[vox-tech] Most efficient way to wipe hard drives

[Chanoch (Ken) Bloom]

On Thu, Sep 10, 2009 at 09:56:54AM -0700, Brian Lavender wrote:
> On Wed, Sep 09, 2009 at 09:20:30PM -0700, Bill Broadley wrote:
> > 
> > Short answer, one wipe is enough (At least for NIST, and one of the British
> > Infosec standards), wipes miss bad sectors, the ATA secure erase command is
> > worth checking out.
> [snip]
> I think caching is a concern on some systems, so more wipes seems to
> magically make the write go to the actual media. But I would agree with
> one wipe is probably enough. I had not thought about bad blocks. 
> 
> > 
> > So if you don't use secure wipe and won't lose sleep at night over a few bad
> > blocks being potentially recovered I'd recommend something like:
> > 
> > dd if=/dev/urandom of=/dev/sd<whichever disk>
> 
> Your computer must have a lot of entropy! Note that that device gathers
> entropy from the system. When an event happens, it may be worth one or
> two bits. Last time I wrote a program that read from that device, it
> seemed that I got a number of bytes, and then I had to wait as various
> events occured to the system. That is why they often tell you to move the
> mouse around when generating keys. It generates entropy for the system.

/dev/random, blocks waiting for entropy.
/dev/urandom doesn't wait for entropy. It uses entropy if it's
avalable, and switches to a PRNG if there isn't enough entropy. I
think it's similar to what you suggest doing with AES.

--Ken

-- 
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/