Abstract: Television programs are broadcast to a plurality of receiver units in various geographic areas. Each unit has a memory for storage of a designation code representative of its location and a memory for the storage of a blackout tier indication. Prior to the transmission of the program to be blacked out, each unit is separately addressed and provided with a message including a designation code for storage. Then, a globally addressed message provides all receiver units having a selected designation code with a blackout tier indication for storage. A program tier indication is transmitted along with the program to be blacked out. Each unit, upon receiving the transmitted program, compares the transmitted program tier indication and the blackout tier indication in its memory. All receiver units having a stored blackout tier indication which matches the program tier indication are simultaneously prevented from displaying the program to be blacked out.

Abstract: A cryptographic system is used for the secure transmission of digitized signals to a plurality of receivers. At the transmission end, a key consisting of two blocks, each including a plurality of key fragments, is generated. For each transmission session, different sets of key fragments may be periodically selected from one of the key blocks and used to encrypt the signals. Data indicative of the set selection is generated. The key is distributed to each receiver. The set selection data is transmitted to all receivers along with the encrypted signals and used to construct the key fragment set for decryption of the transmitted signals. During the transmission session, the other key block may be varied to form a replacement key which is distributed to each receiver. At the end of the session, the functions of the key blocks are interchanged in all receivers at one time by selecting a set in the varied key block for use in encryption and decryption.

Abstract: Audio and control signals are digitized and inserted in the horizontal blanking intervals of the distributed composite television signal. The control signals are in the form of a data stream which includes a header containing group address, sync, and program-related information applicable to all receiving units, and a plurality of portions which are addressable to and contain information applicable to the control of particular individual receiving units in the addressed group. The information in the addressable portions can be altered on a real time basis such that the system operator has direct control over certain functions of individual receiving units from the transmission end.

Abstract: A cryptographic system is used for the secure transmission of digitized signals to a plurality of receivers. At the transmission end, a key consisting of two blocks, each including a plurality of key fragments, is generated. For each transmission session, different sets of key fragments may be periodically selected from one of the key blocks and used to encrypt the signals. Data indicative of the set selection is generated. The key is distributed to each receiver. The set selection data is transmitted to all receivers along with the encrypted signals and used to construct the key fragment set for decryption of the transmitted signals. During the transmission session, the other key block may be varied to form a replacement key which is distributed to each receiver. At the end of the session, the functions of the key blocks are interchanged in all receivers at one time by selecting a set in the varied key block for use in encryption and decryption.