> Not really. Illuminating the device at different locations and > angles is certainly not as good as a cryptographical challenge. > Since the location and angle is done by some mechanical device, > the numers of locations and angles is certainly "small"
I think you're right here; in order for the challenges to be reproducable, the locations / angles that the reader uses would have to be discrete, probably by some sort of stepper motor. However, if the readers are autonomous (and each one needs to see the physical token once in order to identify it later,) then every reader could be calibrated differently, and would therefore use one relatively small subset of locations / angles out of a large number of subsets. > and once you are in posession of the token (e.g. as a clerk ini > the shop), it might be possible to generate a complete table of > all location/angle/response triples. I wonder if an analysis of the diffraction patterns produced by passing light though a token like this would provide enough information to reconstruct the internal 3-D shape... it strikes me as being a problem similar to X-ray crystallography. Ian Clelland <[EMAIL PROTECTED]> --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]