Research On Micropayment Protocols

With the rapid development of network and information techniques, electronic commerce is immersed in our daily life. How to realize a secure, efficient and facile payment for electronic goods or low value transaction via the insecure network has attracted more and more attention. Researches on e-commerce via Internet have come to be hot spots for the academe and business all over the world, however, the security of e-commerce is one of the most important obstacles to hold back its development. As one of payment means for digital coins, micropayment is a new development direction of electronic payment which satisfies perfectly the transaction requirements of electronic goods or service. Compared with macropayment, each deal for micropayment is worth low value and efficiency is the preference when the system is relatively secure. Supported by the National Science Foundation of China, this thesis has engaged in extensive research on some relevant theories, protocols, key technologies and actual implementation of micropayment. In this thesis, we analyze the background, features and model of micropayment in detail, then select security and efficiency as our research goal based on the analysis and remark of status quo and problems remaining unsolved. All the micropayment systems fall into three categories, i.e. micropayment systems based on scrip, hash chain, probability according to the evolvement of micropayment. Scrip acts as one of the common means for micropayment. We introduce systematically the basic definition, creation methods, main characteristics, typical structure and verification methods of scrip, then gives three scrip payment protocols (scrip in the clear, encrypted network connection and request signatures) and analyze the related performance in brief. In this thesis, we propose a new efficient micropayment scheme, where a merchant can authorize the broker via licensed scrip production to create vendor scrip which the vendor validates and accepts on-line during payment. Moreover, all the information with regard to payment is encrypted using a shared symmetric key, which improves the security standard of our scheme and can prevent the consumer from double spending because the identifier of the scrip is unique. Compared with other micropayment schemes in existence, no public-key operation is required and the information stored is very simple, which minimizes the computation and storage overhead dramatically. So our scheme is efficient, secure and supports divisibility and transferability of digital coins in a simpler way. Hash chains are used widely in micropayment since they have many virtues such as high efficiency and security. We points out that there exist some problems in PayWord such as public key signature and possible attacks, and propose a micropayment scheme based on Merkle tree in which hash chains are designed to be spent at many merchants, while digital coins in PayWord can only be used for payment at a single merchant. We reduces the number of signatures required by allowing multiple hash chains to be signed with a single signature which can be done by linking the chains together through Merkle tree. We also present an efficient micropayment scheme based on multi-hash chains to solve the divisibility of digital coins in PayWord. Finally, we propose a new fair micropayment scheme, which is an off-line, prepaid scheme and supports divisibility of digital coins in a simpler way. Moreover, in our scheme, a hash chain can be used to have transactions with different merchants and an iterative payment protocol is performed which protects the profits of both consumers and merchants to improve the fairness of our scheme. The efficiency of micropayment system can be improved dramatically by introducing the mechanism of probability, which means the broker need only to tackle those deals according with the probability conditions, or the broker calculates the probability constants to decide whether he verifies the customer's payment information on-line. We presents a micro electronic lottery payment scheme, which are applicable in the scenario where electronic lotteries are used for payment frequently for it is efficient and supports divisibility of digital coins. Moreover, we propose a new micropayment scheme based on PayWord, where possible overspending is radically reduced by the adoption of probabilistic polling in a transaction. On the other hand, the losses caused by a dishonest overspending consumer must be shared by brokers and merchants. Furthermore, an iterative interactive payment protocol is performed which protects the profits of both consumers and merchants. Based on the basic theory of micropayment schemes, a prototype system is designed and developed. The thesis establishes the system model and overall framework, describes the definition and functions of related modules, gives the information flow of micropayment deal and presents some techniques and theories with respect to the test and certification of micropayment system. This prototypesystem realizes the core functions of micropayment system and establishes a solid foundation for developing of micropayment product. In conclusion, we propose the further development directions of micropayment system.