Transactions on blockchains are governed by smart contracts, which are often written in high-level languages but executed in bytecode. For the sake of transparency and reliability, it’s important that smart contracts be verified. With the growing value of digital assets being exchanged on the blockchain, the need for smart contract verification is amplified.
In this article, we’ll review what smart contracts are, why verification matters, and some of the most popular tools for verifying your smart contract. We’ll begin with a few basics for the newbies–feel free to skip to our list of best-in-class tools if you’ve been writing smart contracts for a while.
What are smart contracts?
Smart contracts are programs stored on a blockchain that execute when specific conditions are met. They run automatically when their conditions occur, without human monitoring or action. Smart contracts eliminate the need for intermediaries and enable peer-to-peer transactions.
But programs are only as good as their programming–and issues can arise as a smart contract’s source code is compiled into an executable.
What is smart contract verification?
Smart contracts are typically compiled before they can execute on a blockchain. Smart contract verification is the process of ensuring that a contract’s source code matches its bytecode.
Smart contracts are usually written in a high-level language such as Solidity, Vyper, or Rust. The source code is then compiled into bytecode for a virtual machine such as the Ethereum Virtual Machine (EVM).
This process raises a potential vulnerability. Once a smart contract is running on a blockchain, the only code on-chain is the bytecode, which is difficult for humans to read and understand. One would prefer to inspect the high-level source code. But how can one be sure that the source code and bytecode match? Smart contract verification serves to guarantee that match.
The primary responsibility for smart contract verification lies with the developers who create the smart contract. After all, the developers are the creators of the source code, which is needed for verification. This process is usually performed in conjunction with deployment to the blockchain.
However, that doesn't mean that sophisticated users or other developers can't verify contracts themselves. In fact, it is a good practice for a developer planning to interact with another contract in their own contract to verify it. Similarly, a user planning to interact with a contract in a way that could involve significant sums of money might also want to verify the contract. Third-party entities like blockchain security companies, auditing firms, or other entities who perform contract audits will also typically verify the contract as part of their auditing process.
While the primary responsibility lies with the contract's creator, anyone planning to interact with a contract in a significant way could perform verification themselves.
Why does smart contract verification matter?
It’s critical that smart contracts operate as expected, without bugs or security flaws that could allow an attacker to exploit it. If smart contracts don’t operate as expected, crypto can be stolen.
Why does bytecode sometimes fail to match its source code? It’s often a versioning problem–if there have been multiple versions of the source code, an older version might be inadvertently compiled that won’t match the current code. Changes to such areas as the code’s comments or documentation should be taken into account in the compiling process, but can cause glitches.
A public process
Smart contract verification is usually a public process, with both the smart contract code and its verification published for anyone to inspect. Transparency builds trust and helps your team acquire a reputation for reliability and precision. Published source code also means more eyes on your contract, which helps identify issues and possible improvements. Making your code available helps spur broader adoption of your smart contract.
Popular tools for smart contract verification
Smart contract verification is performed using automated tools. The tools available for verification depend on the blockchain and programming language you’re using. We’ll take a brief look at some of the more popular tools for Ethereum. Several of them are dependent on Etherscan, which is one of the oldest and most widely used tools for verification.
Ethereum-based smart contract testing and development platform Brownie is a top pick for Python developers. It supports smart contract verification for Solidity and Vyper on all networks supported by Etherscan. In addition, it has a simple interface and debugging tools. Property-based testing allows developers to create tests that describe a range of possible scenarios, rather than having to hand-write each test.
A trusted tool for exploring the Ethereum blockchain, Etherscan allows users to browse all of Ethereum’s public data, including smart contracts. Etherscan allows users to track their own transactions and wallet activity, but it’s also a popular analytics platform for smart contract verification. The block explorer’s uses include determining if a smart contract has a security audit and verified source code.
An Ethereum-based smart-contract development tool suite, Foundry is one-stop shopping for developing, testing, verifying, and deploying smart contracts in Solidity. Its CLI tool, Forge, can verify contracts on Etherscan, Sourcify, and other platforms.
Considered a convenient way to develop and test Ethereum and EVM-compatible smart contracts, Remix works with an Etherscan plug-in for contract verification. It’s open-source and browser based. You just supply three values to start testing: the contract to verify, constructor arguments, and the smart contract’s address on the blockchain.
Sourcify focuses on smart contract verification of Solidity, with a goal of enabling “transparent and human-readable smart contract interactions.” It’s an open-source, decentralized environment, and all contracts verified on its platform are publicly readable. Hardhat and Remix.IDE plugins can be used here, too.
Tenderly is a development and testing platform that can perform smart contract verification either with the Hardhat plugin or from the Tenderly dashboard.
Smart contract verification helps build a safer web3
We’ve seen why smart contract verification is necessary. It guarantees the authenticity, transparency, and trustworthiness of your smart contracts. By verifying your contracts, you're ensuring that the code governing transactions or other complex operations is exactly as stated, offering users a layer of assurance and fostering a climate of trust. Moreover, it underscores your commitment to transparency, and allows for more robust community interaction. As we continue to embrace the decentralized ethos of blockchain technology, let's also commit to the practices, like smart contract verification, that keep our systems secure, transparent, and trustworthy.