Method for protecting broadcast frame, terminal for authenticating the broadcast frame and access point for broadcasting the broadcast frame

A method for protecting a broadcast frame, a terminal for authenticating the broadcast frame and an AP(Access Point) for broadcasting the broadcast frame are provided to check effectiveness of a key via a symmetric encryption scheme and to authenticate a BMF(Broadcast Management Frame) as soon as the BMF is received. A method for protecting a broadcast frame comprises the following two steps. An AP broadcasts a beacon and an MBF(Maintenance Beacon Frame) to plural terminals for an MBWP(Maintenance Beacon Waiting Period). The AP broadcasts at least BMF during a BMFWP(Broadcast Maintenance Beacon Waiting Period). The step S310 can be divided into two following sub-steps. The AP generates the MBF including a previous key for a previous beacon cycle, a beacon message integrity code, a BMF number transmitted to a current beacon cycle and a message integrity code(S311) and broadcasts the MBF to the plural terminals(S312).