Telecommunications network, in particular mobile radio network, with network-uniformly changeable keys

• Main Authors: G.,. DIEDERICH,HANS, LOGEMANN,HELMUT
• Format: Patent
• Language: English; German
• Published: 13.03.1986
• Edition: 4
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHICCOMMUNICATION; WIRELESS COMMUNICATIONS NETWORKS

In a telecommunications network, in particular a mobile radio network, with a plurality of subscriber terminal devices and at least one central station, the encryption provided for data prone to misuse, such as subscriber identifiers, is intended to be modified by the central station in a network-uniform manner in the event of the key becoming known. For this purpose, a key memory SP containing n keys is provided in each subscriber terminal device with an activation signal decoder ASD connected upstream in order to decode n-1 key addresses. In the event of misuse of the initially used first key being detected, a network-uniform activation signal AS which is inserted in a concealed manner in the useful signal is transmitted by the central station over a relatively long time period to the subscriber terminal devices, said activation signal providing one of the subsequent n-1 keys instead of the first key. The activation signal AS can be concealed in the useful signal in time division multiplexing, e.g. through permutation of an address bit in an address block which is inserted in the useful bit stream and is otherwise occupied with blank bits, or in frequency division multiplexing, e.g. through the addition of sub-audio frequencies to the useful band. For network-wide modification of the key once it has become known, the address of the key memory SP is modified by the activation signal AS in the central station only (Fig.).