[olug] [OT] IBM Authorized service center in Lincoln...

[Jeff Hinrichs - DM&T]

Actually if you are concerned about someone reading via residual
magnetic levels, a variation on the gutmann method would be the way to
go.
http://en.wikipedia.org/wiki/Gutmann_method   -- drive electronics
have changed since then but the basic idea remains.

An analogy would be you want to obfuscate a phone number written by
pen on paper.  You can try and scribble over it, black it out with a
marker but you can still make out the numbers.  The only way to
effectively obfuscate the number without destroying the media is to
write the remaining nine numbers over each position with the same ink
as the original.  So if you want to obfuscate a 5, you would
successively write 6,7,8,9,0,1,2,3,4 over the 5 making it very hard to
determine what the original number actually was.  You repeat the
process to each digit you want to obfuscate.  Want to make it harder?
make another pass starting with 5.  The goal is to make all 10 digits
equally likely to be seen.

Gutmann is the same idea but applied to mfm/mll disks.  Writing all
0's once leaves the theoretical possibility of  equipment sufficiently
advanced to detect smaller residual differences and still be able to
make a good analysis of the disk.(some bits are not as 0 as others)
You need to remember that magnetic field levels are not digital, but
analog.


Paranoid me?  Who said that? :)

-Jeff
+1 for DBAN

On Sun, Nov 1, 2009 at 2:27 PM, Kevin D. Snodgrass
<kdsnodgrass at yahoo.com> wrote:
> --- On Sun, 11/1/09, Christopher Cashell <topher-olug at zyp.org> wrote:
>> From: Christopher Cashell <topher-olug at zyp.org>
>> Running:
>>
>> # dd if=/dev/zero of=/dev/sdX
>>
>> Will probably be a little more thorough. ;-)
>>
>> (Reading from /dev/null returns End Of File; reading from
>> /dev/zero
>> returns zeros.)
>
> DOH!!  Watching football and typing an email message can lead to /dev/random results!
>
>
> Kevin D. Snodgrass
>
>
>
>
>
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-- 
Jeff Hinrichs
Dundee Media & Technology, Inc
jeffh at dundeemt.com
402.218.1473
web: www.dundeemt.com
blog: inre.dundeemt.com