Patent ID: 11349654

Abstract:
A key generation device generates a decryption key dkx having a tag-added decryption key and a decryption key adkx. The tag-added decryption key includes a decryption key tdkx in which a key attribute x is set and a tag tgφ required to decrypt a ciphertext with the decryption key tdkx. In the decryption key adkx, the key attribute x is set. An encryption device generates an original ciphertext octy in which a ciphertext attribute y corresponding to the key attribute x is set and which can be decrypted with the tag-added decryption key. A re-encryption key generation device encrypts the decryption key tdkx by an attribute-based encryption scheme using a ciphertext attribute y′, so as to generate a re-encryption key rkx,y′ which is a key for generating a re-encrypted ciphertext rcty′ which can be decrypted with a decryption key adkx′ in which a key attribute x′ corresponding to the ciphertext attribute y′ is set.