Dynamic Fair Electronic Cash Model without Trustees

A new fair electronic cash system is proposed based on group blind signature and secret sharing scheme. Our proposed system is dynamic: we propose a method to delete the dishonest banks that maybe attack the system, which was not mentioned in the previous literatures. Our proposed scheme does not need a trusted third party to trace users: a shop owning suspicious ecoin and the bank having issued the coin can collaborate to find the user using secret sharing scheme, however, any one of them can’t trace the user alone. Furthermore, a novel e-coin tracing method is used to prevent criminal activities: under normal situation, the bank issues ordinary e-coin, while under abnormal situation such as blackmailing, kidnapping etc., the bank issues marked e-coin, and at the step of deposit, any bank in the group can recognize the marked e-coin. Also, our scheme is constructed for multiple banks as in the real life, thus it is more practical.