solidity-security

# 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 ```javascript // 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 ```solidity 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"); } } ```