On Tuesday, March 5, 2002, at 03:32 PM, Sampo Syreeni wrote: > A while ago I thought about how one might apply public key signatures to > physical currency. It came to me that if there was a way to generate > measurable properties in the notes which couldn't easily be reproduced > (essentially, physical randomness in the notes' composure), it'd be > possible to make counterfeit notes detectable by signing a hash of a > measurement of such randomness by a well known public key and barcoding > it > on the bill: if one possessed the key, one could produce arbitrary > looking > bills and just sign the hash. If one didn't have the key, and couldn't > cheaply enough reproduce whatever gave rise to the measurement, one > couldn't reproduce a valid-looking note. The randomness could come from > things like turbulent deposition of magnetic/fluorescent materials on > the > bill, something one might assume to be fairly expensive to reproduce > exactly. > > Is there some "prior art" to be found, anywhere? Does the idea sound > reasonable? (I tend to be of the opinion that paper money is here to > stay > for quite a while, and improving on the state of the art of > anti-counterfeit measures seems like a fairly good idea. Over that > background, Chaumian cash and the like do not make a lot of a > difference.) >
Yes, I wrote about this about a decade ago. "Light Signatures" was an LA-based company proposing to authenticate physical objects by taking a scan of some property (e.g., a scan of the striations in a factory-made Harley-Davidson motorcycle part) and then computing an RSA signature of this scan and printing it on the object. A customer (or a machine shop installing a part) could take the printed number, run it through the public key of the vendor, and produce an analog scan which they could compare to the analog scan they saw on the part. Anybody can take the number and verify that it matches the analog scan, but nobody except the private key holder can take the analog scan and generate a number which works as above. I was told about this company in 1989 by Jim Omura, then CEO of Cylink. I have no idea what became of the patents and the company. --Tim May "Aren't cats Libertarian? They just want to be left alone. I think our dog is a Democrat, as he is always looking for a handout" --Unknown Usenet Poster
