2021 年 E104.A 巻 7 号 p. 968-978
In this paper, we put forward the notion of a token-based multi-input functional encryption (token-based MIFE) scheme - a notion intended to give encryptors a mechanism to control the decryption of encrypted messages, by extending the encryption and decryption algorithms to additionally use tokens. The basic idea is that a decryptor must hold an appropriate decryption token in addition to his secrete key, to be able to decrypt. This type of scheme can address security concerns potentially arising in applications of functional encryption aimed at addressing the problem of privacy preserving data analysis. We firstly formalize token-based MIFE, and then provide two basic schemes; both are based on an ordinary MIFE scheme, but the first additionally makes use of a public key encryption scheme, whereas the second makes use of a pseudorandom function (PRF). Lastly, we extend the latter construction to allow decryption tokens to be restricted to specified set of encryptions, even if all encryptions have been done using the same encryption token. This is achieved by using a constrained PRF.
