An Improved Remote User Authentication Scheme Using Smart Cards
  In 2000, Hwang and Li proposed a new remote user authentication scheme using smart cards. In the same year, Chan and Cheng pointed out that Hwang and Li&#8217;s scheme is not secure against the masquerade attack. Further, in 2003, Shen, Lin and Hwang pointed out a different type of attack on Hwang and Li&#8217;s scheme and presented a modified scheme to remove its security pitfalls. This paper presents an improved scheme which is secure against Chan-Cheng and all the extended attacks. 
Manoj Kumar