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EthVer: Formal Verification of Randomized Ethereum Smart Contracts

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Financial Cryptography and Data Security. FC 2021 International Workshops (FC 2021)

Part of the book series: Lecture Notes in Computer Science ((LNSC,volume 12676))

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Abstract

Despite the great potential capabilities and the mature technological solutions, the smart contracts have never been used at a large scale, one of the reasons being the lack of good methods to verify the correctness and security of the contracts—although the technology itself (e.g. the Ethereum platform) is well studied and secure, the actual smart contracts are human-made and thus inherently error-prone. As a consequence, critical vulnerabilities in the contracts are discovered and exploited every few months. The most prominent example of a buggy contract was the infamous DAO attack—a successful attack on the largest Ethereum contract in June 2016 resulting in $70 mln-worth Ether stolen and the hard fork of the Ethereum network (80% of Ethereum users decided to revert the transaction and hence two parallel transaction histories exist from that event).

The main contribution of this work is the automatic method of formal verification of randomized Ethereum smart contracts. We formally define and implement the translation of the contracts into MDP (Markov decision process) formal models which can be verified using the PRISM model checker—a state of the art tool for formal verification of models. As a proof of concept, we use our tool, EthVer, to verify two smart contracts from the literature: the Rock-Paper-Scissors protocol from K. Delmolino et al., Step by step towards creating a safe smart contract: Lessons and insights from a cryptocurrency lab. and the Micropay 1 protocol from R. Pass, a. shelat, Micropayments for decentralized currencies.

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Notes

  1. 1.

    https://github.com/lukmaz/ethver.

  2. 2.

    https://why3.lri.fr.

  3. 3.

    http://ethereum.org/.

  4. 4.

    http://web3js.readthedocs.io/.

  5. 5.

    Recall that the extended version of the paper as well as the code of EthVer and example contracts are available at https://github.com/lukmaz/ethver.

  6. 6.

    Note that we don’t describe here how to sign messages in Solidity. In fact, Solidity does not provide convenient API for this. The reason is that a private key is required to sign and we rarely want to do this in the contract code, because we do not want to reveal the private keys to public.

  7. 7.

    This is the actual code of computing and verifying the signature \(\sigma = \textsf {sig}(c, r_2, a)\) from the Micropay 1 protocol (cf. Sect. 7).

  8. 8.

    Recall that 1 finney = 0.001 ETH is a denomination of Ether, the currency of Ethereum. For simplicity, we neglect the transaction fees, unless stated otherwise.

  9. 9.

    Examples of the syntax of commitments and signatures in Solidity and web3.js have already been presented in Sect. 2.3 and 2.4.

  10. 10.

    A PRISM model can consists of several modules, each corresponding to a different part of the system and each with a separate set of variables.

  11. 11.

    The same pattern of a two-phase function execution could be accomplished using only the and modules, however because of visibility of the variables in PRISM, the module is needed to correctly pass the arguments of the call.

  12. 12.

    The current version of EthVer is limited to 2-players protocols only. However, all the security claims as well as the formal translation defined in appendix D of the extended version of the paper hold also for protocols with larger number of players. Note that although EthVer accepts only 2-player protocols, it verifies the contract also against the attacks in which more adversarial players join the protocol at the same time.

  13. 13.

    The ETV code of all tested models is available in the project repository, https://github.com/lukmaz/ethver.

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Authors and Affiliations

  1. University of Warsaw, Warsaw, Poland

    Łukasz Mazurek

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  1. Łukasz Mazurek
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Correspondence to Łukasz Mazurek .

Editor information

Editors and Affiliations

  1. University of Michigan–Ann Arbor, Ann Arbor, MI, USA

    Matthew Bernhard

  2. Computer Science and Mathematics, Stirling University, Stirling, UK

    Andrea Bracciali

  3. Imperial College London, London, UK

    Lewis Gudgeon

  4. Norwegian University of Science and Technology, Trondheim, Norway

    Thomas Haines

  5. Ithaca College, Ithaca, USA

    Ariah Klages-Mundt

  6. Department of Computer Science, Georgetown University, Washington, WA, USA

    Shin'ichiro Matsuo

  7. Imperial College London, London, UK

    Daniel Perez

  8. Dipartimento di Matematica, University of Trento, Trento, Trento, Italy

    Massimiliano Sala

  9. Imperial College London, London, UK

    Sam Werner

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Mazurek, Ł. (2021). EthVer: Formal Verification of Randomized Ethereum Smart Contracts. In: Bernhard, M., et al. Financial Cryptography and Data Security. FC 2021 International Workshops. FC 2021. Lecture Notes in Computer Science(), vol 12676. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-63958-0_30

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  • DOI: https://doi.org/10.1007/978-3-662-63958-0_30

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