International Association
for Cryptologic Research

In recent years, a lot of progress has been made on speeding up Actively-secure Two-party Function Evaluation (SFE) using Garbled Circuits. For a given level of security, the amount of information that has to be sent and evaluated has been drastically reduced due to approaches that optimize the garbling method for the gates (such as Free-XOR, Flex-OR and Half-Gates). Moreover, the total number of garbled circuits sent to the evaluator dropped by a factor of 3, mostly due to the Forge-and-Lose-technique. In another line of work, Frederiksen et al. introduced the first special purpose garbling technique, namely a garbling scheme without privacy guarantees.

In this note, we present an approach to combine such a privacy-free garbling scheme with an arbitrary SFE protocol for a certain class of circuits, such that the overall protocol is actively secure. This then yields a SFE protocol that has a smaller overhead in total. We instantiate our approach with the SFE protocol by and show that the combination of both allows saving substantial amounts of network bandwidth for certain classes of circuits.