Ciphering method and device

PURPOSE: To provide a method and a device capable of ciphering the data of a message stream. CONSTITUTION: A ciphering/decoding device 100 generates mutually independent 1st and 2nd random number stream data. Only in a state selecting a bit corresponding to the data of a 2nd random number stream, the data of a 3rd random number stream are generated from the data of the 1st random stream data only by selecting a bit from the data of the 2nd random stream data. Finally exclusive OR between the data of the 3rd random number stream and a ciphered message stream is executed to generate a ciphered data stream. COPYRIGHT: (C)1994,JPO