Function private functional encryption and property preserving encryption: New de and positive results. Cryptology ePrint Archive, Report 2013/744

This work furthers the exploration of meaningful definitions for security of Functional Encryption. We propose new simulation based definitions for function privacy in addition to data privacy and study their achievability. In addition, we improve efficiency / underlying assumptions / security achieved by existing inner product Functional Encryption and Property Preserving Encryption schemes, in both the private and public key setting. Our results can be summarized as follows: • We present a new simulation based definition, which we call Relax-AD-SIM, that lies between simulation based (SIM) and indistinguishability based (IND) definitions for data privacy, and implies the function privacy definition of [BRS13a]. Our definition relaxes the requirements on the simulator to bypass impossibility of SIM in the standard model. We show that the inner product FE scheme of [KSW08] enjoys Relax-AD-SIM security for function hiding and the inner product FE scheme of [LOS+10] enjoys Relax-AD-SIM security for data hiding. • We study whether known impossibilities for achieving strong SIM based security imply actual real world attacks. For this, we present a new UC-style SIM based definition of security that captures both data and function hiding, both public key and symmetric key settings and represents th