Outsourcing Secure Two-Party Computation As A Black Box

Secure multiparty computation (SMC) offers a technique to preserve functionality and data privacy in mobile applications. Current protocols that make this costly cryptographic construction feasible on mobile devices securely outsource the bulk of the computation to a Cloud provider. However, these outsourcing techniques are built on specific secure computation assumptions and tools, and applying new SMC ideas to the outsourced setting requires the protocols to be completely rebuilt and proven secure. In this work, we develop a generic technique for lifting any secure two-party computation protocol into an outsourced two-party SMC protocol. By augmenting the function being evaluated with auxiliary consistency checks, we can create an outsourced protocol with low overhead cost. Our implementation and evaluation show that in the best case, our outsourcing additions execute within the confidence intervals of two servers running the same computation, and incur approximately the same communication cost. In addition, the mobile device itself requires minimal communication exchanged over a single round. This work demonstrates that efficient outsourcing is possible with any underlying SMC scheme, and implements an outsourcing protocol that is efficient and directly applicable to current and future SMC techniques.