Abstract: A method for communicating end-to-end encrypted super group information is provided. Temporary address data, which identifies a temporary address on which the super group is to communicate, is transmitted from a gateway to a back-to-back communications device using a direct mode or data message. The back-to-back communications device retrieves an encryption key associated with the temporary address and uses the encryption key to decrypt super group information sent from a networked communications device on the temporary address. The back-to-back communications reverts back to its original encryption key when super group communications are terminated.

Abstract: A decryption apparatus (109) comprises a key stream generator (111) generating a local decryption key stream. It furthermore comprises a synchronization value receiver (201) receiving key stream synchronization values. A synchronization processor (203) implements a state machine which may operate in a synchronized state (303) wherein the communication is decrypted using the local key stream, a non-synchronized state (301) wherein the local key stream is not synchronized, or in an uncertain synchronization state (305) wherein the communication is decrypted using the local key stream and wherein the local key stream is synchronized to each new received synchronization value. The synchronization processor (203) furthermore comprises a transition controller (213) operable to transition from the synchronized state to the non-synchronized state in response to a first criterion and to the uncertain synchronization state in response to a second criterion.

Abstract: A decryption apparatus (109) comprises a key stream generator (111) generating a local decryption key stream. It furthermore comprises a synchronisation value receiver (201) receiving key stream synchronisation values. A synchronisation processor (203) implements a state machine which may operate in a synchronised state (303) wherein the communication is decrypted using the local key stream, a non-synchronised state (301) wherein the local key stream is not synchronised, or in an uncertain synchronisation state (305) wherein the communication is decrypted using the local key stream and wherein the local key stream is synchronised to each new received synchronisation value. The synchronisation processor (203) furthermore comprises a transition controller (213) operable to transition from the synchronised state to the non-synchronised state in response to a first criterion and to the uncertain synchronisation state in response to a second criterion.