Security Improvement on a Remote User Authentication Scheme Using Smart Cards

Authentication is a very important ingredient service for the network system to verify whether a remote user is legal through any insecure channel. Recently. Hsiang and Shih proposed a remote user authentication scheme as an improved scheme over Yoon-Ryu-Yoo's, and asserted that their scheme could escape from masquerade attack, parallel session attack, etc. In this paper, we show that Hsiang and Shih's scheme still suffers from parallel session attack. To mend the problem, we offer a procedure to improve Hsiang and Shih's scheme. Consequently, our scheme is suitable for applications with higher secure requirement.