Research On Off-line Electronic Cash Protocols

As the progress of global information advanced rapidly, the studies and realizations of e-commerce via Internet have come to be hot spots for the academe and business all over the world. The security of e-commerce is one of the most important obstacles to hold back its development. How to realize a secure, efficient and facile payment via the insecure network has attracted more and more attention. Since electronic cash (e-cash) can be used to play the role of physical cash payment in real life, it will be an indispensable payment means in the electronic payment (e-payment) infrastructure of future global information society. Based on the project of national natural science fund of "Research on the secure payment protocol for e-commerce", this thesis has engaged in extensive research on some relevant theories, protocols, key technologies and actual implementation of e-cash.Through analyzing and comparing the main characteristics of e-payment based on credit card, e-check, e-cash and micropayment, the thesis demonstrates that e-cash is the most suitable means of e-payment for the present e-commerce via Internet. Besides, the thesis also summarizes the history, status quo, achievements of e-cash theory and the present progress of practical e-cash systems abroad.Restrictive blind signature is the essential technology in the implementation of efficient off-line e-cash system. As the extension of restrictive blind signature, partially restrictive blind signature allows some public information to be included in the signature while the anonymity and exposure ability against double signer of receiver are still hold. We propose an efficient partially restrictive blind signature protocol to modify the format of blind transforming for both receiver and signer. In contrast with the protocol provided by Maitland, not only the modular computation overhead and traffic in ours are reduced dramatically, but also the length of signature becomes even shorter, thus ours protocol is more suitable for constructing e-cash payment than Maitland's.In all of e-cash schemes already proposed, there exists a great drawback, i.e. the size of payment transcripts database of bank will expand without any bound. Hereafter, the concept of validity duration for e-cash is introduced in this thesis. Applying our partially restrictive blind signature protocol, the thesis proposes an efficient off-line e-cash system based on discrete logarithm and representation problem. In this system, not only the on-line transaction is increased, but also the e-cash with various denominations can be issued only by a single secret key for the bank. At the same time, the size of payment transcript database of bank can be controlled in a rational range. To cope with dishonest users' double spending beforehand and some criminals' perfect crimes, the system can be extended to e-cash system with smart card and anonymity revocation through little modification.Aiming at the distinguishing features of users' payment hardwares with poor computer power and memory in mobile payment system, the thesis also proposes a new off-line e-cash system based on ellipse curve. By making full use of its superiority of even shorter key under the same security requirement, the efficiency of users' operation in withdraw protocol is improved dramatically. The unforgeablity of e-cash in this system is also proved theoretically.The crucial chain for e-cash to be practical is how to realize an off-line e-cash system with divisibility so that the users are able to multi-pay their merchandise logically and accurately. To overcome the shortcomings of present divisible e-cash scheme, for the first time, the thesis introduces group signature into divisible e-cash system and view the e-cash withdrawn by users as the group certificate issued by group administrator. As all of ancestor nodes of the payment node are blindly transformed, the divided parts from one e-cash are no longer linkable. On the basis of signatures based on zero-knowledge proofs and strong RSA problem, the security...