Formal Verification of Ethereum Smart Contracts Using Isabelle/HOL

Abstract

AbstractThe concept of blockchain was developed with the purpose of decentralizing the trade of assets, suppressing the need for intermediaries during this process, as well as achieving a digital trust between parties. A blockchain consists in a public immutable ledger, constituted by chronologically ordered blocks such that each block contains records of a finite number of transactions.The Ethereum platform, that this paper builds upon, is implemented using a blockchain architecture and introduces the possibility of storing Turing complete programs. These programs, also known as smart contracts, can then be executed using the Ethereum Virtual Machine. Despite its core language being the EVM bytecode, they can also be implemented using a higher-level language that is later compiled to EVM, being Solidity the most used. Among its applications stand out decentralized information storage, tokenization of assets, and digital identity verification.In this paper we propose a method for formal verification of Solidity smart contracts in Isabelle/HOL. We start from the imperative language and big-step semantics proposed by Schirmer [23], and adapt it to describe a rich subset of Solidity, implementing it using the Isabelle/HOL proof assistant. Then, we describe the properties about programs using Hoare logic, and present a proof system for the language, for which results on soundness and (relative) completeness are obtained.Finally, we describe the verification of an electronic voting smart contract, which illustrates the degree of proof complexity that can be achieved using this method. Examples of smart contracts containing overflow and reentrancy vulnerabilities are also presented.KeywordsFormal verificationIsabelle/HOLHoare logicSmart contractsSolidityEthereum