The Research Of Multilayer Ecryption And Implementation Of The Front System For Digital TV

With the development of technology, the traditional analog TV now is no longer suitable for the trend of today and Digital TV is popular among the ordinary people. Digital TV is gradually replacing analog TV in the future, to meet diverse demanding of user experience. Digital TV Conditional Access System (Conditional Access System, CAS) is a kind of authorization technology, which plays a crucial role to the Digital TV. Encrypting the digital audio and video signal can ensure the interests of authorized users and operators, which makes unauthorized users unable to enjoy the service. With the support of Conditional Access, Digital TV appreciation business can be carried out properly and obtain the favor of a host of users, which ensures the marketization of Digital TV.This article designs Conditional Access System key distribution scheme, aiming to complete authorization management of million level users, and develop a practical and reliable Digital TV front-end CA system.The thesis introduces the profile of digital television at first, the development of Conditional Access technology at home and abroad, the framework and working principle of CAS, and the standard involved in the conditional access data. Then, the common conditional access encryption and decryption algorithms have been studied to select the appropriate algorithm which suits the topic. And the thesis briefly introduces the SimulCrypt and MultiCrypt technology. Then, this dissertation introduces several conventional mechanism of key distribution. By comparing of their features and the number of authorization information, it provides a new four-level key distribution scheme. The new scheme can decrease the authorization data and save the system bandwidth, for adopting user address broadcasting strategy and effectively combining the advantage of dynamic group and three-level key distribution scheme.Furthermore, this thesis studies the DVB digital TV scrambling machine integrated with synchronizer and scrambler. The article defines authorization data in detail and completes information generator EMMG and authorization control generator ECMG two software in VC#. It provides process analysis and some important data to communicate with the scrambling machine. And it gives some necessary support for future system expansion. It has completed the design of interface between EMMG and SMS, which provides the structure of process and the definition of interface. The scheme has designed the main thread of EMMG and carried out the strategy of priority queueFinally, the result shows that two software work stability, complete the generating of authorization information successfully and encryption of the key, and also achieve the desired effect of grouped authorization. The set-top box can decrypt the key and descramble rightly, then the playback is clear and smooth.