Cryptanalysis and improvement on two efficient remote user authentication scheme using smart cards

In 2002, Chien et al. proposed an efficient remote authentication scheme using smart cards, in which only few hashing operations are required. Later, Ku et al. gave an improved scheme to repair the security pitfalls found in Chien et al.'s scheme. Also Yoon et al. presented an enhancement on Ku et al.'s scheme. In this paper, we show that both Ku et al.'s scheme and Yoon et al.'s scheme are still vulnerable to the guessing attack, forgery attack and denial of service (DoS) attack. In addition, their schemes lack efficiency when users input wrong passwords. To remedy these flaws, this paper proposes an efficient improvement over Ku et al.'s and Yoon et al.'s schemes with more security. The computation cost, security, and efficiency of the improved scheme are embarking for the real application in the resource-limited environment.