CIPHER SYSTEM, ENCRYPTION DEVICE, RE-ENCRYPTION KEY GENERATION DEVICE, RE-ENCRYPTION DEVICE, AND CIPHER PROGRAM

摘要

An encryption device 200 outputs a ciphertext ct including a ciphertext c and a ciphertext c ~ . The ciphertext c has been set with one of attribute information x and attribute information v related to each other. The ciphertext c ~ has been set with one of attribute information y and attribute information z related to each other. A decryption device 300 outputs a re-encryption key rk including a decryption key k *rk , a decryption key k ~*rk , and encrypted conversion information Æ rk . The decryption key k *rk is obtained by converting the decryption key k * which is set with the other one of attribute information x and attribute information v, with conversion information W 1,t . The decryption key k ~*rk has been set with the other one of the attribute information y and the attribute information z. The encrypted conversion information Æ rk is obtained by encrypting the conversion information W 1,t by setting one of attribute information x' and attribute information v' related to each other. A re-encryption device 400 outputs a re-ciphertext rct including a ciphertext c renc and a decryption key k *renc . The ciphertext c renc is obtained by setting one of additional information H and additional information ˜ to the ciphertext ct. The decryption key k *renc is obtained by setting the other one of the additional information H and the additional information ˜ to the re-encryption key rk.