According to the present invention, a homomorphic public key cryptography is achieved in which encryption cannot be performed with a homomorphic operation execution authorization, by separating an encryption execution authorization and the homomorphic operation execution authorization in the homomorphic public key cryptography. The encryption system comprises: a key generation device which generates an encryption key related to an authorization to generate a ciphertext from a plaintext, a homomorphic operation key which is related to an authorization to execute a homomorphic operation of a ciphertext while being encrypted, and has weaker authorization than the encryption key, and a decryption key related to an authorization to decrypt the ciphertext; an encryption device which generates a ciphertext from a plaintext by using the encryption key; a homomorphic operation device which executes a homomorphic operation on the ciphertext by using the homomorphic operation key; and a decryption device which decrypts the ciphertext by using the decryption key.
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