Security Analysis of Timestamp-based Remote User Authentication Scheme Using Smart Cards

recently, Shen, Lin, and Hwang proposed a modified Yang-Shieh's password authentication scheme to enhance security. In 2004, Yang and Chen et al. point out that Shen-Lin-Hwang's scheme was vulnerable to the forged login attack. Later, Wang and Li present a new efficient timestamp-based remote user authentication scheme via further modified Shen-Lin-Hwan's scheme. And they also claimed that their new modified scheme could withstand the forged login attack. However, in this paper, we show that the Yang and Li`s improvement scheme is still vulnerable to the reflection attack, and propose our improvement scheme.