Large Scale, Actively Secure Computation from LPN and Free-XOR Garbled Circuits

We present a secure multiparty computation (MPC) protocol based on garbled circuits which is both actively secure and supports the free-XOR technique, and which has communication complexity O(n) per party. This improves on a protocol of Ben-Efraim, Lindell and Omri which only achieved passive security, without support for free-XOR. Our construction is based on a new variant of LPN-based encryption, but has the drawback of requiring a rather expensive garbling phase. To address this issue we present a second protocol that assumes at least n/c of the parties are honest (for an arbitrary fixed value c). This second protocol allows for a significantly lighter preprocessing, at the cost of a small sacrifice in online efficiency. We demonstrate the practicality of our evaluation phase with an implementation.