Paper 2021/739 Original: eprint.iacr.org/2021/739 ↗

A New Approach to Garbled Circuits

Abstract

A garbling scheme is a fundamental cryptographic building block with a long list of applications. The study of different techniques for garbling a function, towards optimizing computation and communication complexity, has been an area of active research. Most common garbling techniques work by representing each gate in the circuit as a set of ciphertexts that encrypt its truth table row-by-row. In this work we present a new garbling scheme in the random oracle (RO) model that garbles circuits in the gate-by-gate paradigm by capturing the gate functionality (AND, XOR) as a whole rather than as a set of ciphertexts. The final gate garbling requires $4\kappa$ bits of communication in expectation, 4 RO calls for garbling and 1 RO call for evaluation. We prove that the scheme satisfies privacy in the non-programmable random oracle model and against PPT adversaries. We also show how this scheme can be extended to support free-XOR and garble any gate functionality over binary inputs.