As cable systems evolve, they will handle diverse information sources such as revenue-generating programs (pay-per-view events), video-text, computer games and two-way services. To ensure the revenue generating potential of such services and to prevent unauthorized reception of signals, the sender and/or receiver may scramble or encrypt the signals.
In this paper, an overview of video scrambling techniques is provided. Each technique is assessed in terms of its scrambling depth (degree to which recognizability of an image is destroyed), security (degree to which the technique resists pirating), residual effects in descrambled video and coexistence with other scrambling schemes - in selected cases, computer simulation results are included to demonstrate the efficacy of the scrambling technique. Cost performance tradeoffs for each scrambling technique and future trends in scrambling are also discussed.