关键词: 密钥交换协议, 可证明安全, 口令认证, 离线字典攻击

Abstract: Password authenticated key exchange protocol can be used for two parties sharing only a low-entropy password to establish high entropy shared keys.It has been extensively studied for its great application prosperity.In this paper，cryptanalysis of a protocol proposed by Shu et al. in the paper of “Provable Secure Encrypted Key Exchange Protocol under Standard Model”，and a protocol proposed by Li et al. in the paper of“Verifier-Based Password Authenticated Key Exchange for Three Party” has been presented.Concrete off-line dictionary attacks in which an outside adversary traverses the password dictionary and verifies its guess in off-line manner are also presented.Further，the errors in the original security proof are also analyzed.

Key words: key exchange protocol, provable security, password authenticated, off-line dictionary attack