zkHawk: Practical Private Smart Contracts from MPC-based Hawk

TL;DR

This paper introduces zkHawk, a practical private smart contract protocol that replaces trusted managers with MPC, enhancing privacy and efficiency in blockchain-based smart contracts.

Contribution

It presents a novel MPC-based approach for private smart contracts that reduces overhead and eliminates the need for trusted managers, improving privacy and practicality.

Findings

Achieves privacy for smart contract inputs without trusted parties

Uses lightweight MPC and cryptographic proofs to ensure correctness

Demonstrates practical implementation with low overhead

Abstract

Cryptocurrencies have received a lot of research attention in recent years following the release of the first cryptocurrency Bitcoin. With the rise in cryptocurrency transactions, the need for smart contracts has also increased. Smart contracts, in a nutshell, are digitally executed contracts wherein some parties execute a common goal. The main problem with most of the current smart contracts is that there is no privacy for a party's input to the contract from either the blockchain or the other parties. Our research builds on the Hawk project that provides transaction privacy along with support for smart contracts. However, Hawk relies on a special trusted party known as a manager, which must be trusted not to leak each party's input to the smart contract. In this paper, we present a practical private smart contract protocol that replaces the manager with an MPC protocol such that the function to be executed by the MPC protocol is relatively lightweight, involving little overhead added to the smart contract function, and uses practical sigma protocols and homomorphic commitments to prove to the blockchain that the sum of the incoming balances to the smart contract matches the sum of the outgoing balances.