WYS*: A Verified Language Extension for Secure Multi-party Computations
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Secure multi-party computation (MPC) enables a set of mutually distrusting parties to cooperatively compute, using a cryptographic protocol, a function over their private data. This paper presents WYS*, a new domain-specific language (DSL) implementation for writing MPCs. WYS* is a Verified, Domain-Specific Integrated Language Extension (VDSILE), a new kind of embedded DSL hosted in F*, a full-featured, verification-oriented programming language. WYS* source programs are essentially F* programs written against an MPC library, meaning that programmers can use F*'s logic to verify the correctness and security properties of their programs. To reason about the distributed semantics of these programs, we formalize a deep embedding of WYS*, also in F*. We mechanize the necessary metatheory to prove that the properties verified for the WYS* source programs carry over to the distributed, multi-party semantics. Finally, we use F*'s extraction mechanism to extract an interpreter that we have proved matches this semantics, yielding a verified implementation. WYS* is the first DSL to enable formal verification of source MPC programs, and also the first MPC DSL to provide a verified implementation. With WYS* we have implemented several MPC protocols, including private set intersection, joint median, and an MPC-based card dealing application, and have verified their security and correctness.
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