Password-based two-party authenticated key exchange (2PAKE) protocol enables two or more entities, who only share a low-entropy password between them, to authenticate each other and establish a high-entropy secret session key. Recently, Zheng et al. proposed a password-based 2PAKE protocol based on bilinear pairings and claimed that their protocol is secure against the known security attacks. However, in this paper, we indicate that the protocol of Zheng et al. is insecure against the off-line password guessing attack, which is a serious threat to such protocols. Consequently, we show that an attacker who obtained the users' password by applying the off-line password guessing attack can easily obtain the secret session key. In addition, the protocol of Zheng et al. does not provide the forward secrecy of the session key. As a remedy, we also improve the protocol of Zheng et al. and prove the security of our enhanced protocol in the random oracle model. The simulation result shows that the execution time of our 2PAKE protocol is less compared with other existing protocols. . 4898 M. S. FARASH, S. H. ISLAM AND M. S. OBAIDAT known-key secrecy and perfect forward secrecy [23-25]. To deal with the problems, Arshad et al. proposed an authentication scheme [25] based on the elliptic curve cryptography (ECC). But, Tang et al. [26] demonstrated the vulnerability of the scheme of Arshad et al. to the off-line password guessing attack and introduced an improved scheme to overcome the identified weakness.In 2010, Yoo et al. [27] also proposed an authentication scheme based on the ECC to deal with the problems in the scheme of Tsai et al. [22]. In 2012, Xie [28] pointed out that the scheme of Yoo et al. still suffers from the stolen-verifier and off-line password guessing attacks and proposed an improved scheme. However, Farash and Attari [29] showed that Xie's scheme is also insecure and then they designed an enhanced scheme. In 2013, Zhang et al. [30] proposed a new password-based authenticated protocol, but Tu et al. [31] found out that it is insecure against the impersonation attack. Tu et al. then proposed an improved scheme for session initiation protocol (SIP) using smart card to overcome the security flaws of the protocol of Zhang et al..In 1999, Seo and Sweeney [32] have designed a password-based 2PAKE protocol, however, Tseng [33] has shown that the replay attack is possible in the scheme [32] and then proposed an improved 2PAKE protocol. In 2000, Ku and Wang [34] analyzed that Tseng's 2PAKE protocol is still vulnerable to a kind of replay attack and then they designed an improved protocol to eliminate the attack found in [34]. In 2003, Chang et al. [35] demonstrated that Ku and Wang's protocol is still defenseless to the modification attacks and then proposed an enhanced 2PAKE protocol. However, in 2010, Cheng et al. [36] pointed out that the protocol of Chang et al. is vulnerable against the replay attack and the off-line password guessing attack. Recently, Zheng et al. [37] proposed a password-based 2PAKE protoc...
