An Exquisite Authentication Scheme with Key Agreement Preserving User Anonymity

In 2009, Liao et al. proposed an exquisite mutual authentication scheme with key agreement using smart cards to access a network system legally and securely. Liao et al.'s scheme adopted a transformed identity (TID) to avoid identity duplication. However, we find out that an adversary may exploit TID to achieve offline guessing attack. Liao et al.'s scheme is also exposed to man-in-the-middle attack and their claimed theorems and proofs are incorrect. We conduct detailed analysis of flaws in the scheme and its security proof. This paper proposes an improved scheme to overcome these problems and preserve user anonymity that is an issue in e-commerce applications.