Informatica

In 1995, Wu proposed a remote login authentication scheme based on geometric approach. However, Chien, Jan and Tseng presented a cryptanalysis of Wu’s scheme to show that it is not secure. Moreover, they proposed a modified version of Wu’s scheme. This paper presents there is a serious weakness in this modified remote login authentication scheme. We show that an illegal user can easily forge a valid login request in the modified version proposed previously.

Many electronic cash systems have been proposed with the proliferation of the Internet and the activation of electronic commerce. E-cash enables the exchange of digital coins with value assured by the bank's signature and with concealed user identity. In an electronic cash system, a user can withdraw coins from the bank and then spends each coin anonymously and unlinkably. In this paper, we design an efficient anonymous mobile payment system based on bilinear pairings, in which the anonymity of coins is revocable by a trustee in case of dispute. The message transfer from the customer to the merchant occurs only once during the payment protocol. Also, the amount of communication between customer and merchant is about 800 bits. Therefore, our mobile payment system can be used in the wireless networks with the limited bandwidth. The security of the new system is under the computational Diffie–Hellman problem in the random oracle model.

Smart card has been adopted to various applications. In 2000, Hwang and Li proposed a remote user authentication scheme, which is also using smart card. Nine months later, Chan and Cheng pointed out that there is a weakness in the remote authentication scheme proposed by Hwang and Li. In this paper, we show that Chan and Cheng's attack does not work well because they did not consider the format of user's identity. In addition, we propose several ways to solve the problem of Chan and Cheng's attack.

This paper discusses a known-plaintext attack on a redundancy reducing cipher method which is proposed by Wayner. We also propose an extension of Wayner's redundancy reducing cipher scheme so that the security will be improved greatly.

Recently, Harn proposed an efficient scheme that can batch verification multiple RSA digital signatures. His scheme can reduce signature verification time. However, there is a weakness in his scheme. In this study, we present two methods to against his scheme.