R: Wiping a drive: /dev/zero or /dev/urandom better?

["Vega - Brunello Ivan" <I.Brunello () vegaspa it>]

Although I don't trust too much on urandom, just for lack of (my) knowledge on its internals, I'd suggest using it 
instead of /dev/zero

I usually use a somehow circonvoluted method: create a truecrypt file as big as the partition (or, even better, 
truecrypt the whole partition).
For sure it writes random data, and such method works the same way in both linux and windows.
The only two concerns:
- AFAIK, it work on partitions, and not on whole disks.
- you have to use an external program (so you have to keep it around, etc), while "cat" or "dd" are almost always 
available.


Ivan Brunello

 
> -----Messaggio originale-----
> Da: listbounce () securityfocus com [mailto:listbounce () securityfocus com]
> Per conto di JW
> Inviato: martedì 14 ottobre 2008 0.47
> A: security-basics () securityfocus com
> Oggetto: Wiping a drive: /dev/zero or /dev/urandom better?
>
> I've got a theoretical question: when wiping a drive (I'm talking about
> Linux
> here), which of the following is more: fill the drive with data
> from /dev/zero or /dev/urandom?
>
> I ask because I often see people suggest something like the following
> for
> wiping disks:
>
> cat /dev/zero > /dev/hda
>
> (and of course do it multiple times)
>
> I got to thinking that (if you are really paranoid) it would probably
> be
> easier for "the bad guy" to recover original data if you use /dev/zero
> because it's so uniform, the "bad guy" can just look for anything other
> then
> zeros - if it's not zero, it's data.
>
> Which would imply that overwriting the data with /dev/urandom or
> /dev/random
> would be more secure.
>
> But I don't know enough about the internals of hard drives to know if
> it
> really matters or not.
>
> For clarity I'll point out that I'm not talking about wiping files in
> the
> filesystem, I'm talking about wiping whole disks - I guess you'd say
> "at the
> block level".
>
> What do the resident experts here think?
>
>       JW
>
> --
>
> ----------------------
> System Administrator - Cedar Creek Software
> http://www.cedarcreeksoftware.com