Semantic Understanding of Smart Contracts: Executable Operational Semantics of Solidity

Abstract

Bitcoin has been a popular research topic recently. Ethereum (ETH), a second generation of cryptocurrency, extends Bitcoin's design by offering a Turing-complete programming language called Solidity to develop smart contracts. Smart contracts allow creditable execution of contracts on EVM (Ethereum Virtual Machine) without third parties. Developing correct and secure smart contracts is challenging due to the decentralized computation nature of the blockchain. Buggy smart contracts may lead to huge financial loss. Furthermore, smart contracts are very hard, if not impossible, to patch once they are deployed. Thus, there is a recent surge of interest in analyzing and verifying smart contracts. While most of the existing works either focus on EVM bytecode or translate Solidity smart contracts into programs in intermediate languages, we argue that it is important and necessary to understand and formally define the semantics of Solidity since programmers write and reason about smart contracts at the level of source code. In this work, we develop a formal semantics for Solidity which provides a formal specification of smart contracts to define semantic-level security properties for the high-level verification. Furthermore, the proposed semantics defines correct and secure high-level execution behaviours of smart contracts to reason about compiler bugs and assist developers in writing secure smart contracts.