Transferable Optimal-size Fair E-cash with Optimal Anonymity

Transferable electronic cash (e-cash) allows the recipient of a coin in a transaction to transfer it in a later payment transaction to the third person. The transferability is a desirable property in many applications. However, in the existing transferable e-cash, the size of coins is constant at the cost of increasing the users´ burden and not satisfying the optimal anonymity. On the other hand, the e-cash protocol with optimal anonymity has the drawback that the size of coins grows linearly in the number of transfers. In this paper, a transferable optimal-size e-cash is proposed using a different structure, that is, coins are divided into two parts. The new scheme achieves the optimal anonymity, i.e., it satisfies Observe-then-Receive Full Anonymity (OtR-FA), Spend-then-Observe Full Anonymity (StO-FA) and Spend-then-Receive Full Anonymity (StR-FA). Meanwhile, the users has not to keep in memory the data associated to all past transactions. At last, the security proof of the new scheme is given in the standard model.