Add descrambling technology is used to encrypt and decrypt digital programming. The basic principle is to use the control word scrambling encryption transmission method, using IC card to decrypt the client.
In the MPEG transport stream, transport-related and control words have two data streams: authorization control information (Elms) and authorization management information (Emmis). By the service key (SK) encrypted control words in Elms after the transfer, including program source, time, content classification program information and program price.
On the control word encrypted service key information in the transfer authorization management, and key business users to go through before sending personal distribution of key (PDE) of the encryption processing. Emmis also includes addresses, user authorization information, such as the user can watch the program or time period, users pay subscription fees and so on. User profile assigned key (PDK) stored in the user's smart card (Smart Card), in the client, dream box boxes based on PMT and CAT tables CA-descriptor, to obtain the PID value of the EMM and ECM, and then filter out from the TS stream Elms and Emmis, and sent through the Smart Card Interface Smart Card.
Smart Card user profile assigned to read the first key (PDK), with the PDK to the EMM decrypting, remove the SK, then use SK to decrypt on the ECM, remove the CW, and CW Smart Card interface, given by descrambling engine, descrambling engine CW can be used have been scrambling to descramble the transport stream.
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