Method for mobile multicast key management using foreign key

A method for managing a mobile multicast key using a foreign key is provided to reduce an authentication delay time for a mobile terminal by previously performing a delegated authentication between multicast secure relay servers in a region where an electric wave of a base station is overlapped. A method for managing a mobile multicast key using a foreign key comprises four steps. In a first step, a list of secure relay servers connected with a base station which an electric wave transmitted to a mobile terminal is overlapped is searched in a first secure relay server which the mobile terminal is subscribed(S410,S420,S430). In a second step, the first secure relay server requests a delegated authentication of the mobile terminal to the searched second secure relay server, and subscribes to a multicast group of the second secure relay server(S440). In a third step, the second secure relay server accepts the authentication, and transmits a foreign group key and the multicast group address information to the first secure relay server(S460). In a fourth step, the second secure relay server encodes a multimedia stream with the foreign group key, transmits to the multicast group address, and performs a remote subscription of the mobile terminal(S470,S491).