Weaknesses of the Yoon-Kim-Yoo remote user authentication scheme using smart cards

A user authentication scheme is a mechanism employed by a server to authenticate the legality of a user before he/she is allowed to access the resource or service provided by the server. Due to the Internet's openness and lack of security concern, the user authentication scheme is one of the most important security primitives in the Internet activities. Many researchers have been devoted to the study of this issue. There are many authentication schemes have been proposed up to now. However, most of these schemes have both the advantages and disadvantages. Recently, Yoon, Kim and Yoo proposed a remote user authentication scheme which is an improvement of Liaw et al.'s scheme. Unfortunately, we find their scheme is not secure enough. In this paper, we present some flaws in Yoon-Kim-Yoo's scheme. This proposed cryptanalysis contributes important heuristics on the secure concern when researchers design remote user authentication schemes.