CRGC -- A Practical Framework for Constructing Reusable Garbled Circuits

TL;DR

This paper introduces a practical framework for constructing reusable garbled circuits that enable efficient multiple evaluations, with some privacy tradeoffs, and demonstrates significant performance improvements over existing methods.

Contribution

The paper presents two novel schemes for reusable garbled circuits, including a fully reusable and a partially reusable version, with implementations and benchmarks showing substantial speed and size advantages.

Findings

CRGC evaluation is up to 20 times faster than existing libraries.

CRGC can process approximately 80 million gates per second for conversion.

A compressed CRGC is about 75% smaller than the original circuit.

Abstract

In this work, we introduce two schemes to construct reusable garbled circuits (RGCs) in the semi-honest setting. Our completely reusable garbled circuit (CRGC) scheme allows the generator (party A) to construct and send an obfuscated boolean circuit along with an encoded input to the evaluator (party B). In contrast to Yao's Garbled Circuit protocol, B can securely evaluate the same CRGC with an arbitrary number of inputs. As a tradeoff, CRGCs predictably leak some input bits of A to B. We also propose a partially reusable garbled circuit (PRGC) scheme that divides a circuit into reusable and non-reusable sections. PRGCs do not leak input bits of A. We benchmark our CRGC implementation against the state-of-the-art garbled circuit libraries EMP SH2PC and TinyGarble2. Using our framework, evaluating a CRGC is up to twenty times faster, albeit with weaker privacy guarantees, than evaluating an equivalent garbled circuit constructed by the two existing libraries. Our open-source library can convert any C++ function to a CRGC at approx. 80 million gates per second and repeatedly evaluate a CRGC at approx. 350 million gates per second. Additionally, a compressed CRGC is approx. 75% smaller in file size than the unobfuscated boolean circuit.