Password-based authenticated key exchange(PAKE) protocols are cryptographic primitives which enable two entities,who only share a memorable password,to identify each other and to communicate over a public unreliable network with a secure session key.In this paper,we propose a simple,efficient and provably secure PAKE protocol based on Diffie-Hellman key exchange and cryptographic hash function.Our protocol is secure against dictionary attacks.Its security is proved based on the hardness of the computational Diffie-Hellman problem in the random oracle model. Password-based authenticated key exchange (PAKE) protocols are cryptographic primitives which enable two entities, who only share a memorable password, identify each other and to communicate over a public unreliable network with a secure session key. In this paper, we propose a simple, efficient and provably secure PAKE protocol based on Diffie-Hellman key exchange and cryptographic hash function. Our protocol is secure based on the hardness of the computational Diffie-Hellman problem in the random oracle model.