[plug] HDD Erasure

[bob]

On Sun, 13 Nov 2005 09:46, Aaron Wooten wrote:
> Hi Chris, you may want to have a read of "Secure Deletion of Data from
> Magnetic and Solid-State Memory" By Peter Gutmann
>
> It is located at
> http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html

Shred, a program built on the principles of the above has some important 
caveats. Its readme says in part...
=====
shred relies on a very important assumption: that the
filesystem overwrites data in place. This is the traditional way to do
things, but many modern filesystem designs do not satisfy this assumption.
Exceptions include: 
* Log-structured or journaled filesystems, such as those supplied with
AIX and Solaris. 
* Filesystems that write redundant data and carry on even if some
writes fail, such as RAID-based filesystems. 
* Filesystems that make snapshots, such as Network Appliance's NFS
server. 
* Filesystems that cache in temporary locations, such as NFS version 3
clients. 
* Compressed filesystems. 
If you are not sure how your filesystem operates, then you should assume
that it does not overwrite data in place, which means that shred cannot
reliably operate on regular files in your filesystem. 
Generally speaking, it is more reliable to shred a device than a file, since
this bypasses the problem of filesystem design mentioned above. However,
even shredding devices is not always completely reliable. For example, most
disks map out bad sectors invisibly to the application; if the bad sectors
contain sensitive data, shred won't be able to destroy it. 
=====

IE, shred devices not files and don't expect there to be no data "trapped" 
in bad blocks left on the disk.

It comes down to who you are trying to protect yourself from. If its 
J.Random.Hackker then ordinary secure delete tools like shred and autoclave 
will be useful but if its a government agency... well how keen are they to 
find out what you're hiding? (even ordinary physical destruction may not be 
sufficient here for a significantly motivated organisation... got access to 
a blast furnace? :)

HTH.

> Hope this helps
>
> Aaron

-- 
The verdict of a jury is the a priori opinion of that juror who smokes
the worst cigars.
  -- H. L. Mencken