Anonymity Control in Multi-bank E-Cash System

Most electronic cash systems in the literature have been developed in the single bank model in which clients and merchants have accounts at the same bank. In the real world, electronic cash may be issued by a large group of banks, monitored by the Central Bank. Thus not only client anonymity but also bank anonymity should be considered to simulate anonymity of real money. Because anonymity could be in conflict with law enforcement, anonymity of both clients and banks must be contollable such that the identity of the bank is concealed but identifiable by the Central Bank in case of dispute and the client is anonymous but revocable by a trusted third party. In this paper we study electronic cash system in the multiple bank model in which clients and merchants have their accounts at different banks, especially from the viewpoint of anonymity control. Client anonymity control and bank anonymity control are achieved by fair blind signatures and group signatures, respectively. By merging fair blind signatures and group signatures, we provide both client anonymity control and group anonymity control efficiently.