Abstract: This paper proposes an enhanced authentication model, which is suitable for low-power mobile devices. It uses an Extended Password Key Exchange Protocols [2] and elliptic-curve-cryptosystem based trust delegation mechanism to generate a delegation pass code for mobile station authentication, and it can effectively defend all known attacks to mobile networks including the denial-of-service attack. Moreover, the mobile station only needs to receive one message and send one message to authenticate itself to a visitors location register, and the model only requires a single elliptic-curve scalar point multiplication on a mobile device. Therefore, this model enjoys both computation efficiency and communication efficiency as compared to known mobile authentication models.