> For the complete documentation index, see [llms.txt](https://ret2basic.gitbook.io/ctfwriteup/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ret2basic.gitbook.io/ctfwriteup/web3-ctf/ethernaut/gatekeeper-three.md).

# Gatekeeper Three

{% embed url="<https://ethernaut.openzeppelin.com/level/0x653239b3b3E67BC0ec1Df7835DA2d38761FfD882/>" %}
Ethernaut - Gatekeeper Three
{% endembed %}

## Objective

Cope with gates and become an entrant.

**Things that might help:**

* Recall return values of low-level functions.
* Be attentive with semantic.
* Refresh how storage works in Ethereum.

## Contract

```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SimpleTrick {
  GatekeeperThree public target;
  address public trick;
  uint private password = block.timestamp;

  constructor (address payable _target) {
    target = GatekeeperThree(_target);
  }
    
  function checkPassword(uint _password) public returns (bool) {
    if (_password == password) {
      return true;
    }
    password = block.timestamp;
    return false;
  }
    
  function trickInit() public {
    trick = address(this);
  }
    
  function trickyTrick() public {
    if (address(this) == msg.sender && address(this) != trick) {
      target.getAllowance(password);
    }
  }
}

contract GatekeeperThree {
  address public owner;
  address public entrant;
  bool public allowEntrance;

  SimpleTrick public trick;

  function construct0r() public {
      owner = msg.sender;
  }

  modifier gateOne() {
    require(msg.sender == owner);
    require(tx.origin != owner);
    _;
  }

  modifier gateTwo() {
    require(allowEntrance == true);
    _;
  }

  modifier gateThree() {
    if (address(this).balance > 0.001 ether && payable(owner).send(0.001 ether) == false) {
      _;
    }
  }

  function getAllowance(uint _password) public {
    if (trick.checkPassword(_password)) {
        allowEntrance = true;
    }
  }

  function createTrick() public {
    trick = new SimpleTrick(payable(address(this)));
    trick.trickInit();
  }

  function enter() public gateOne gateTwo gateThree {
    entrant = tx.origin;
  }

  receive () external payable {}
}
```

## Writeup