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 - - - - - - - - - - - - - - - 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-----