Cryptanalysis of Two Dynamic ID-Based Remote User Authentication Schemes for Preserving User Privacy

Remote user authentication is an essential part in electronic commerce to identify legitimate users over the Internet. However, how to protect user privacy in the authentication has become an important issue recently. Therefore, many secure authentication schemes with smart cards have been proposed. In this paper, we will analyze the security weaknesses of two recently proposed authentication schemes for preserving user privacy. First, Chang et al. (2011) proposed a robust and efficient remote user authentication scheme to provide user anonymity. However, this scheme fails to protect user privacy in terms of anonymity and traceability. In addition, it is vulnerable to the server counterfeit attack and it does not provide perfect forward secrecy for session keys. Furthermore, if the smart card is lost, it will suffer from the offline password guessing attack as well as the user impersonation attack. Second, Wen and Li (2012) recently presented an improved dynamic ID-based authentication scheme with key agreement. However, this scheme is vulnerable to traceability. In addition, it does not support perfect forward secrecy for session keys. Furthermore, the insecure offline password change phase and online secret renewal phase will result in the denial of service attack.