With The Observer And Practical Electronic Cash System

A practical electronic cash system is firstly presented with the introduction of observers and the trustee. ESIGN digital signature and extended ESIGN subliminal channel are used to construct the protocol of electronic cash system. The observers make the double-spending forbidden. The bank which issues the electronic cash does not carry out the check-up of double-spending. Therefore, The bank does not keep any information about electronic cash except for a pair of its own secret keys. Hence, the system is more simple and practical. The trustee restricts the subliminal information between the bank and observers, thus preventing the possible leak of user's privacy. The trustee connects with the bank only during the protocol of withdrawing and depositing. Therefore, this system still is an offline electronic cash system. The introduction of observers and the trustee is not only reasonable but also making the new system more efficient and practical than any known electronic cash system. On the assumption that the data of the observers can not be tampered, the security of this system relies on the difficultyof factoring.