Abstract: An improved method is proposed in order to solve problems of EAP-AKA protocol.It implements mutual authentication between 3G networks and WLAN access networks by adding shared keys，which can be proved through strand space model and authentication test，the protection to IMSI by transmitting the encrypted NAI and the secure updating of shared keys between users and 3G networks by introducing key updating strategy.

Key words: Extensible Authentication Protocol-Authentication and Key Agreement（EAP-AKA）, 3G, Wireless Local Area Network（WLAN）, strand space, authentication test

摘要： 针对EAP-AKA协议中存在的安全问题，提出了改进方案。通过在3G和WLAN接入网络间增设共享密钥实现了两者间的相互认证，并用串空间模型和认证测试方法进行了形式化分析，通过加密传输NAI实现了对IMSI的加密保护，通过引入密钥更新机制实现了对用户和3G网络间的共享密钥的安全更新。

关键词: EAP-AKA, 3G, 无线局域网络, 串空间, 认证测试方法