Pre-payment television system using a memory card associated with a decoder.

ACCORDING TO THE INVENTION, IN RELATION TO THE ISSUE, A NUMBER GENERATOR (10) PROVIDES A RANDOM CODE (XAL) THAT IS SENT TO THE ENTRY OF A MAIN CARD (11) THAT CODES THE CODE ACCORDING TO A DEFAULT KEY (100), THE CODE ASI ENCRYPTED IS BROADCASTED WITH THE VIDEO SIGNAL, A FIRST DEVICE (17) RECEIVES ON ENTRY, ON THE ONE HAND, THE RANDOM CODE (XA) AND, ON THE OTHER, THE CODE ENCRYPTED BY THE MAIN CARD (11) AND EFFECTS A NUMBER COMBINATION DETERMINED BY THESE TWO CODES, CONSTITUTING THIS COMBINATION THE INITIALIZATION WORD OF A PSEUDO-RANDOM GENERATOR (12) INTENDED TO SUPPLY A CODE TABLE INTENDED TO EFFECT THE INTERFERENCE OF THE VIDEO SIGNAL. IN RELATION TO RECEPTION, THE RECEIVED ENCRYPTION CODE IS DECIPHED BY A CUSTOMER CARD (13), A SECOND DEVICE (18) RECEIVES ENTRY, ON THE ONE PART, THE ENCRYPTED CODE AND, ON THE OTHER, THE DECIPHED CODE (XA) BY THE CUSTOMER CARD (13) AND PERFORM A NUMERICAL COMBINATION OF THESE TWO CODES IDENTIFY THAT OF THE FIRST DEVICE (17).