Building Executable Secure Design Models for Smart Contracts with Formal Methods

Abstract

Smart contracts are appealing because they are self-executing business agreements between parties with the predefined and immutable obligations and rights. However, as with all software, smart contracts may contain vulnerabilities because of design flaws, which may be exploited by one of the parties to defraud the others. In this paper, we demonstrate a systematic approach to building secure design models for smart contracts using formal methods. To build the secure models, we first model the behaviors of participating parties as state machines, and then, we model the predefined obligations and rights of contracts, which specify the interactions among state machines for achieving the business goal. After that, we illustrate executable secure model design patterns in TLA+ (Temporal Logic of Actions) to against wellknown smart contract vulnerabilities in terms of state machines and obligations and rights at the design level. These vulnerabilities are found in Ethereum contracts, including Call to the unknown, Gasless send, Reentrancy, Lost in the transfer, and Unpredictable state. The resultant TLA+ specifications are called secure models. We illustrate our approach to detect the vulnerabilities using a real-estate contract example at the design level. I.

Blockchain E Smart Contracts Como Ferramentas De Gestão Na Tributação Da Prestação De Serviços Digitais

“…Smart contracts é uma tecnologia que foi desenvolvida pelo cientista da computação Nich Szabo em 1994, em uma tentativa de criar contratos digitais, que fossem automáticos e não necessitassem de terceiros para sua execução (Tönnissen & Teuteberg, 2018). Por definição, trata-se de códigos auto executáveis, que agem automaticamente quando ocorrem suas regras predefinidas (Xu & Fink, 2019). Em geral, eles têm por objetivo satisfazer uma condição contratual (regra), tal como execução automática de condições de pagamento, garantias, confidencialidade e obrigações, minimizando exceções (acidentais ou propositais) e a necessidade de intermediários e confiança para execução do protocolo (Szabo, 1997).…”

A Survey of Smart Contract Formal Specification and Verification

“…Set-based modeling frameworks Event-B and TLA+ utilize set theory and logic to formally specify systems, and have been applied on smart contracts as well. Analogically to other formal languages, such as PN, set-based frameworks support the tools for model analysis, making them useful in the implementation of correct-by-design smart contracts [31,211] and verification of the existing ones [223]. While efficient for checking of safety properties, set-based formalisms lack the expressiveness to reason about progress, e.g., liveness properties.…”

“…TLA+ is a formal specification language for concurrent systems. That allows Xu et al [211] to model behaviors of interacting participants of a legal smart contract. Although the authors of [211] do not translate their TLA+ specification to executable code, they propose a set of design patterns to protect them from common security vulnerabilities of smart contracts.…”

“…Although the authors of [211] do not translate their TLA+ specification to executable code, they propose a set of design patterns to protect them from common security vulnerabilities of smart contracts. In general, the set-based correctness requirements for smart contracts specify values allowed to be taken by contract variables [31,223], possible states of contract participants [211], or the users that are authorized to invoke contract functions [223]. Xu et al [211] also verify whether events representing the actions of contract parties are permitted according to the legal contract.…”

“…In general, the set-based correctness requirements for smart contracts specify values allowed to be taken by contract variables [31,223], possible states of contract participants [211], or the users that are authorized to invoke contract functions [223]. Xu et al [211] also verify whether events representing the actions of contract parties are permitted according to the legal contract.…”