SKILL.md
Solidity Security
Master smart contract security best practices, vulnerability prevention, and secure Solidity development patterns.
When to Use This Skill
- Writing secure smart contracts
- Auditing existing contracts for vulnerabilities
- Implementing secure DeFi protocols
- Preventing reentrancy, overflow, and access control issues
- Optimizing gas usage while maintaining security
- Preparing contracts for professional audits
- Understanding common attack vectors
Detailed patterns and worked examples
Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.
Testing for Security
// Hardhat test example
const { expect } = require("chai");
const { ethers } = require("hardhat");
describe("Security Tests", function () {
it("Should prevent reentrancy attack", async function () {
const [attacker] = await ethers.getSigners();
const VictimBank = await ethers.getContractFactory("SecureBank");
const bank = await VictimBank.deploy();
const Attacker = await ethers.getContractFactory("ReentrancyAttacker");
const attackerContract = await Attacker.deploy(bank.address);
// Deposit funds
await bank.deposit({ value: ethers.utils.parseEther("10") });
// Attempt reentrancy attack
await expect(
attackerContract.attack({ value: ethers.utils.parseEther("1") }),
).to.be.revertedWith("ReentrancyGuard: reentrant call");
});
it("Should prevent integer overflow", async function () {
const Token = await ethers.getContractFactory("SecureToken");
const token = await Token.deploy();
// Attempt overflow
await expect(token.transfer(attacker.address, ethers.constants.MaxUint256))
.to.be.reverted;
});
it("Should enforce access control", async function () {
const [owner, attacker] = await ethers.getSigners();
const Contract = await ethers.getContractFactory("SecureContract");
const contract = await Contract.deploy();
// Attempt unauthorized withdrawal
await expect(contract.connect(attacker).withdraw(100)).to.be.revertedWith(
"Ownable: caller is not the owner",
);
});
});Audit Preparation
contract WellDocumentedContract {
/**
* @title Well Documented Contract
* @dev Example of proper documentation for audits
* @notice This contract handles user deposits and withdrawals
*/
/// @notice Mapping of user balances
mapping(address => uint256) public balances;
/**
* @dev Deposits ETH into the contract
* @notice Anyone can deposit funds
*/
function deposit() public payable {
require(msg.value > 0, "Must send ETH");
balances[msg.sender] += msg.value;
}
/**
* @dev Withdraws user's balance
* @notice Follows CEI pattern to prevent reentrancy
* @param amount Amount to withdraw in wei
*/
function withdraw(uint256 amount) public {
// CHECKS
require(amount <= balances[msg.sender], "Insufficient balance");
// EFFECTS
balances[msg.sender] -= amount;
// INTERACTIONS
(bool success, ) = msg.sender.call{value: amount}("");
require(success, "Transfer failed");
}
}