SECURITY DEVICE AND HEAD END IN A CONDITIONAL ACCESS SYSTEM AND METHOD FOR CONTROLLING ILLEGAL USE IN THE SAME

摘要

A security device and a head end in a conditional access system and a method for controlling illegal use in the same are provided to efficiently utilize communication resources at a head side by minimizing the load of an EMM message to transmit. In a security device in a conditional access system, a key database stores a user key(UK) allocated peculiarly to a subscriber(350). A decoder sequentially decodes an update key encoded into the user key(UK), a channel management key encoded into the update key, and a control word encoded into the channel management key which are received from a head end(300) side of the conditional access system by using the user key(UK) stored in the key database, and generates a control word(CW).