1. How many different coins (serial numbers) can the current Mark Twain/Digicash protocol support? 2. Does Mark Twain bank maintain 2 lists: 1 of all the ecash serial numbers for all coins ever produced, and 1 of all the ecash serial numbers for all coins that have been spent before? Or just 1 list of the spent coins (assuming that any coin that is signed w/MT's private key and does not appear on the "spent" list is still valid and is not counterfeit)? 3. The Digicash scheme allows each coin to be used only once and then destroyed. How many coins will it take before all possible coins are minted, used and destroyed thereby requiring banks to issue new coins with "recycled" serial numbers? Remember, each time a "transaction" takes place, an existing coin is destroyed and a new coin is minted. and a transaction can simply be Alice giving her friend Bob a dollar (not necessarily using the ecash for a purchase) 4. What is the probability of guessing a valid serial number, assuming there are 1 million, 1 billion or 1 trillion coins in circulation? 5. Suppose you have a very large number of cash coins signed by the same bank (say, Mark Twain) and you know the record layout of each coin (easy enough since you can decrypt it with the bank's public key), and for each coin the "bank name" field is the same (because it's the same bank!) -- then, would it be possible to hack the RSA encryption and recreate the bank's private key? -----BEGIN PBP SIGNATURE----- Version: 1.0.0, Copyright 1995, Pretty Bad Privacy David Klur dklur@dttus.com I am who I am because I say so. So there. -----END PBP SIGNATURE-------