Recently, Zhang and Fang proposed a security analysis and enhancements of 3GPP authentication and key agreement protocol (AP-AKA for short). The enhancements of 3GPP authentication and key agreement protocol is proposed to improve some drawbacks of the current third-generation wireless communications. It also eliminates the need of synchronization between a mobile station and its home network. However, this paper shows that AP-AKA has some drawbacks, including the huge bandwidth consumption between foreign network and the home network, and the overhead of the stored space in the foreign network, and the overloaded home network with authentication of mobile stations. As a result, an extension of AP-AKA is proposed, which improves theses drawbacks, while preserving the superior merits of AP-AKA.
