CD shredders, was Re: thoughts on one time pads

[Jack Lloyd]

On Wed, Feb 01, 2006 at 05:50:24AM -0600, Travis H. wrote:
> On 1/28/06, dan at geer.org <dan at geer.org> wrote:
> > In our office, we have a shredder that happily
> > takes CDs and is designed to do so.  It is noisy
> > and cost >$500.
> 
> Here's one for $40, although it doesn't appear to "shred" them so much
> as make them pitted:
> 
> http://www.thinkgeek.com/gadgets/security/6d7f/

If you packaged up your OTP material into blocks using an all-or-nothing
transform you could probably be certain that this would suffice, as long as the
blocks you used were large enough that it was at least statistically probable
that 'enough' bits of each block were destroyed or made unreadable. I believe
specifically you'd want to make sure that 2^n is an infeasible amount of work,
where n is the minimum number of bits that will be lost from any block by the
destruction process. This seems to generalize nicely, for example if an entire
CDs worth of material was processed as a single block under an all-or-nothing
transform, just snapping the disk in half might suffice to prevent any
(computationally feasible) data recovery [though it would be quite annoying in
practice, since you'd have to process the entire disk to read even a single bit
from it]

-Jack

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