WASM and Rust: The Killer Smart Contract Combo?

August 14, 2023

WASM and Rust: The killer smart contract combo?

In the evolving landscape of blockchain technology, smart contracts have become a cornerstone for decentralized applications (dApps). Traditionally, Ethereum's Solidity has dominated this space, but the advent of WebAssembly (WASM) and the Rust programming language is set to disrupt the smart contract arena.

The origin of WASM

WebAssembly, or WASM for short, is an open standard that defines a portable binary code format for executable programs. Think of it as a 'universal language' that different types of computers can understand, enabling software to run faster and more efficiently on any device. Its primary goal is to enable high-performance applications on web pages, but it does not limit itself to just web-based applications. Modern blockchains such as Cosmos and Polkadot have recognized the potential of WASM and are already employing it in their ecosystems.

WebAssembly is platform-independent, meaning it can run on any operating system, and is compatible with most programming languages. This flexibility opens up new possibilities for smart contract development, which have been often confined to domain-specific languages like Solidity on the Ethereum Virtual Machine (EVM) or Move on Aptos and Sui.

Rust: The New Standard for Smart Contract Development?

Rust has found a natural home in the WASM environment. As WASM-compatible sidechains often use Rust for reference implementations, it provides a lower entry barrier for developers compared to domain-specific languages. This choice allows developers to leverage a wide range of libraries that are applicable beyond blockchain-specific needs, thereby enhancing the versatility and applicability of their projects.

Notably, several cryptocurrency projects have already recognized and leveraged the benefits of WASM. A very interesting example is that of CosmWasm - an open-source project which allows developers to write smart contracts in Rust, and then compile them to WASM for execution on the Cosmos blockchain. This not only offers a safer execution environment thanks to qualities of Rust but also provides an excellent framework that minimizes the ability to tamper with the blockchain message and hence reduces the attack surface massively.

Advantages of Rust over Solidity

One of the most compelling benefits of Rust is its native compile capability, which does away with the need for a virtual machine to run the testing suite. This results in a more flexible unit testing approach and significantly faster test execution.

Rust's testing ecosystem also benefits from the abundance of testing tools available. For instance, proptest is a property testing framework that enables developers to automate the process of finding edge cases. Additionally, Rust's compatibility with tools not specifically designed for it, such as KLEE, a symbolic execution engine, allows developers to leverage symbolic execution to enhance the security of their smart contracts even further. Symbolic execution is a sophisticated testing approach where, instead of using actual input values, the software is tested with symbolic values to identify potential issues in all possible execution paths.

A Wide range of tools have already been developed for Rust and LLVM and as such a smart contract developer or an auditor can easily apply them in blockchain applications. The technological evolution of Rust and its ecosystem is not limited by the progress of a specific blockchain.   

Unleashing the Power of Fuzz Testing

Another powerful testing method that Rust facilitates is fuzzing - a process where random and malformed inputs are fed into a program to uncover potential errors or vulnerabilities. Fuzzing in Rust can lead to the discovery of hidden or unlikely errors in smart contract code that might have been overlooked during standard testing processes. In the context of blockchain, where contracts are immutable once deployed and any bug can be potentially catastrophic, fuzz testing provides an added layer of security by helping developers catch and fix issues before they reach production.

It is worth noting that the EVM’s development environment has matured and many tools, including fuzz testing are available. One example could be A16Z’s halmos (https://github.com/a16z/halmos) which offers both fuzzing and symbolic execution capabilities.

Flexibility in Programming Paradigm

Rust does not impose a specific programming paradigm, offering flexibility that Solidity often lacks. While Solidity enforces an object-oriented approach, Rust allows developers to choose the paradigm that best suits their project's needs. This flexibility can lead to more efficient and readable code, making it easier for teams to collaborate and iterate on their projects.

Such flexibility can be especially useful when building complex applications needing proper modularization and better control over storage access patterns. Moreover, recently cross-chain applications are becoming more and more common, and hence Rust may be better suited to handle different call conventions and cross-chain protocols. 


The fusion of WASM and Rust symbolizes a significant evolution in smart contract development. With pioneers like Cosmos and Polkadot leading the charge, it's evident that the future of smart contract development could very well be shaped by WASM.