| 摘要 |
PURPOSE:To sufficiently secure the secrecy of communication information by a method wherein a key is generated at each subscriber's terminal, and a central unit and the subscriber's terminal encode a communication information to be transmitted by means of an exclusive logical sum processing based on said key. CONSTITUTION:From a subscriber's terminal, an encoding key for the secrecy generated by an encoding key generation circuit 18 is transmitted to the central unit, and the information signal to be transmitted to the central unit is encoded through the exclusive logical sum operation in an exclusive logical sum circuit by using a scramble data generated based on the coding key. At the central unit, the encoding key transmitted from the terminal is stored in a encoding key holding circuit 27; the exclusive logical sum circuit decodes and fetches the information signal encoded and transmitted from the subscriber's terminal by using a scramble data generated based on the encoding key, and further, the information signal is encoded through an exclusive logical summing then is transmitted to the subscriber's terminal. In such a way, the secrecy of a communication information can be effectively attained.
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