thoughts on one time pads

leichter_jerrold at leichter_jerrold at
Sun Jan 29 18:42:24 EST 2006

[CD destruction] 
| You missed the old standby - the microwave oven.
| The disk remains physically intact (at least after the
| 5 seconds or so I've tried), but a great deal of pretty
| arcing occurs in the conductive data layer. Where the
| arcs travel, the data layer is vapourized. 
| The end result is an otherwise intact disk in which the
| data layer is broken up into small intact islands 
| surrounded by clear channels. It might be interesting
| to try a longer burn, in which case you might also
| want to put a glass of water in with the disk(s) to
| preserve the microwave's electronics.
| This is probably less effective than the other methods
| you've described, but its very fast and leaves no noxious
| residues. It also uses a very commonly available tool.
As always, who are you defending against?  There are commercial "CD
whose effect - preserved islands with some destroyed material - is produced
a much more prosaic approach:  The surface is covered with a grid of pits.
Only a small fraction of the surface is actually damaged, but no standard 
device will have any chance of reading the disk.  I suppose specialized 
hardware might do so, but even if it code, there's the question of the 
encoding format.  CD's are written with error-correcting codes which can 
recover from fairly significant damage - but if the damage exceeds their 
correction capability, they provide no information about what was there to 
begin with.

If you want to go further down the same route, grinding the whole surface of

the disk should work even better.

Of course, all this assumes that there's no way to polish or otherwise
the protective plastic.  Polishing should work if the scratches aren't too
deep.  (The pits produced by the CD shredder" I've seen look deep enough to 
make this difficult, but that's tough to do over the whole surface.)

Probably the best approach would be "better living through chemistry":  It 
should be possible to dissolve or otherwise degrade the plastic, leaving the

internal metallic surface - very thin and delicate - easy to destroy.  One 
would need to contact a chemist to determine the best way to do this.  (If
else fails, sulfuric acid is likely pretty effective - if not something you 
want to keep around.)

Realistically, especially given the error-correcting code issues, anything 
that breaks the CD into a large number of small pieces probably puts any 
recovery into the "national lab" range - if even they could do it.

							-- Jerry

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