Transfer protocols and complex payment transactions

We now briefly describe the transfer protocols between card- and software-based systems. Effectively, this is a composition of an online protocol between a user and a load/unload server, followed by an online protocol between the same user and the issuer of Section 2. Specifically, an account-based Unload protocol followed by a Coin Purchase protocol similar to that of Figure 5. The issuer acts as the payment agency in the Unload protocol. Call this combined protocol Cardcash-to-Softcash.

The reverse direction, software cash to card cash, is composed of the Redeem protocol between the user and issuer, followed by the Load protocol of Figure 8 between the same user and a load/unload server. Again, the issuer acts as the payment agency in of the Load protocol. Call this protocol Softcash-to-Cardcash.

In the same way, transactions between users from the same or different payment ``media'' are also enabled. For example, the payment from one card user to another is achieved as follows. This type of transfer can be accomplished by any intermediary, in particular, the issuer of Section 2:

1.

The payer runs Cardcash-to-Softcash;

2.

the payer, payee and issuer run the Payment with Redeem protocol (Section 3);

3.

the payee runs Softcash-to-Cardcash.

Note that in the card-based system a clearing system is used for transfering money back and forth between the load/unload servers and the payment agencies. Thus, there is not much of an overhead in running these composed protocols. At the end of the three steps above the payment agency (the issuer) and the load/unload server are even.

Similarly, card payers can pay software payees with not much of an overhead, since a clearing system is involved. Here, the unload server owes money to the issuer. In the reverse direction, the issuer owes money to the load server.