Full-Threshold Actively-Secure Multiparty Arithmetic Circuit Garbling.

In this work, we show how to garble arithmetic circuits with full active security in the general multiparty setting, secure in the full-threshold setting (that is, when only one party is assumed honest). Our solution allows interfacing Boolean garbled circuits with arithmetic garbled circuits. Previous works in the arithmetic circuit domain focused on the two-party setting, or on semi-honest security and assuming an honest majority - notably, the work of Ben-Efraim (Asiacrypt 2018) in the semi-honest, honest majority security model, which we adapt and extend. As an additional contribution, we improve on Ben-Efraim's selector gate. A selector gate is a gate that given two arithmetic inputs and one binary input, outputs one of the arithmetic inputs, based on the value of the selection bit input. Our new construction for the selector gate reduces the communication cost to almost half of that of Ben-Efraim's gate. This result applies both to the semi-honest and to the active security model.