Paper 2021/174

Smart Contracts for Incentivized Outsourcing of Computation

Alptekin Küpçü and Reihaneh Safavi-Naini

Abstract

Outsourcing computation allows resource limited clients to access computing on demand. Various types of clusters, grids, and clouds, such as Microsoft’s Azure and Amazon’s EC2, form today’s outsourced computing infrastructure. A basic requirement of outsourcing is providing guarantee that the computation result is correct. We consider an automated and efficient way of achieving assurance where the computation is replicated and outsourced to two contractors by a smart contract that will decide on the correctness of the computation result, by comparing the two received results. We show that all previous incentivized outsourcing protocols with proven correctness fail when automated by a smart contract, because of copy attack where a contractor simply copies the submitted response of the other contractor. We then design an incentive mechanism that uses two lightweight response-checking protocols, and employ monetary reward, fine, and bounty to incentivize correct computation. We use game theory to model and analyze our mechanism, and prove that it has a single Nash equilibrium, corresponding to the contractors’ strategy of correctly computing the result. Our work provides a foundation for incentivized computation in the smart contract setting and opens new research directions.