Abstract: A method for efficiently deriving a traffic encryption key for data encryption is disclosed. A method of generating a traffic encryption key (TEK) comprises the steps of receiving, by a mobile station from base station, a first nonce and first security materials for deriving the traffic encryption key (TEK) and deriving the traffic encryption key (TEK) using one or more of the first nonce, the authentication key (AK), and the first security materials.

Abstract: A pre-authentication method for an Inter-RAT handover is disclosed. This pre-authentication method relates to a wireless access system, and provides a method for performing pre-authentication in case of an inter-RAT handover managed by different administrative domains. The method for performing pre-authentication before a handover in order to quickly perform an Inter-Radio Access Technology (Inter-RAT) handover, includes, transmitting a message having terminal information needed for the pre-authentication to a target authentication server, receiving security-associated information of a target network from the target authentication server, wherein the target network security-associated information is generated by the mobile terminal information, and generating security-associated information, which will be used by the mobile terminal in the target network, using the security-associated information of the target network, and performing the pre-authentication.