Digital receiver and method for receiving secure group data

A method for decrypting an encrypted data stream in a broadcast radio frequency signal comprising the steps of:

• defining a plurality of separately selectable decryption keys, each of the decryption keys corresponding to a predetermined variation of a different one of a predetermined plurality of receiver environmental characteristics, wherein each one of the predetermined plurality of receiver environmental characteristics (1) is shared by a common plurality of radio frequency receivers, (2) has a plurality of variations including the predetermined variation, and (3) divides the common plurality of radio frequency receivers into sets of radio frequency receivers based on its own variations, with each such set comprising a plurality of radio frequency receivers and the sets of radio frequency receivers so produced differing from and overlapping those produced by others of the predetermined plurality of receiver environmental characteristics;
• in each of the common plurality of radio frequency receivers, storing a selected set of the plurality of separately selectable decryption keys, each of the stored decryption keys corresponding to a different one of the receiver environmental characteristics and having a value based on one of the variations of the one of the receiver environmental characteristics as determined by the environment of the radio frequency receiver in which it is stored;
• in a selected one of the plurality of radio frequency receivers, receiving a broadcast radio frequency signal comprising a data stream including an encrypted message and a plurality of key selectors, wherein (1) each of the included key selectors identifies a predetermined one of the receiver environmental characteristics and (2) decryption of the encrypted message requires a decryption key corresponding to a predetermined variation of each identified receiver environmental characteristic;
• selecting the stored decryption key corresponding to the receiver environmental characteristic identified by each of the key selectors included in the received signal;
• and
• using the selected decryption keys in decryption of the encrypted message, whereby successful decryption of the message occurs only when the variation of each of the receiver environmental characteristics required for decryption of the encrypted message matches the variation of the corresponding receiver environmental characteristic in the environment of the selected radio frequency receiver.