i wrote-

...

[Physical signature] 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.

Allen J. Baum replied-

To keep black market forgery part off the market, a 30% tolerance is way more than enough. There should be no false negatives (making a real part look fake), but if 1/3 of the forgeries slip through (i.e. 2/3 don't), this has the affect of driving the forgery price up by a factor of 3, effectively pricing them out of the market.

I don't see how you factor out the variables of the resolution, what physical property is scanned, etc. For some combinations, it would be easy to forge 100% matches. For others, it would be hard to get a 30% match on the original object... Maybe the whole scheme could be improved by a trap-door function that has built-in error-tolerance. (By the way, if anybody knows about fuzzy hash functions, please write me; I'm curious for other reasons.)

(Unless the real goods are overpriced a factor of 3...:-)

Isn't Great Art overpriced by thousands of times, in terms of reproduction cost? Anyway, a 2/3 rejection rate would be tough. -fnerd quote me - - - - - - - - - - - - - - - We shall have to evolve Problem solvers galore As each problem they solve Creates ten problems more. --Piet Hein -----BEGIN PGP SIGNATURE----- Version: 2.3a aKxB8nktcBAeQHabQP/d7yhWgpGZBIoIqII8cY9nG55HYHgvt3niQCVAgUBLMs3K ui6XaCZmKH68fOWYYySKAzPkXyfYKnOlzsIjp2tPEot1Q5A3/n54PBKrUDN9tHVz 3Ch466q9EKUuDulTU6OLsilzmRvQJn0EJhzd4pht6hSnC1R3seYNhUYhoJViCcCG sRjLQs4iVVM= =9wqs -----END PGP SIGNATURE-----