1. A method of controlling the simultaneous broadcast of enciphered digital information signals to a plurality of subscribers in which each subscriber has a permanent box enciphering key; in which the broadcast digital information signal is in a service enciphering key; and in which communication to subscribers may take place in a group enciphering key common to a group of subscribers having a common interest in the reception of broadcast signals of a particular type, including the steps of: (a) simultaneously broadcasting digital information signals in a specific service key, which digital information signals are deciphered by subscribers having the service key, (b) changing the service key at subscribers by simultaneously communicating the change in service key to subscribers in at least a portion of a group, such communication being in the group enciphering key, (c) changing the group enciphering key in at least a portion of the subscribers in a group by communicating such change in the group enciphering key to the selected subscribers in the group, with each communication to a subscriber in the group being preceded by an address to designated subscribers in the group.