PURPOSE: To transmit communication texts to the other party of communication while concealing contents of communication texts from intermediate repeater stations by putting a ciphered text, which is preliminarily acknowledged between a transmitter and receiver, in the address position of data of one transmission unit.
CONSTITUTION: A pair of a enciphering key K 302 and a deciphering key K' 305 are made different from each other. A normal text M 301 is enciphered with the enciphering key K 302 by a enciphering part 303, and this enciphered text EK (M) 304 is deciphered with the deciphering key K' 305 by a deciphering part 306 to obtain an original normal text M 307. The enciphering key K 302 and the deciphering key K' 305 are generated in a receiver 308, and the enciphering key K 302 is opened to a transmitter 309, and the deciphering key K' 305 is held secretly by the receiver 308.
SASAKI RYOICHI
SHIRAISHI TAKAYOSHI
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