Extracting smart contracts tested and verified in Coq

Abstract

We implement extraction of Coq programs to functional languages based on MetaCoq's certified erasure. As part of this, we implement an optimisation pass removing unused arguments. We prove the pass correct wrt. a conventional call-by-value operational semantics of functional languages. We apply this to two functional smart contract languages, Liquidity and Midlang, and to the functional language Elm. Our development is done in the context of the ConCert framework that enables smart contract verification. We contribute a verified boardroom voting smart contract featuring maximum voter privacy such that each vote is kept private except under collusion of all other parties. We also integrate property-based testing into ConCert using QuickChick and our development is the first to support testing properties of interacting smart contracts. We test several complex contracts such as a DAO-like contract, an escrow contract, an implementation of a Decentralized Finance (DeFi) contract which includes a custom token standard (Tezos FA2), and more. In total, this gives us a way to write dependent programs in Coq, test them semi-automatically, verify, and then extract to functional smart contract languages, while retaining a small trusted computing base of only MetaCoq and the pretty-printers into these languages.

Extracting functional programs from Coq, in Coq

“…Being written in Coq gives us a significant advantage since it makes it possible to apply various techniques to verify the development itself. The current work extends and improves the results previously published and presented by the same authors at the conference Certified Programs and Proofs (Annenkov et al, 2021) in January 2021. We build on the ConCert framework (Annenkov et al, 2020;Nielsen and Spitters, 2019) for smart contracts verification in Coq and the MetaCoq project (Sozeau et al, 2020).…”

“…The present work builds on and extends the ConCert smart contract certification framework presented by the three authors of the present work at the conference Certified Programs and Proofs in January 2020 (Annenkov et al, 2020). In this section, we describe the overall structure of ConCert focusing on the parts, relevant for the present work, and extensions developed in (Annenkov et al, 2021) and in the present work.…”

“…However, we also provide executable implementations of the specification that execute the outgoing call in depth-first or breadth-first order (see (Nielsen and Spitters, 2019) for more details). The executable implementations are especially useful for techniques like property-based testing that we have explored in our previous work (Annenkov et al, 2021).…”

A verified algebraic representation of cairo program execution

“…Jiao et al [23] and Ribeiro et al [28] verify programs written in a subset of Solidity with respect to a high-level description of the semantics, and Bhargavan et al [11] verify smart contracts written in Solidity by translating them to F ★ . Annenkov et al [6] provide means of defining and verifying smart contracts in Coq and then extracting code for various blockchain platforms. A number of systems provide means of verifying the correctness of cryptographic protocols and their implementations, including [1ś4, 9,12,29].…”

A verified algebraic representation of Cairo program execution

“…Jiao et al [16] and Ribeiro et al [20] verify programs written in subset of Solidity with respect to a highlevel description of the semantics, and Bhargavan et al [7] verify smart contracts written in Solidity by translating them to F ⋆ . Annenkov et al [3] provide means of defining and verifying smart contracts in Coq and then extracting code for various blockchain platforms. At the other end of the chain, Abate et al [1] provide means of verifying the correctness of cryptographic protocols.…”