In order to solve the session key agreement problem between a mobile user and a network control center, an authenticated key exchange protocol for mobile satellite communication systems which was proved universally composable secure at present was carefully analyzed. It was found that there was some mistake in the proof and the protocol was easy to suffer the data synchronization attack and the key compromise impersonation attack. Furthermore, improvements to overcome the security vulnerabilities of the protocol were proposed. The improved protocol was universally composable secure.
