Abstract: A key authentication method between a user equipment (UE) and a serving network (SN) for binary CDMA network and a key re-authentication method during which the UE performs a handover within the same SN in binary CDMA network are provided. The key authentication method for the user equipment includes receiving a terminal authentication request message from a wireless access point, transmitting a terminal authentication response message that includes identification information for the user terminal, receiving user authentication request message that includes at least two random numbers and code information for message authentication from the wireless access point, and transmitting a user authentication response message that comprises first information that is generated using a master key.