Homomorphic arithmetic unit, cryptographic system and homomorphic arithmetic program

摘要

An encryption device generates a ciphertext ct including an encryption element C in which a plaintext μ is set, an encryption element Cx in which an attribute x is set, and an encryption element F that is not to be decrypted with a decryption key skf corresponding to a policy f satisfied by the attribute x and in which the plaintext μ is set. A homomorphic computation device converts the ciphertext ct into a ciphertext ct˜ by converting, with the encryption element F, the encryption element C included in the ciphertext ct into an encryption element C˜ that can be decrypted with the decryption key skF corresponding to a policy set F acquired by a policy acquisition unit. The homomorphic computation device performs homomorphic computation g on the ciphertext ct˜ to generate a ciphertext ct*.