Establishing Cooperative Computation with Hardware Embassies

While recent cryptographic techniques enable cooperative multi-party client-server computations under mutual distrust, they also introduce an efficiency tradeoff. Hosting all of the computation from the different parties involved on one set of servers requires everyone to agree on which servers are trustworthy. On the other hand, keeping the computations truly distributed introduces significant delays because of the inherently latency-sensitive nature of the protocols involved. In this paper, we explore the architectural impact of a possible middle path to this problem: resource-poor but physically secure devices interacting with significant (but not mutually trusted) compute and storage resources. The idea is that a small and well-protected "Embassy" can serve as a plot of sovereign soil in an otherwise untrusted environment. Building on techniques from multiparty computation (MPC) we show how such an architecture, even when extremely limited in size, can leverage local network capabilities and asymmetries in cryptographic operations to perform more efficient interactive secure computations. Even with a client-side device 5x slower, we show that common MPC applications can still be accelerated by 3x on average. Moreover, we explore the potential for architectural changes to further support multi-party evaluation through the addition of dedicated evaluator hardware further improving performance 1.52x.