Security improvement on Yang-Shieh's authentication scheme

Yang and Shieh (1999) proposed a timestamp-based password authentication scheme using smart cards. However, Chan et al. (2002) and Fan et al. (2002) showed its vulnerability to the forged login attacks, respectively. Also Fan gave a slight modification of the original scheme, which however increases the computation cost of the system. In this paper a more efficient modification of the original scheme is proposed to withstand the forged login attacks.