The Multi-bank May Revoke The Anonymity Of The Divisible E-cash System

E-commerce system is now developing at an enormous speed, whose final objective is to electrize every phase of commercial activity. Electronic payment system is the kernel of E-commerce system. Although the electronic payment system based on E-cash is still under developing, it might be widely used because of its advantage.The dissertation first gives an overview of the electronic payment system and the situation for E-cash. Then it analyzes the influence brought by using E-cash. In order to prevent crime and ensure the stability of macroeconomic, a good E-cash system should be a multi-bank and anonymity-revocable e-cash system controlled by the Central Bank.The divisibility of E-commerce is used to address the traditional problem of change in a trade, that is, to break up a big note into parts to accomplish payment. Because a divisible e-cash system allows the customer to use one e-cash to do multiple legal accurate payments and reduces the times of withdrawal, it can reduce the load of the network and improve the system efficiency. Therefore, a good e-cash system should be a divisible e-cash system.This dissertation proposes a multi-bank, anonymity-revocable e-cash system by using restrictive blind group signature technology. In this system the Central Bank is the group-manager and banks, issuing e-cash, are group members. E-cash can be validated by a unique group public key. Trusted third party is introduced into this system to make it capable of tracing e-cash and the withdrawer.Currently the divisible e-cash system uses binary tree algorithm or (N, K) payment algorithm. There are some problems such as complicated algorithm, more transmitting data, lower efficiency, etc. Because the duplicate payment checkup of divisible e-cash system has to be done in bank, this dissertation proposes that the e-cash contains the e-cash value and the payment protocol directly contains theinformation of payment value. The sum of payments of each e-cash is stored in the Central Bank Authorization Center for overspent checkup. If it is overspent, the credible third-part should be asked to identify the person who is overspent. Thus, a simple, practical and efficient divisible e-cash system is constructed.Because large amount of data is assembled and need to be handled in bank, the efficiency of the algorithm in bank will directly affect the cost of construction and operation of the e-bank system. Thus the efficiency of the algorithm in bank is very important. The dissertation is the first to introduce Central Bank Authorization Center and use probabilistic audit to improve the transation efficiency in bank. Besides, this dissertation has considered every phase of an e-cash system in constructing a practical e-cash system.