cryptosystem

Abstract

The present invention provides a secret-key functional encryption technology capable of proving removal of a function key. The present invention comprises: a master secret key generation device that generates a master secret key SKL.msk from a security parameter λ and the number q of function keys that can be issued; a key generation device that generates a function key SKL.fsk~ and a verification key SKL.vk from the master secret key SKL.msk, a function f, and the number n of ciphertexts available until removal of the function key; an encryption device that generates ciphertext SKL.ct from the master secret key SKL.msk and plaintext x; a decryption device that generates plaintext y from the function key SKL.fsk~ and the ciphertext SKL.ct; a certificate generation device that generates, from the function key SKL.fsk~, a certificate SKL.cert for proving removal of the function key SKL.fsk~; and a certificate verification device that generates, from the verification key SKL.vk and the certificate SKL.cert, a result rslt of verifying the certificate SKL.cert with the verification key SKL.vk.