| 摘要 |
PURPOSE:To eliminate the need of always holding a terminal key by a host and to contrive the economization by allowing the host to have an arithmetic means of an algorithm F, determining the terminal key from a terminal code of a terminal and allowing the terminal to have a terminal key storage means. CONSTITUTION:For instance, a central office H1 of a host side generates terminal keys Ki, Kj by using an algorithm F, and also, enciphers a communication key R by using the terminal keys Ki, Kj as keys and obtains cipher texts Ci, Cj. The central office H1 sends the cipher Ci to a telephone set Ti, and sends the cipher Cj to a telephone set Tj. The telephone set Ti knows a fact that the cipher text Ci has been sent and receives the cipher text Ci. Subsequently, by using the terminal key Ki which has been held in a terminal key storage means, the cipher text Ci is decoded and the communication key R is obtained. In the same way, the telephone set Tj decodes the cipher text Cj by using the terminal key Kj which has been held and obtains the communication key R. In such a way, it is unnecessary that the central office H1 holds beforehand the terminal keys Ki, Kj. |
