Ray Dillinger <bear@sonic.net> writes:
Bell handwaved on the point of obtaining digital cash for paying the assassin with. Bob the broker can go to the bank and obtain it in the usual way, of course - but then has to transfer it to Alice the assassin, and there's a sticky point involved. If he just "copies" the money to Alice, she can double-spend with impunity and it's Bob's identity that will be revealed.
You're assuming an offline cash system with embedded identity. It is more likely that initial digital cash implementations will be online. By the time such systems come into widespread use (if ever) wireless connectivity will be ubiquitous. Offline cash really can't compete. Attempting to trace, identify, catch and punish double spenders will be overwhelmingly more expensive than simply checking directly that the cash hasn't been spent before.
Conversely, if she provides tokens for the bank to sign, then Bob has a major problem getting them past the cut-and- choose protocol at the bank. Even if she provides enough tokens to completely populate the cut-and-choose protocol, those tokens still have to have splits of valid identification information for somebody in them - and giving them all to Bob so that Bob could complete the protocol with the bank - would imply that Bob is privy to that information.
There are far more efficient offline systems than cut and choose. You need to get past the A's and into the B's and C's in your protocol list. Check more recent work from Brands and Chaum.