A communications network encryption system

摘要

A communication network comprises a plurality of radio terminals 1 each having an encryption key controller 3. An encryption system used with the network has an allocated number of encryption keys, said number being one more than the number of terminals in the network. Each terminal is allocated all but one of the allocated number of encryption keys so that each terminal has a different omitted encryption key. Encryption is carried out using a key which is common to all of the terminals and if one of the terminals is stolen, the key omitted from the stolen terminal may be used to update the remaining terminals. In this manner the network may be kept secure even if a large number of terminals are stolen or lost over a period of time.