A SMART CARD BASED OFF-LINE ELECTRONIC CASH PAYMENT SYSTEM WITH FAIR TRANSACTIONS

Secure and fair electronic payment mechanism has become more and more important due to the rapid growth of electronic commerce over the Internet. Scash is a smart card based off-line electronic cash payment system which has been proposed and patented by the Kent Ridge Digital Labs. In this thesis, we first present the original Scash system and analyze its security features. Based on the analysis, we present two advanced payment protocols which improve the original Scash system through guaranteeing fair exchange over open networks such as the Internet. Fairness in both protocols is achieved by making use of an off-line Trusted Third Party (TTP). The first protocol is designed from the point of view of after-transaction resolution. This protocol is more efficient than the second one and is best suited for transactions involving low value payments. The second protocol actively prevents any possible cheating by each party. This protocol provides better security than the first one but at the cost of a higher message overhead; therefore, it is most suitable for high value transactions. Our security analysis shows that both protocols meet the requirements for fair exchange over open networks. We also design a software system to implement and test, the protocols.

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• YAN ZHENG