Research Of The Conditional Access System In Digital Video Broadcasting System

Digital video broadcasting system, which can provide not only many digital programs, but also variety of services, brings valuable opportunities to the traditional broadcast industry. Conditional access system is the key to realize the increment of the DVB system and provides effective system management and subscriber control. It covers many advanced techniques such as system-scheduling management, network, digital coding & decoding, scrambling & descrambling, encrypting & decrypting, multiplexing, modulating & demodulating, set-top box, smart card and some practical database techniques, for example program management, subscriber management and charging management.CAS appeared firstly in western countries, and at present, there are many mature CAS providers who provide complete solutions with various services throughout the world. Facing the impending of the digitalized era, some CAS providers have appeared in China and put some of their products into practical implementation, all of which are immature and should be checked by time.This paper is based on the concise and deep-going survey of CAS, and finished the following three parts:In the first part, the key distribution management of CAS is discussed. Aiming at the drawbacks of variant levels of key hierarchy, this paper describes two four-level schemes of key hierarchy in CAS. Therefore, we analyze the performance of the complete scheme, which shows that this scheme is efficient and suitable for DVB system that provides both PPC and PPV services.Besides, the described complete scheme is also flexible for dynamicmanagement.In the second part, CA subsystem is implemented in the set-top box. We adopt the embedded security module, and introduce a complete solution for the implementation of CA subsystem, and finally finish decoding relevant CA data, interfacing to smart card and communicating between the host and the smart card. The proposed solution, which ensures both security and lowcost, can be used to instruct the practical application.In the third part, the interoperability between different CASs is discussed. DVB common hardware interface is introduced firstly, then an interoperable software solution is described based on the thought of seperating the proprietary parts of CASs. It provides full CA-STB interoperability. Furthermore, it can be introduced relatively easily into future STBs and will require only minimal changes in current CASs.