Improved Delegation-Based Authentication Protocol for Secure Roaming Service with Unlinkability

Recently, Lee et al. proposed a delegation-based authentication protocol which provides secure and private roaming service for portable communication systems in global mobility networks. In this paper, we show that 1) Lee et al.´s protocol cannot protect users´ privacy even though the protocol provides the user identity privacy; and 2) the unlinkability is required for delegation-based authentication protocols to provide user privacy. Moreover, we propose an improved protocol with the unlinkability by modifying Lee et al.´s protocol.