Wireless network authentication schemes have been researched for about a decade, and associated security problems explored by many researchers. In 2004, Zhu and Ma proposed an authentication scheme for wireless environments. Afterwards other researchers proposed improvements according to Zhu-Ma scheme. Mutual authentication is one of the most important issues. To the best of our knowledge, there is no scheme that allows a foreign agent to authenticate the home agent and mobile user at the same time. Towards this purpose, we propose a simultaneous authentication scheme based on chaotic maps, and describe how our proposed scheme addresses various security problems while maintain anonymity.