Dragos Rotaru, KU Leuven and University of Bristol

Abstract

The obvious step in building a universal framework is the ability to switch between LSSS (linear secret sharing schemes) when there is a high number of rounds due to many non-linear operations to constant round protocols such as Garbled Circuits (GC). Currently, this can be done efficiently when the parties act semi-honestly (ABY) or with three parties and an honest majority (ABY3).

We provide a new construction for multiparty share conversion resistant against a dishonest majority which is competitive with a weaker adversary such as ABY or ABY3. Our construction (denoted Marbled Circuits) uses LSSS and GC in a generic way and allows to connect the best protocol for dishonest majority for arithmetic circuits with the fastest protocol for garbling boolean circuits. To realize this we introduce a new preprocessing form called daBits - random bits authenticated in both worlds (LSSS and GC). These daBits can also be used in various access structures such as MPC with honest majority and active security.

In this talk we investigate the difficulties we encounter when trying to integrate our share conversion method into a fully-fledged system such as SCALE-MAMBA (S&M). Since S&M supports multiple LSSS with various access structures and connects different types of online phases with their specific preprocessing material it seems to be an ideal candidate for Marbled Circuits.

In the end we argue the case that if the research community focuses on fully integrating the preprocessing material for different protocols then it would become more easier to build complex protocols on top of them. Furthermore, these protocols can be later used by people outside our research bubble we often find ourselves in.

Video