L1 - An Intermediate Language for Mixed-Protocol Secure Computation

Secure Computation (SC) enables secure distributed computation of arbitrary functions of private inputs. It has many useful applications, e.g. benchmarking or auctions. Several general protocols for SC have been proposed and recently been implemented in a number of compilers and frameworks. These compilers or frameworks implement one general SC protocol and then require the programmer to implement the function he wants the protocol to compute. Performance remains a challenge for this approach and it has been realized early on that special protocols for important problems can deliver superior performance. In this paper we propose a new intermediate language (L1) for optimizing SC compilers which enables efficient implementation of special protocols potentially mixing several general SC protocols. We show by three case studies - one for computation of the median, one for weighted average, one for division - that special protocols and mixed-protocol implementations in our language L1 can lead to superior performance. Moreover, we show that only a combined view on algorithm and cryptographic protocol can discover SCs with best run-time performance.