Patent ID: 7526287

Claim:
A method of transmitting data for a broadcast service from a Core Network (CN) in a mobile communication system including the CN for providing broadcast services, at least one Universal Mobile Telecommunications System(UMTS) Terrestrial Radio Access Network (UTRAN) connected to the CN, and at least one User Equipment (UE) for receiving broadcast services through the UTRAN, the method comprising the steps of: transmitting a plurality of ciphering keys, which are generated for encoding data for the broadcast service, to the at least one UE wherein the plurality of ciphering keys are transmitted to the at least one UE through a broadcast service response message; generating a data frame including data encoded using a ciphering key selected from the plurality of the ciphering keys; and transmitting a ciphering key indicator of the selected ciphering key to the at least one UE by incorporating the ciphering key indicator into header information of the generated data frame, wherein the ciphering key used to encode the data is changed at intervals of a predetermined period.