A more Secure and Practical Remote User Authentication Scheme for Multi-server Environment

We study many schemes based on dynamic ID for multi-server environment, especially Lee et al.'s. However, we find Lee et al.'s scheme still cannot resist Denial of Service (DoS) attack, insider attack. In addition, the user cannot select the server to login due to the design flaws. In this paper, we propose a new scheme to optimize Lee et al.'s scheme. The proposed scheme resists DoS attack by increasing a local validation step and resists insider attack by encrypting the random number stored in the smart card. What's more, the proposed scheme makes up the defects in selecting server by increasing the server's identity. The calculation cost of the proposed scheme is four hash operations more than Lee at al.'s scheme. We increase less than 10% calculation cost to make up for the deficiency of Lee at al.'s scheme.