| 摘要 |
PURPOSE:To make wiretap of a message difficult even if the call number of a receiver is opened to the public, by allowing a radio calling station to select one of plural kinds of ciphering method of indication information and cipher indication information when the station transmits indication information to the receiver. CONSTITUTION:The person who wants to carry the receiver reports to a radio calling service station, and the call number of the receiver is given to him, and he designates one of ciphering methods. The station writes the call number of the receiver and the designated ciphering method in a file of an electronic exchange. In case that messages are transmitted to the electronic exchange and the receiver, this transmission is performed on a basis of the call number and ciphering information stored in the file. For example, when indication information ''1, 2, 3, 4'' is transmitted to a receiver (d) of call number ''1'', the call number is transmitted in the POCSAG code standard form, but indication information is transmitted after being ciphered by the ''1'' and ''0'' inverting method. When this indication information is transmitted to a receiver (e) of call number ''2'', it is transmitted after being ciphered by the method where information is transmitted in the reverse order in 4-bit units. |
