A Simple and Efficient Re-Scrambling Scheme for DTV Programs

In order to guarantee pay-TV services, data of digital television (DTV) programs are scrambled by conditional access systems (CAS). In practical applications, some DTV transmitting nodes need descramble the scrambled DTV programs for editing purposes. After editing, how to re-scramble these edited programs is a challenging task since building CAS at transmitting nodes is expensive and insecure. In this paper, we proposed a novel scheme to solve this problem. Together with the recommended scheme, we also proposed techniques regarding video key data selection and extraction, synchronization of scrambled and descrambled transport stream (TS) packets, and scrambled/unscrambled interleaving multiplexer. The proposed scheme requires much lower complexity than existing methods while maintaining enough security for practical applications. Neither professional CAS equipment nor real-time common key (CK) transmitting is required by our re-scrambling scheme. Various experimental results demonstrated that the proposed re-scrambling scheme achieved superior performance in practical DTV systems, and it also obtained good compatibility with different CAS algorithms.