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Open Access 2021 | OriginalPaper | Chapter

Helmholtz: A Verifier for Tezos Smart Contracts Based on Refinement Types

Authors : Yuki Nishida, Hiromasa Saito, Ran Chen, Akira Kawata, Jun Furuse, Kohei Suenaga, Atsushi Igarashi

Published in: Tools and Algorithms for the Construction and Analysis of Systems

Publisher: Springer International Publishing

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A smart contract is a program executed on a blockchain, based on which many cryptocurrencies are implemented, and is being used for automating transactions. Due to the large amount of money that smart contracts deal with, there is a surging demand for a method that can statically and formally verify them.This tool paper describes our type-based static verification tool Helmholtz for Michelson, which is a statically typed stack-based language for writing smart contracts that are executed on the blockchain platform Tezos. Helmholtz is designed on top of our extension of Michelson’s type system with refinement types. Helmholtz takes a Michelson program annotated with a user-defined specification written in the form of a refinement type as input; it then typechecks the program against the specification based on the refinement type system, discharging the generated verification conditions with the SMT solver Z3. We briefly introduce our refinement type system for the core calculus Mini-Michelson of Michelson, which incorporates the characteristic features such as compound datatypes (e.g., lists and pairs), higher-order functions, and invocation of another contract. Helmholtz successfully verifies several practical Michelson programs, including one that transfers money to an account and that checks a digital signature.

Helmholtz: A Verifier for Tezos Smart Contracts Based on Refinement Types
Yuki Nishida
Hiromasa Saito
Ran Chen
Akira Kawata
Jun Furuse
Kohei Suenaga
Atsushi Igarashi
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