A method for minimizing overhead occurring caused by control information
for encryption performed to protect MBMS data for an MBMS service in a
mobile communication system. This method is implemented by distinguishing
a case in which control information used for encryption is updated from
another case in which the control information used for encryption is not
updated, and transmitting different control information according to the
distinguishment result. That is, when the control information used for
encryption is not updated, only minimized control information is
transmitted, and when the control information for encryption is updated,
the entire updated control information is transmitted. Accordingly, the
amount of control information transmitted along with MBMS data is
minimized, contributing to an increase in the amount of MBMS data
transmitted per unit time.