[H-GEN] dd or shred for secure delete - no html

[Anthony Irwin]

Hi,

Sorry yahoo changed my settings without asking me to
html it's back to text now hopefully.

I was under the impression that dd bs=1024
if=/dev/zero of=foo_file would securely delete a file
by adding /0 to every byte of the file and the dd
bs=1024 if=/dev/zero of=/dev/hda would securely delete
a hard drive.

I have however seen a web site that said that you
should use a tool like shred because the method i
mentioned above is not a secure way to delete files.
Reading the man page of shred also said:

----------------------------
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

In  addition, file system backups and remote mirrors
may contain copies
of the file that cannot be removed, and that will
allow a shredded file
to be recovered later.

------------------------------------

So I was wondering if anyone knows the difference
between the dd and shred methods of deleting files and
hard drives and what the best way is.

Kind Regards,
Anthony Irwin


	
		
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