| 摘要 |
<p>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, S2+L, S3 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.</p> |
