How does the 'tamperproof' nature of the software help at all? It's still possible to double-spend in any off-line cash system by making multiple copies of the tamper-proof modules.. the only security provided is in obscuring the algorithm.
If multiple transactions involving the same instrument reveal the double-spender, then appropriate action may be taken. One could of course do the exact same transaction twice with the exact same person using identical copies of the tamperproof module, but that would yield no more data than having done the transaction only one time, and certainly wouldn't create any additional value.
Speaking of digital cash, many thanks to the author of the 'magic money' software. I am in the process of integrating it with a local bulletin board, which should hopefully be available on the net sometime this summer.
One nice application of Magic Money would be to purchase subscriptions and other services from a BBS. It is often highly inconvenient to have to mail in a payment, and if you are paying for something in another country, sending something that can be cashed overseas. Digital Cash would solve all these problems. -- Mike Duvos $ PGP 2.3a Public Key available $ mpd@netcom.com $ via Finger. $