Securely delete files...

[David Shaw]

On Aug 20, 2008, at 4:08 AM, Werner Koch wrote:

> On Wed, 20 Aug 2008 02:32, dshaw at jabberwocky.com said:
>
>> However, as you are asking this question of the GnuPG list, I suspect
>> you mean to ask about GnuPG.  GnuPG does not have a secure delete
>> feature.
>
> Let me add that one reason for not providing a secure deletetion  
> feature
> is that gpg is Unix tool and as such it is usually operated in a
> pipeline and does not work directly with files.
>
> Most Unix systems these days have secure deletion tools like  
> shred(1) or
> wipe(1).  However, I doubt that they are any effective when used with
> modern disks.

There is some debate on whether a well-funded adversary can recover a  
useful amount of data (say enough to reconstruct a fragment of a file)  
from a disk that has been overwritten multiple times.  It's an  
interesting debate, but for many situations the question is somewhat  
moot.  Hard drive prices are so low these days that if the drive  
contains sensitive material that should not be exposed "no matter  
what", just destroy the drive.  If you're designing a system that  
requires that level of security, then the price of a new hard drive  
now and then is included.

For what it's worth, the US government recently changed their  
regulations on what qualifies for "clearing" (basically removal that  
can foil an undelete function or games with 'dd' and 'grep') and  
"sanitizing" (removal that can foil a laboratory).  The notable  
difference is that in the new regulations, you cannot use any  
overwrite method to sanitize a disk.  The only way to sanitize is to  
degauss the drive or physically destroy the thing.

David