Fair Electronic Cash Based on Double Signatures

摘要

In order to decrease crimes such as money laundering, blackmailing etc. in electronic cash systems, fair electronic cash has been a major focus of academic research in electronic commence. When a bank finds some dubious cash or owner, the trusted entity or trustee can help him to revoke the anonymity of the cash. In the previous protocols, the trustee knows all the information of the cash whether he is trusted or not, that is, he can trace the user or cash unconditionally. Furthermore, the dishonest trustee may deceive a user, which means that he may withdraw cash while tracing other users. Such cases are unfair to the honest users. A new fair electronic cash protocol based on untrustworthy trustees is proposed in this paper. The key idea is that the coin structure should include the signatures of both the trustee and the bank so that the trustee shares the information of the cash with the bank, while we do not use the secret sharing scheme. In contrast with the previous protocols, neither the trustee nor the bank can trace the money without the help of the other entity. In this way, the privacy of the user is protected furthest. Also, the trustee is off-line in the protocol, which means that he will not be involved in withdrawing the cash. Therefore, the protocol is efficient for implement at ion.