Towards Correct Smart Contracts: A Case Study on Formal Verification of Access Control

Abstract

Ethereum is a platform for deploying smart contracts, which due to their public nature and the financial value of the assets they manage are attractive targets for attacks. With asset management as a main task of smart contracts, access control aspects are naturally part of the application itself, but also of the functions implemented in a smart contract. Therefore, it is desirable to establish the correctness of smart contracts and their access control on application and single-function level through formal methods. However, there is no established methodology of formalising and verifying correctness properties of smart contracts. In this work, we make an attempt in this direction on the basis of a case study. We choose an existing smart contract application which aims to ascertain the integrity of binary files distributed over the Internet by means of decentralised identity management and access control. We formally specify and verify correctness at the level of single functions as well as temporal properties of the overall application. We demonstrate how to use verified low-level correctness properties for showing correctness at the higher level. In addition, we report on our experience with existing verification tools.

Pre-deployment Analysis of Smart Contracts -- A Survey

“…To formally verify smart contracts, such framing conditions are provided with formal specifications of contracts. D Functional Annotations are functional pre-and post-conditions that specify what conditions must hold before and after a function executes [17,89,177]. Such annotations are defined with each function according to its specific functionality.…”

“…Such annotations are defined with each function according to its specific functionality. An example of a precondition is to assert that the contract assumes that the sum of individual balances is equal to the total balance [89], or that the caller must have access rights to the function [177]. An example of a post-condition is that a storage variable must not be modified unless certain preconditions are satisfied [177].…”