Research And Implementation Of Scrambling And Conditional Access System

Conditional access is the process of determining which individual digital receivers shall be able to deliver particular broadcast programs to end users. It is an essential part of the business of pay television and therefore vital to the development of successful digital television businesses. Scrambling system is a key technology in conditional access system which scrambles data in the MPEG-2 Transport Stream. And in-depth research is made in this thesis. After analyzing some practical issues, I design and implement a scrambling and conditional access system with full functions, appropriate size and certain application field.There maybe several CA systems (CASs) in a SimulCrypt CAS. Each CAS manages its subscribers independently. The Control Word (CW) and scrambling algorithm used to scramble the Transport Stream (TS) is same to different CASs. The difference is just the mechanism to send CWs to the consumer.The scrambling and multiplexing is the key of CAS. In this thesis in-depth analyze is made to how to achieve high scrambling and multiplexing velocity. During the hardware implement, in-depth analyze is made to traditional distribute Algorithm (DA) and a improvement algorithm is made. In the thesis, a good performance is gained with implement four 256 state machines by making good use of residuary block RAM in FPGA chip. In present dissertation, TS sync Flag is got rapid-extract by software and hardware cooperation and whether packet length is 188 or 204 bytes also is distinguished. using soft flag, hardware modify PCR field in the TS packet. And a common interface is used to implement cipher algorithm subrogation.Whether exact synchronization can be achieved affects the performance of the SimulCrypt system. In this thesis in-depth analyze is made to synchronization issues in SimulCrypt system and some way are give. The Cipher Algorithm issues include: The synchronization between activating theCW and broadcasting the relevant ECM; The synchronization between activating the work key and the key is used to decrypt the CW. In present dissertation, by sending odd and even CWs simultaneously, along with then odd and even CW flag in TS packet header, the difference between adjacent CWs would be very clear. And send odd and even work keys in turn. It not only makes the difference between adjacent work keys clear, but also reduces whole quantity of data. The CA band and how to organizing the EMM and ECM information is key issue in the SimulCrypt system. In this thesis, A common distributed key scheme is adopt to meet consumer.In the end, system and electrocircuit simulation is analyzed detailedly.