Digitally Signing Physical Objects

[FutureNerd Steve Witham]

> 3. The shop or customer wishing to authenticate the part takes the
> number stamped on the part, runs it through the *public* key of the
> manufacturer (widely available, not kept secret, of course) and gets
> back the feature vector, which he can then compare to what he actually
> sees on the object.
> 
> (This clearly requires similar hardware to what was originally used by
> the manufacturer. And some tolerance for variations in intensity
> caused by equipment variations, wear, new scratches, etc., is needed.
...
> 4. A would-be forger cannot generate a "digital object signature" that
> correctly decrypts through the published public key. 
> --Tim May

This seems to have a tricky dependence on the tolerance.  The forger can
get a valid plaintext and signed feature vector.  So, if the tolerance 
for error is too low, you get false positives, but if it's too high, a 
forger could create something starting from the feature vector.  An
interesting CAD/CAM problem.

-fnerd
quote me

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Problem solvers galore
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Creates ten problems more. --Piet Hein
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