Controlled functional encryption

3École polytechnique fédérale de Lausanne Motivated by privacy and usability requirements in various sce-narios where existing cryptographic tools (like secure multi-party computation and functional encryption) are not adequate, we in-troduce a new cryptographic tool called Controlled Functional En-cryption (C-FE). As in functional encryption, C-FE allows a user (client) to learn only certain functions of encrypted data, using keys obtained from an authority. However, we allow (and require) the client to send a fresh key request to the authority every time it wants to evaluate a function on a ciphertext. We obtain efficient solu-tions by carefully combining CCA2 secure public-key encryption (or rerandomizable RCCA secure public-key encryption, depend-ing on the nature of security desired) with Yao’s garbled circuit. Our main contributions in this work include developing and for-mally defining the notion of C-FE; designing theoretical and prac-tical constructions of C-FE schemes achieving these definitions for specific and general classes of functions; and evaluating the perfor-mance of our constructions on various application scenarios