RE: Interesting One

["Nero, Nick" <Nick.Nero () disney com>]

I was wrong on my original post.  I forgot to mention that you should
zero fill the drive THREE times to meet the NSA standard.  A buddy of
mine who has done some highly classified work says they had to write a
"random pattern of bits three times" to the media.  Other media (hard
drives, tapes . .. .) were destroyed.  My employer also simply destroys
the media.  

It is generally considered that after 3 times of being overwritten (the
previous respondant was correct that the OS only deletes the pointer to
the data when it "deletes" the file), the data is unrecoverable.  Simply
overwriting it once will do the trick for most cases, but the NSA
standards are designed for instances where the "other side" has lots of
resources (other governments).  Keep in mind that the goal of security
is to figure out if your measures are truly cost effective.  I am not
gonna zero fill my drive 3 times.  If someone is willing to deploy an
electron scanning microscope to see my "fascinating" .pst file, I will
just burn it to a CD and send the darn thing to them.

-----Original Message-----
From: Dozal, Tim [mailto:tdozal () cisco com] 
Sent: Tuesday, October 29, 2002 1:44 PM
To: Dave Adams
Cc: security-basics () security-focus com
Subject: RE: Interesting One


The NSA are the masters of these techniques, and what your hearing can
absolutely be done by the right tools and the right people.  There are
however ways to prevent the data from being recovered.  Some tools can
be used to sequentially set every sector on the HD to a binary 1 there
by erasing any of the patterns that these groups tools use to
re-construct previous data.  Aside from a sector by sector wipe of the
drive I don't think there is much you can do to stop somebody from
accessing even files you think were erased.

Basically in a nut shell when you erase a file from your drive all you
do is erase the pointer to the location where the file was kept, you
don't actually erase the files until new data is added to the drive and
the space allocated over writes the space where the previous file was.
So you could go onto your machine and delete every file on the system
but their not gone, the OS just can no longer see or reference their
locations.  The most basic of tools that these groups have will
sequentially walk through a drive and re-create the pointers to the
files, making them accessible again.

I'm sure a google search can come up with more information or actual
articles with names of the various tools available.  Hope that helps.

-Tim

-----Original Message-----
From: Dave Adams [mailto:dadams () johncrowley co uk] 
Sent: Monday, October 28, 2002 2:06 PM
To: security-basics () security-focus com
Subject: Interesting One


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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