CBMC-GC: An ANSI C Compiler for Secure Two-Party Computations

Secure two-party computation (STC) is a computer security paradigm where two parties can jointly evaluate a program with sensitive input data, provided in parts from both parties. By the security guarantees of STC, neither party can learn any information on the other party’s input while performing the STC task. For a long time thought to be impractical, until recently, STC has only been implemented with domain-specific languages or hand-crafted Boolean circuits for specific computations. Our open-source compiler CBMC-GC is the first ANSI C compiler for STC. It turns C programs into Boolean circuits that fit the requirements of garbled circuits, a generic STC approach based on circuits. Here, the size of the resulting circuits plays a crucial role since each STC step involves encryption and network transfer and is therefore extremely slow when compared to computations performed on modern hardware architectures. We report on newly implemented circuit optimization techniques that substantially reduce the circuit sizes compared to the original release of CBMC-GC.