PAY TELEVISION SYSTEM, METHOD FOR TRANSMISSION OF SCRAMBLED AUDIOVISUAL PROGRAMMES, DECODER AND CHIP FOR CARRYING OUT SAID METHOD

摘要

The invention relates to a method for broadcasting a scrambled audiovisual programme to decoders (11), comprising a step for transmission of first messages (ECM) to said decoders, each comprising a control word (CW), encrypted using a operation key permitting each decoder to unscramble the received audiovisual programme during a given period, second messages (EMM) comprising operation keys according to which during the same basic period as the scrambling time for the scrambled audiovisual programme, there is transmission of at least two first messages, each containing the same control word respectively encrypted by distinct operation keys and second messages, each containing one of said operation keys and an individual or group address of at least one decoder of the at least two decoder units.