Password Authentication Scheme Preserving Identity Privacy

Recently, the authentication schemes based on password have been used widely in network environment. It provides a convenient way for users to authenticate him/her to servers. Previously, Xu et al. proposed an improved smart card based password authentication scheme with provable security. Unfortunately, Song pointed out their scheme cannot withstand impersonation attacks. Moreover, Song proposed two improved schemes to solve it, but his first scheme still cannot withstand impersonation attack. This paper in addition to analyze the weakness of Song's scheme, improved scheme preserving identity privacy also proposes.