CRYPTOGRAPHIC SYSTEM, CRYPTOGRAPHIC COMMUNICATION METHOD, ENCRYPTION APPARATUS, KEY GENERATION APPARATUS, DECRYPTION APPARATUS, CONTENT SERVER, PROGRAM, AND STORAGE MEDIUM

摘要

A cryptographic communication technology that is based on predicate encryption and that can operate flexibly is provided. A conversion rule information pair is determined in advance, which has attribute conversion rule information prescribing a conversion rule for converting attribute designation information to attribute information used in a predicate encryption algorithm and predicate conversion rule information prescribing a conversion rule for converting predicate designation information to predicate information used in the predicate encryption algorithm. One kind of conversion rule information included in the conversion rule information pair is used to obtain first attribute information or first predicate information from input information. The first attribute information or the first predicate information is used for encryption. Encryption information is decrypted with a decryption key generated by using second attribute information or second predicate information obtained from user information by using the other kind of conversion rule information.