A mobile station is provided. The mobile station includes one or more radio transceiver module and a processor. The processor generates an Authorization Key (AK) context including at least one secret key shared with a base station, transmits at least one association negotiation message via the radio transceiver module to the base station to obtain an association of a service flow established by the base station, and generates at least one TEK according to the secret key and an identifier associated with the association. The service flow is established for traffic data transmission with the base station and the TEK is a secret key shared with the base station for encrypting and decrypting the traffic data.