Fair Payments for Outsourced Computations

Initiated by volunteer computing efforts, the computation outsourcing problem can become a compelling application for networked set-top-boxes and mobile devices. In this paper we extend such environments with the ability to provide secure payments in exchange for outsourced CPU cycles. Previous contributions in wired networks have almost exclusively tackled only one side of the problem -- offering incentives for volunteer participation and preventing worker laziness. This makes sense in static environments where reputable outsourcers have little to gain from incorrectly rewarding honest participation. However, this assumption is no longer valid in ad hoc environments, where unique identities are difficult to provide and anyone can outsource computations. In this paper we propose a solution that simultaneously ensures correct remuneration for jobs completed on time and prevents worker laziness. Our solution relies on an offline bank to generate and redeem payments; the bank is oblivious to interactions between outsourcers and workers. In particular, the bank is not involved in job computation or verification. Our experiments show that the solution is efficient: the bank can perform hundreds of payment transactions per second and the overheads imposed on outsourcers and workers are negligible.