| Summary: | 碩士 === 中正理工學院 === 電機工程研究所 === 86 === This research is for " the cryptography system of digital TV " which is designed a three-layers architecture of cryptography system to get a safe and efficient purpose. Besides, there is a " management center " in the architecture, which is designed for combination with the interactive TV.
Besides the basic encoding and decoding functions, this system provide for administering the identification and changing about the authorization. It is also a function for the additional message in this system.
There are three layers in this study. In the first layer, the control word (CW) is used as the initial value of a pseudo-random noise (PN) generator which generates the binary sequence codes which encode the signal in the scrambler.
The second layer, the authorized key (Ma) is used to encode the CW and entitlement parameter (P1), then generates the entitlement control message (ECM).
The third layer, the distribution key is used to encode the Ma and management message (Mm)，and then to generate the entitlement management message (EMM). For the purpose of encoding and decoding quickly, the signals is divided into two parts: the common message (Mc) and the individual message (Mi). One process is using individual key to deal with Mi; the other is using common key to deal with Mc.
The Ma in Mc sends to the decoder in the second layer. The P1 and CW can be decoded in the decoder. The Mm in Mi sends to the processor in the second layer. The P2 to compare with P1 is in the processor.
When the user*s authority is passed，the CW will be sent to the first layer to let the user watch the TV program after the decoding process.
The software simulation had done in the cryptography system. To analyze the characters of the PN sequence, the Borland C language is run in this research.
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