ethernaut

Ethernaut is a fun game to learn blockchain development in Solidity. It consists of 25 challenges that need to be solved. I used Brownie for local testing and deploying the contracts to the Rinkeby network. Other Solidity development frameworks one can use are Truffle or Hardhat.

Here are my solutions:

1. Fallback

• Call contribute() function with ether value > 0.001
• Call receive() function with ether value > 0: e.g. await contract.send(toWei("0.1", "ether"))
• Call withdraw()

2. Fallout

• There is a typo in the constructor. Just call the Fal1out() functions to become the owner

3. Coin Flip

• A 2nd contract (attacking contract) is used to run the logic from the actual flipping contract to predict the result and then calls the actual contract with the calculated result.

4. Telephone

• Know the difference between tx.origin and msg.sender: tx.origin refers to the address the transaction was initiated from while msg.sender is the address that invoked the function.
• Solution: Call changeOwner() from another contract.

5. Token

• The require statement in the transfer function is useless, as the left side (balances[msg.sender] - _value) of the operand is rendered as uint, which is always greater than 0.
• Solution: Call transfer with a value greater than 20.