Electronic Cash Payment System

The researches on fair off-line electronic cash (FOLC) system have been one of the hottest topics on electronic payment system. This dissertation analyzes the flaw of existing FOLC systems, and proposes several new FOLC systems as follows:1. Forward-secure FOLC system with multi-bank and key-insulated FOLC system are proposed. In these systems, the bank's public key remains same, but the corresponding private key evolves with time, which improves the security of the bank's private key and decreases effectively the loss caused by exposure of the private key.2. An efficient FOLC system is proposed with partially blind signature. Denomination and period of validity are embedded into electronic cash, which simplifies the bank's administration and improves efficiency of double-spender checking.3. A FOLC system with compact cash is proposed. Based on strong RSA assumption and y-DDHI assumption, user can withdraw wallet with 2~k coins (where k can be negotiated by the bank and user), which reduces effectively the traffic between the bank and user and decreases the user's storage size.4. A divisible FOLC system is proposed based on strong RSA assumption and y-DDHI assumption. In this system, the binary tree approach is not adopted, all protocols are conducted in the order of O(1) and the coin can be divided discretionarily.