METHOD AND DEVICE FOR CIPHERING, METHOD AND DEVICE FOR DECIPHERING, RECORDING MEDIUM RECORDING CIPHERING PROGRAM AND RECORDING MEDIUM RECORDING DECIPHERING PROGRAM

PROBLEM TO BE SOLVED: To detect the generation of alteration by generating a cryptographic sentence that is produced by connecting key distribution data, file ciphering data and the value treated by a unidirectional function. SOLUTION: A ciphering device A101 generates open keys and secret keys for key distribution keys and open keys and secret keys for electronic signature keys and registers these open keys in a certifying agency CA 105. Deciphering devices B [i] (i=1,..., n) 102 to 104 generate open keys for key distribution keys and open keys for electronic signature keys and register these keys in the agency CA 105. Prior to conducting a group ciphering, the device A101 requests for the open keys of key distribution keys of the devices B [i] to the agency CA 105, receives the distribution of the certificates of the open keys and distributes cryptographic sentences, that are plural person ciphered, to the devices B [i]. Prior to conducting receiving/deciphering of the sentences, the devices B [i] requests registered open keys of the device A101 to the agency CA 105, receives the distribution of certificates from the agency CA 105 and conducts a plural person deciphering.