Key Distribution For Conditional Access System In Digital Television System

Digital television (DTV) broadcast platform gives us a lot of new services. Conditional access system (CAS), which can provide an effective system management and user control, is the key technology for DTV operating agencies to carry out pay-TV and a variety of value-added services. With the launch of HD programs, enrichment of programs and rapid growth in the number of users, how to minimize the bandwidth occupied by entitlement message without make sacrifices to security becomes especially important.Firstly, this thesis analyses the characteristic of CAS, and compares two encryption algorithms which are commonly used in CAS. After pointing out that the authorization information bandwidth is one of the key performance indicators of CAS, the thesis discuss the hierarchical encryption technology and key distribution, and propose a four-level key distribution scheme using program grouping and dynamic user grouping to optimizing the subscriber addressing. In the end, the thesis describe the design scheme of front end system in VNS-CAS, including database and entitlement message designing. Four-level key distribution scheme base on program grouping and dynamic user grouping is used in this system. Testing indicates that the system has achieved the basic functions of CAS. Bandwidth analysis indicates that the bandwidth of authorization information in the system is very low and applicable to CA system with a large number of users. Four-level key distribution scheme base on program grouping and dynamic user grouping is feasible and effective.Now this system has passed every test. This thesis offers a significant approach for the design of CAS.