Secure Erasing is actually harder than that...

Ray Dillinger bear at sonic.net
Mon Feb 19 11:38:13 PST 2001



A much better article on the topic can be found at 

http://www.cs.auckland.ac.nz/~pgut001/secure_del.html

The problem is that data that's been written over once, or even 
twice or ten times, can often still be read if someone actually 
takes the platters out and uses electromagnetic microscopy on 
them. 

If you "erase" data using the perl script in the article Jim 
pointed at, it will be safe from J. Random who doesn't have 
much time, money, or technique to spend on it.  But it won't 
be safe from TLA's, commercial data-recovery shops, or any 
seriously "hardcore" hackers (or people who, for example, know 
enough to take it to a commercial data-recovery shop). 

To actually finish the job, you'd want extremely low-level 
access to the drive, including the ability to micro-adjust 
the head alignment so as to write garbage both hubward and 
rimward of where the track you're trying to erase *ought* 
to be within its sector, which of course would require you 
to be able to relocate the info on the sectors physically 
hubward or rimward of the track you were trying to erase, 
because writing hubward or rimward with micro-adjustments 
within a sector could cause errors on those adjacent sectors. 

I don't know of any OS that provides sufficiently low-level 
HD access to allow people to create a portable utility that 
does really secure deletion.  Hell, a lot of Hard Drives 
don't even have drivers that support the needed operations.

The moral of the story is, in a really secure system, the 
plaintext NEVER hits your hard drive.  

				Bear


On Mon, 19 Feb 2001, Jim Choate wrote:

>http://linuxtoday.com/news_story.php3?ltsn=2001-02-18-016-20-PS-HW-HL
>-- 
>   The Laws of Serendipity:
>
>   1. In order to discover anything, you must be looking
>      for something.
>
>   2. If you wish to make an improved product, you must
>      first be engaged in making an inferior one.  
>
>   Tivoli Certification Group, OSCT
>   James Choate                           jchoate at tivoli.com
>   Senior Engineer                        512-436-1062
>





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