Binary Information Press
Recently, the researchers proposed a dynamic ID-based scheme of user authentication over multi-server environments. Their scheme allows a user to register only once at the registration center and then he can access all the servers. Although they assumed that the Registration Center (RC) is reliable, some risks may occur on the service providers. The main reason of these risks is that all servers share the same master keys. Once one of the servers has been compromised, the system is not secure anymore.