Re: Do softupdates eliminate the effectiveness of secure delete programs?

[Chris Zakelj <c.zakelj@ieee.org>]

matt wrote:

>I started playing with secure delete programs such as srm, wipe, and shred 
>all which overwrite diskspace with 0's or random data a number of times 
>before unlinking the file.  This is from the GNU shred --help:
>
>-------------------------------------------------------------------------------
>
>CAUTION: Note that 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.  The following are examples of filesystems on which shred is
>not effective:
>
>* log-structured or journaled filesystems, such as those supplied with
>  AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
>
>* 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
>
>-------------------------------------------------------------------------------
>
>The question is how do softupdates affect the functionality of secure 
>delete programs.  If the file is only overwritten multiple times in the 
>disk cache or memory, but just once on the disk itself, then I would think 
>that using secure delete on softupdates partitions would be pointless.  
>But maybe I'm wrong or don't understand this correctly.
>
>				-Matt-
>
Recycling this from a FAQ addition submitted about a year and a half ago 
(not by me, but I can just hear a certain someone getting his soapbox 
ready now)...

***
The only guaranteed way to delete data is to physically destroy the
hard disc that contains it.  Theo likes to use the magnets to hold 
photographs to his fridge.  Others enjoy pyrotechnic displays when the 
platters are microwaved with a cup of water (this can be dangerous).  Do 
not try to bend or break the glass disc platters - tiny shards of glass 
can have unpleasant effects on human tissue when airborne.
 
Other attempts to securely delete data, such as overwriting with 
particular patterns a given number of times, do not guarantee that the 
data will not be recoverable later, given sufficient resources.  If you 
wish to use such methods, at your own risk, there are third-party 
utilities you can get.