Towards Verifying Ethereum Smart Contracts at Intermediate Language Level

Abstract

Smart contracts have exhibited great potential in a spectrum of applications, ranging from digital currency to online gaming. Yet smart contracts are known to be prone to errors and vulnerable to attacks. The validation of smart contracts before their deployment is an indispensable step for their correctness and security, and the highest level of guarantee can be provided using formal verification. The level of difficulty, reliability, etc., of the formal verification of a smart contract is deeply affected by the programming language in which the contract is implemented. In this paper, we discuss the benefits of verifying smart contracts at the level of intermediate languages, in comparison with machine-level languages and user-level languages. We augment the existing formalization of Yul – the intermediate language of Ethereum, realize an ERC20 token contract in this language, and verify the guarantees of all the functions provided by this contract. All this development has been performed in the proof assistant Isabelle/HOL. It demonstrates the feasibility and some of the most important advantages of mechanized verification for smart contracts at the intermediate-language level, such as a balance between the intuitiveness of the verification target and the ability to validate lower-level mechanisms like the function dispatcher.