In order to scramble as effectively as possible pay-television transmissions, the transmitter is made to transmit, at one and the same time, access messages and entitlement messages, all of them crypted and corresponding to a control word periodically loaded into a pseudo-random generator. In each receiver,...http://www.google.ca/patents/US5224161?utm_source=gb-gplus-sharePatent US5224161 - Method of scrambling and of unscrambling composite video signals, and device for implementation
