Security of Chien et al.'s remote user authentication scheme using smart cards

In 2000, Sun proposed an efficient remote user authentication scheme using smart cards. Recently, Chien et al. pointed out that Sun's scheme only achieves the unilateral authentication and further proposed a new efficient and practical solution to achieve the mutual user authentication. This paper, however, will demonstrate that Chien et al.'s scheme is vulnerable to the parallel session attack. (C) 2003 Elsevier B.V. All rights reserved.