On the Relationship between Functional Encryption, Obfuscation, and Fully Homomorphic Encryption.

We investigate the relationship between Functional Encryption FE and Fully Homomorphic Encryption FHE, demonstrating that, under certain assumptions, a Functional Encryption scheme supporting evaluation on two ciphertexts implies Fully Homomorphic Encryption. We first introduce the notion of Randomized Functional Encryption RFE, a generalization of Functional Encryption dealing with randomized functionalities of interest in its own right, and show how to construct an RFE from a standard semantically secure FE. For this we define the notion of entropically secure FE and use it as an intermediary step in the construction. Finally we show that RFEs constructed in this way can be used to construct FHE schemes thereby establishing a relation between the FHE and FE primitives. We conclude the paper by recasting the construction of RFE schemes in the context of obfuscation.