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Cryptanalysis of Tan's Improvement on a Password Authentication Scheme for Multi-server Environments

Smart cards have been applied on password authentication in recent years. A user can input his/her identity and password to require services from the remote server. There are various attacks through an insecure network to obtain a user’s information. Therefore, many schemes are proposed to guarantee secure communication. However, a lot of schemes are not secure. Recently, Tan proposed an improved password authentication using a smart card for multi-server environments. In this paper, we show the weakness of Tan’s scheme, and his scheme cannot resist a password guessing attack.