M-Sel: A Message Selection Functional Encryption from Simple Tools

In this paper, we put forward a new practical application of Inner-Product Functional Encryption ( \(\textsf{IPFE}\) ) that we call Message Selection functional encryption ( \(\textsf{M}\text {-}\textsf{Sel}\) ) which allows users to decrypt selected portions of a ciphertext. In a message selection functional encryption scheme, the plaintext is partitioned into a set of messages \(M = \{m_1,\ldots ,m_t\}\) . The encryption of M consists in encrypting each of its elements using distinct encryption keys. A user with a functional decryption key \(sk_{\boldsymbol{x}}\) derived from a selection vector \(\boldsymbol{x}\) can access a subset of M from the encryption thereof and nothing more. Our construction is generic and combines a symmetric encryption scheme and an inner product functional encryption scheme, therefore, its security is tied to theirs. By instantiating our generic construction from a DDH-based IPFE we obtain a message selection FE with constant-size decryption keys suitable for key storage in lightweight devices in the context of Internet of Things (IoT).