有線電視系統中對於頻道保護的金匙分配方法

Abstract

有線電視系統是指用戶端藉由付費而能夠收看電視節目的商業電視系統。 而在這裡所謂的頻道保護，目的在於保證只有付費的合法用戶才能收看到 電視頻道上的節目，而不合法的用戶則沒有能力收看。在許多實際的系統 中的做法，電視節目在傳送到用戶端之前已先經由攪亂器加以加密保護， 只有合法的用戶才擁有解密金匙而正確地解回原來的電視節目。而為了更 安全的考量，這些金匙需要經常地加以更新。將更新的金匙各別地傳送給 合法的用戶是相當沒有效率的做法。在本論文中，我們對於幾種不同的情 況總共提出了三個金匙發送方法，目的都是將更新的金匙安全而有效率地 傳送給合法的用戶端。在這些方法中，都只需要一個或兩個訊息的傳送就 可達到所有用戶更新金匙。而且只用到簡單的運算，如對稱型加解密運算 、單向函數以及XOR函數，適合實作於使用智慧卡的系統中。 A Pay-TV system is a commercial TV system, which charges its subscribers for receiving the TV programs. The purpose of channel protection is to insure that only the authorized subscribers, who have paid the fee, can watch the TV programs, while an unauthorized viewer can see nothing intelligible. In many real systems, TV programs are scrambled before broadcasting, and only the authorized subscribers will get the keys to descramble the original TV programs correctly. For higher security consideration, thekeys should be updated constantly. It is a very inefficient way to send the updated keys to each subscriber respectively. In this thesis, we proposed three key distribution schemes for different situations in order to efficiently and securely distribute the keys to the authorized subscribers. In these schemes, only one or two messages are transmitted for updating the keys, and only simple computation functions, i.e. the symmetric key encryption/ decryption function, the one-way function and the XOR function, are adopted for implementation in the smart card-based systems.