CIPHERING METHOD, CIPHERING DEVICE, DECIPHERING METHOD, DECIPHERING DEVICE, CIPHER COMMUNICATION METHOD, CIPHER COMMUNICATION SYSTEM, COMPUTER PROGRAM AND RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To provide a highly safe public key ciphering system which includes a ciphering method that is strong against a connection key attack and a difference key attack and a deciphering method that is strong against a selection cipher sentence attack.;SOLUTION: A plain sentence is converted into a converted plain sentence on the basis of a prescribed conversion function, and a ciphered sentence is formed using the converted plain sentence, the original plain sentence and one or a plurality of public keys. When a plurality of deciphered results exists after deciphering the inputted ciphered sentence, computations similar to the ciphering of the ciphered sentence being inputted to the deciphering results are performed employing a secret key and a deciphered result which agrees with the original plain sentence is obtained from a plurality of deciphered results on the basis of the computation result.;COPYRIGHT: (C)2003,JPO