A mobile station, an access point, a gateway apparatus, a base station, and a handshake method thereof for use in a wireless network framework are provided. The wireless network framework comprises a first wireless network comprising the access point, and a second wireless network comprising the gateway apparatus and base station. There is an IP security tunnel between the access point and the gateway apparatus. When the mobile station handovers from the first wireless network to the second wireless network, it transmits a master session key to the gateway apparatus via the access point and the IP security tunnel. Additionally, when the mobile station handovers from the second wireless network to the first wireless network, it transmits a master session key to the access point. As a result, the authentication time, which is needed in handover procedure between the first wireless network and the second wireless network, is reduced effectively.