Abstract. User authentication is an important technology to guarantee that only the legal users can access resources from the remote server. The advantages of smart cards are storage and computation abilities. Recently, Li et al. pointed out the security problems of Chen et al's password authentication scheme and they proposed an enhanced smart card based remote user password authentication scheme and claimed it is secure, However, We find that Li scheme is still vulnerable. It cannot resist user impersonation attack and insider attack. Besides, it also suffers from user anonymity violation and clock synchronization problem.
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