| Abstract: | ABSTRACT In 2004, Das et al. proposed a dynamic identity-based remote user authentication scheme using smart cards. This scheme allows users to choose and change their passwords freely, and the server does not maintain any verification table. Das et al. claimed that their scheme is secure against stolen verifier attack, replay attack, forgery attack, dictionary attack, insider attack and identity theft. However, many researchers have demonstrated that Das et al.'s scheme is susceptible to various attacks. Furthermore, this scheme does not achieve mutual authentication and thus cannot resist malicious server attack. In 2009, Wang et al. argued that Das et al.'s scheme is susceptible to stolen smart card attack. If an attacker obtains the smart card of the user and chooses any random password, the attacker gets through the authentication process to get access of the remote server. Therefore, Wang et al. suggested an improved scheme to preclude the weaknesses of Das et al.'s scheme. However, we found that Wang et al.'s scheme is susceptible to impersonation attack, stolen smart card attack, offline password guessing attack, denial of service attack and fails to preserve the user anonymity. This paper improves Wang et al.'s scheme to resolve the aforementioned problems, while keeping the merits of different dynamic identity based smart card authentication schemes. |
