Homomorphic arithmetic unit, cryptographic system and homomorphic arithmetic program

摘要

The encryption device (30) decrypts the decryption key skf corresponding to the policy f in which the plaintext μ is set, the cryptographic element Cx in which the attribute x is set, and the plaintext μ in which the plaintext μ is satisfied. Generate a ciphertext ct including the cryptographic element F that is not stored. The homomorphic arithmetic unit (40) converts the cryptographic element C included in the ciphertext ct into a cryptographic element C which can be decrypted by the cryptographic element F using the decryption key skF corresponding to the policy set F acquired by the policy acquisition unit. By converting, the ciphertext ct is converted to the ciphertext ct ̃. The homomorphic arithmetic unit (40) performs homomorphic operation g on the ciphertext ct ̃ to generate a ciphertext ct *.