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Abstract

In a television receiver for a transmission system in which the video signal is scrambled to allow only for its authorized reception, a video signal processor (8) is provided in which the scrambled video signal is de-scrambled. A low rate encrypted signal present at an output (11) of a sound/data signal processor (10) is decrypted and employed to periodically set (say once every one or two seconds) a master pseudo ramdom pulse generator (12B) producing an output of pseudo random configuration at the frame rate which is used to periodically set a video slave pseudo random pulse generator (15) to produce an output of pseudo random configuration at line frequency. This is applied to an input S of the processor (8) and forms the scrambling key for the line-by-line de-scrambling of the video signal. The sound/data components, which are packet multiplexed, are also scrambled at packet rate to allow only for their authorized reception, the sound/data signal processor (10) additionally performing the descrambling of the sound/data components. The output of the master pseudo random generator (12B) is also used to periodically set a number of slave pseudo random pulse generators (17, 18, 19) which produce outputs of pseudo random configuration at packet frequency applied to inputs S1, S2S3 of the processor (10) and which form the respective scrambling packet keys for the de-scrambling of the scrambled sound/data components. The advantage obtained is that a low rate encryption key need only be transmitted to produce the required scrambling keys for both video and sound/data.

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First Claim