In 2005, Liu et al. proposed an improvement to Chien et al.＇s remote user authentication scheme, using smart cards, to prevent parallel session attack. This article, however, will demonstrate that Liu et al.＇s scheme is vulnerable to masquerading server attack and has the system＇s secret key forward secrecy problem. Therefore, an improved scheme with better security strength, by using counters instead of timestamps, is proposed. The proposed scheme does not only achieve their scheme＇s advantages, but also enhances its security by withstanding the weaknesses just mentioned.
The traditional authentication system is based on the secret key, and is mainly based on public key infrastructure （PKI）. Unfortunately, a key has many disadvantages, for example, the key can be forgotten or stolen, and can be easily cracked. Nowadays, authentication systems using biometric technology have become more prevalent because of the advantages over password-based authentication systems. In this article, several biometfic authentication models are presented, upon which most biometric authentication systems are based. Biometric authentication systems based-on these models provide high security for access control in non-face-to-face environment such as e-commerce, over open network.
