Abstract
In 2004, Ku et al. proposed an improved efficient remote authentication scheme using smart cards to repair the security pitfalls found in Chien et al.'s scheme, in which only few hashing operations are required. Later, Yoon et al. presented an enhancement on Ku et al.'s scheme. Recently, Wang et al. showed that both Ku et al.'s scheme and Yoon et al.'s scheme are still vulnerable to the guessing attack, forgery attack and denial of service (DoS) attack. Then, proposed an efficient improvement over Ku et al.'s and Yoon et al.'s schemes with more security. In this paper, we state that Wang et al.'s scheme is vulnerable to the impersonation attack and parallel session attack. A modification to enhance the security of Wang et al.'s scheme is proposed. Our scheme is suitable for applications with high security requirement. © 2009 Springer-Verlag Berlin Heidelberg.