest problem is, with every pass the 
length of time grows and can take days. I know this because I tried the 
maximum preset once. And that was on a small 8GB HD. I now know the only 
TRULY safe HD is a Melted HD.




----- Original Message ----- 
From: "Robert G. (Doc) Savage" <dsavage@peaknet.net>
To: <silug-discuss@silug.org>
Sent: Thursday, August 25, 2005 9:01 PM
Subject: Re: OT - Wipers


> On Wed, 2005-08-24 at 23:55 -0500, JohnH wrote:
>> I have a Windows program called BC Wipe. It is suposed to wipe the files 
>> (or
>> HD) to government standards.
>> First could this statment true and second, is there a Linux type wiper?
>> Also, exactly how does a wiper work?
>
> At the physical level it's one thing to overwrite a "track" with new
> vanilla data. The important thing from a forensics standpoint is your
> definition of a track. In reality a r/w head is positioned by a servo
> which does a fairly good, but not necessarily perfect, job of writing
> the new data pattern over the old. Think of a tractor trying to plow
> exactly over an earlier furrow. There's a little variance to either side
> caused by temperature, gravity, phases of the moon, and good ol' karma.
>
> Flanking that r/w head are two small "trimmer" heads which write white
> noise on either side of the written track. Their job is to make it
> easier for the r/w head to detect good from bad during the next read
> path. Think of it as looking out onto a fairway and seeing it bound by a
> high grass rough on both sides.
>
> In real life, the trouble with this model is that data written by a r/w
> head tends to spill over into the rough on both sides. Those trimmer
> heads don't always remove everything that spills over to the left and
> right, especially when the centerline wanders due to temperature changes
> from one pass to the next.
>
> It is sometimes possible, using exotic sensor techniques like laser
> scattering, to read the vestigial remains that exist like leftovers
> beyond the snubber tracks. If the laser beams are focussed onto track
> centerlines rather than their shoulders, you can recover data from badly
> damaged disks like those from PCs found in the World Trade Center rubble
> that belonged to Cantor Fitzgerald.
>
> If only one re-write pass has been made over an existing "track",
> chances are fairly good that a substantial portion of the previous data
> can be read from the shoulder areas using laser scattering. The basic
> idea behind DoD 5220 "wiping" is to repeat the overwrite process enough
> times to reduce any vestiges of the original data to levels that cannot
> be detected by laser scattering.
>
> If, and only if, your "BC Wipe" utility is explicitly certified to be
> DoD 5220 compliant can it be used to reliably erase a disk containing
> classified national security information. Otherwise the only generally
> accepted wiping tool is a sledgehammer.
>
> --Doc
>
>
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