Abstract.Recently, Amin and Biswas proposed a novel authentication protocol for TMIS. They claimed that their protocol provides security protection on the attacks proposed by them. Even though Amin and Biswas's protocol achieves efficiency, we demonstrate that their protocol is insecure against many attacks. To overcome the defects in Amin and Biswas's protocol, we proposed an improved user authentication scheme in TMIS. The security analysis shows that the proposed protocol remedies the weaknesses in Amin and Biswas's protocol.

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Abstract. Recently, after analyzing Jiang et al. and He et al.'s remote user authentication scheme, Kumari et al. detected some defects in their own protocol and designed a user anonymous password authentication scheme without smart card. They claimed that their protocol is rigorous to resist a wide range of network attacks. Unfortunately, based on the analysis of a large amount of experiments, we found that their protocol is not robust enough when facing with changing session key attack. The user and server cannot achieve the consistency of the session even though they have been authenticated each other.