Patent ID: 8086851

Claim:
Method for broadcasting a scrambled multimedia program by way of a broadband network, wherein: information can be routed to a multicast address so that only one group of several terminals corresponding to this multicast address receives the information while other terminals connected to the same network do not receive this information, and information can be routed to a unicast address so that only the terminal corresponding to this unicast address receives the information while the other terminals connected to the same network do not receive it, and wherein a network head: scrambles the multimedia program with a control word, encrypts the control word in order to obtain a first cryptogram, encrypts the first cryptogram in order to obtain a second cryptogram, the first and second encryptions being effected by means of different encryption keys selected from the group composed of a processing key (K Proc ) and a license key (K Term ), multiplexes the second cryptogram with the scrambled multimedia program to obtain multiplexed contents, broadcasts the multiplexed contents to a multicast broadcast address in order to establish a point-to-multipoint connection between the network head and several receivers of the multiplexed contents, and on a point-to-point link established with a terminal using the unicast address of this terminal, transmits the license key individually to this terminal by way of this point-to-point link, characterized in that, before the transmission of the license key: the network head carries out a step of authenticating the terminal, and if the terminal has been successfully authenticated, the network head sends to the terminal a license transmission message containing the license key or a cryptogram of the license key, by way of the point-to-point link established, and if the terminal is not successfully authenticated, the network head acts in such a manner as to prevent the complete unscrambling by this terminal of the scrambled multimedia program broadcast; wherein the network head carries out a phase of establishing a secure tunnel on the point-to-point link established, during which, if the terminal has been successfully authenticated: the network head establishes, by random selection, a session key common to the terminal and to the network head, then sends to the terminal the license transmission message encrypted with this session key.