| Summary: | 碩士 === 國立清華大學 === 資訊系統與應用研究所 === 94 === The pay-TV system becomes one of the popular applications in recent years because of the advancement in modern network technique. The Conditional Access System (CAS) is the essential function to provide the channel protection in pay-TV system. Only the authorized subscribers can precisely receive the TV program, and they were charged by the service provider according to their subscription. In this paper, we defined a new pay-TV model named Flexible-PPC (F-PPC) which allowed subscribers subscribe to a large number of channels and unsubscribed each of them anytime. In order to accomplish the requirements of F-PPC, we also proposed a CAS with a four-level hierarchical key management scheme. The proposed CAS can be applied on a large scale pay-TV system with lots of subscribers and channels. The subscribers can freely choose the channels. Besides, subscribers can subscribe and unsubscribe channels arbitrarily, and the proposed CAS can also revoke illegal subscribers rapidly.
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