Password-based key exchange schemes was designed to provide entities communicating over a public network

and only sharing a（short） password with a session key（e.g.

the key was used for data confidentiality and/or integrity）.There has been much interest in password-authenticated key exchange protocol which remains secure even when users choose passwords from a small space of possible passwords

such as a dictionary of English words.A password-based authenticated key exchange scheme was proposed.The analysis shows that the scheme is secure against dictionary attack under the computational Diffie-Hellman intractability assumption

and preserves user privacy and achieves unlinkability.Furthermore

since denial-of-service（DoS） attacks have become a common threat

DoS-resistantance is a design consid-eration and the scheme is proved to be secure against denial-of-service attacks.