Cryptographic system, encryption device, re-encryption key generation device, re-encryption device, and cryptographic program

Abstract

An encryption deviceoutputs 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 chas been set with one of attribute information y and attribute information z related to each other. A decryption deviceoutputs a re-encryption key rk including a decryption key k, a decryption key k, and encrypted conversion information ϕ. The decryption key kis 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. The decryption key khas been set with the other one of the attribute information y and the attribute information z. The encrypted conversion information ϕis obtained by encrypting the conversion information Wby setting one of attribute information x' and attribute information v′ related to each other. A re-encryption deviceoutputs a re-ciphertext ret including a ciphertext cand a decryption key k. The ciphertext cis obtained by setting one of additional information H and additional information Θ to the ciphertext ct. The decryption key kis obtained by setting the other one of the additional information H and the additional information Θ to the re-encryption key rk.