I once wondered if the colorful fibers in bank notes — which, like the nonpareil spheres, are distributed at random throughout the paper on which the notes a printed — can also be used to generate a unique number.
Examples (aha, including a teaser to an upcoming product called “Verifibre”!) can be seen here:
Instead of a lookup table, that number could be signed and the signature printed onto the bank note itself. It would be impractical to either deduce the signing key or duplicate the pattern of fibers in a way that the signature was still valid.
I don’t know if there’s a signature algorithm though that is resilient to lossy and unreliable input data and which can also produce short enough output that could be printed on the face of a bank note.
