In 1999, Hwang and Li proposed a new user authentication scheme using smart cards. The scheme does not need any password or verification table. Later, Sun proposed an efficient remote use authentication scheme to improve the efficiency of the Hwang-Li scheme. However, these two schemes do not allow users to freely choose and change their passwords. In this article, we shall propose a simple and efficient remote user authentication scheme that allows users to freely choose and change their passwords without significantly increasing the computation cost.
