基于区块链用代码实现一个完整的身份认证系统

一个完整的身份认证系统需要包括用户注册、登录、身份验证、权限管理等功能。下面是一个基于区块链的完整身份认证系统的代码实现：

1. 定义数据结构

struct User {
    address userAddress; // 用户地址
    bytes32 passwordHash; // 密码哈希
    bytes32 identityHash; // 身份哈希
}

mapping(string => User) users; // 用户映射表

mapping(string => mapping(string => uint8)) permissions; // 权限映射表

2. 用户注册

function register(string memory username, string memory password, string memory identity) public {
    require(users[username].userAddress == address(0), "User already exists");
    address userAddress = msg.sender;
    bytes32 passwordHash = keccak256(bytes(password));
    bytes32 identityHash = keccak256(bytes(identity));
    users[username] = User(userAddress, passwordHash, identityHash);
}

3. 用户登录

function login(string memory username, string memory password) public view returns (bool) {
    User storage user = users[username];
    bytes32 passwordHash = keccak256(bytes(password));
    return user.userAddress == msg.sender && user.passwordHash == passwordHash;
}

4. 用户信息修改

function updateUserInfo(string memory username, string memory newUsername, string memory newPassword, string memory newIdentity) public {
    require(users[username].userAddress == msg.sender, "Not authorized");
    bytes32 passwordHash = keccak256(bytes(newPassword));
    bytes32 identityHash = keccak256(bytes(newIdentity));
    users[newUsername] = User(msg.sender, passwordHash, identityHash);
    delete users[username];
}

5. 身份验证

function verifyIdentity(string memory username, string memory identity) public view returns (bool) {
    User storage user = users[username];
    bytes32 identityHash = keccak256(bytes(identity));
    return user.userAddress == msg.sender && user.identityHash == identityHash;
}

6. 权限管理

function grantPermission(string memory username, string memory resource, uint8 permission) public {
    require(users[username].userAddress == msg.sender, "Not authorized");
    permissions[username][resource] = permission;
}

function checkPermission(string memory username, string memory resource, uint8 permission) public view returns (bool) {
    return permissions[username][resource] >= permission;
}

需要注意的是，以上代码只是一个简单的示例，实际的身份认证系统需要考虑更多的安全性和可扩展性问题，如防止重放攻击、防止恶意用户注册等。同时，还需要将代码部署在区块链上，确保数据的安全性和不可篡改性。