# Smart Contracts
Smart contracts on Nibiru are written in Rust CosmWasm, which runs in the WebAssembly (Wasm) runtime. CosmWasm smart contracts are impervious to re-entrancy attacks, the most common smart contract vulnerabilies in Ethereum, are designed to be portable across IBC chains, and offer the memory safety and performance of Rust.
# Why CosmWasm Stands Out
CosmWasm offers a compelling set of features and advantages for smart contract developers and users of Nibiru. Here's a closer look at some of these benefits and why we love CosmWasm:
Security: Defence against re-entrancy, denial of service attacks related to excessive gas consumption, and compile-time checks for overflow/underflow issues help make CosmWasm the ideal framework for developing secure, production-ready smart contracts.
Memory Safety: CosmWasm contracts run in a sandboxed environment, ensuring that they can't harm the host system or access unintended data. The use of Rust, a memory-safe language, further enhances the security of contracts.
Performance: Leveraging the efficiency of WebAssembly, CosmWasm can achieve near-native execution speeds for smart contracts, resulting in faster transaction processing. Here, "near-native execution" contracts the performance of Wasm with the performance of code that runs directly on the hardware without any intermediate layers (native code). This is possible because Wasm code is low-level bytecoe that gets compiled nad optimized for the host machine before execution.
Modularity and Flexibility: CosmWasm is designed to be modular, allowing chains to adopt it without mandating its use for all smart contracts on the chain. CosmWasm is not just a layer on top of the Cosmos-SDK; it's deeply integrated, allowing for advanced features and tight interaction with the underlying blockchain infrastructure.
Interoperability: CosmWasm contracts can execute cross-chain logic with the Inter-Blockchain Communication (IBC) protocol, enabling contracts to interoperate with other IBC-enabled chains.
Upgradable Contracts: CosmWasm supports contract migration, allowing developers to upgrade their contracts post-deployment, a feature which many traditional smart contract platforms lack.
# Avoiding Reentrancy Attacks
CosmWasm smart contracts avoid all reentrancy attacks by design. This point deserves an article by itself, but in short, a large class of exploits in Ethereum is based on this trick (opens new window) .
The idea is that in the middle of the execution of a function on Contract A, it calls a second contract (explicitly or implicitly via send). This transfers control to contract B, which can now execute code, and call into Contract A again. Now there are two copies of Contract A running, and unless you are very, very careful about managing the state before executing any remote contract or make very strict gas limits in sub-calls, this can trigger undefined behavior in Contract A and a clever hacker can reentrancy this as a basis for exploits, such as the DAO hack.
Cosmwasm avoids this completely by preventing any contract from calling another one directly. Clearly, we want to allow composition, but inline function calls to malicious code create a security nightmare. The approach taken with CosmWasm is to allow any contract to return a list of messages to be executed in the same transaction.
This means that a contract can request a send to happen after it is finished (eg. release escrow), or call into another contract. If the future messages fail, then the entire transaction reverts, including updates to the contract's state. This allows for atomic composition and quite a few security guarantees, with the only real downside that you cannot view the results of executing another contract, rather you can just do "revert on error".
# Lessons Learned from Ethereum
Ethereum is the grandfather of all blockchain smart contract platforms and has far more usage and real-world experience than any other platform. We cannot discount this knowledge but instead learn from their successes and failures to produce a more robust smart contract platform.
They have compiled a list of all known Ethereum attack vectors (opens new window) along with mitigation strategies. We shall compare Cosmwasm against this list to see how much of this applies here. Many of these attack vectors are closed by design. A number remain and a section is planned on avoiding the remaining such issues.