Payments between individuals are carried out by inserting the card into a pocket sized electronic wallet and making 6 key strokes. Customers and retailers can deposit money into thier bank accounts over the phone.
If A can transfer to B offline, and B can transfer to C without calling into the bank first, this has to be either security- through-obscurity or non-anonymous at some level. You could stack digital signatures to represent a transfer chain. But you can't pass anonymous digicash from one person to the other without the possibility of double spending. Unless of course the recipient is required to dial in before using the received cash, in which case it isn't offline. If this system is truly offline (i.e. not cryptographicall secured), somebody is going to figure out how to rip it off.
However, cards could be locked to prevent unauthorised use by tapping in a four digit personal code. Once locked, the money could not be spent without
>reentering the code.
At least you don't have to worry about a brute-force search ;-)