Blockchain Security

Smart contract vulnerabilities, attack vectors, audit practices, and security tools.

Overview

Blockchain security protects against attacks and vulnerabilities.

Common Vulnerabilities

Reentrancy Attack

// Vulnerable contract
contract Vulnerable {
    mapping(address => uint256) public balances;
    
    function withdraw() public {
        uint256 balance = balances[msg.sender];
        require(balance > 0);
        
        (bool success, ) = msg.sender.call{value: balance}("");
        require(success);
        
        balances[msg.sender] = 0;
    }
}

// Secure contract
contract Secure {
    mapping(address => uint256) public balances;
    
    function withdraw() public nonReentrant {
        uint256 balance = balances[msg.sender];
        require(balance > 0);
        
        balances[msg.sender] = 0;
        
        (bool success, ) = msg.sender.call{value: balance}("");
        require(success);
    }
}

Security Tools

Practice

Audit a smart contract and fix vulnerabilities.