Description This challenge was in the Misc category. 1 2 3 4 5 6 7 8 9 While travelling to a conference in Paris, Herlock Sholmès sees a troubled police inspector. After asking him what was his problem, the inspector tells Herclock that he is trying to understand how two spies communicate with each other. Once every week both spies get on the Eiffel tower, but never get in speaking distance of each other.

Description The challenge provides the following contract, and, same as the Welcome challenge, the goal is to “unlock” to get the flag. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 pragma solidity ^0.7.1; contract hidden { bool public isLocked; bytes32 private key; bool private other; uint256 private garbage = 88888888888; uint256 public useless; uint256 private bob; constructor() { //hidden } function unlock(bytes32 _something) public { require(other); if (key == _something) { isLocked = false; } } } Solving the challenge Like in the previous challenge, to unlock, we need a key, except this time it is private:

Description The challenge provides the following contract, and the goal is to “unlock” to get the flag. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 pragma solidity ^0.7; contract welcome { bool public isLocked; string public key; constructor(string memory _key) { isLocked = true; _key = key; } function unlock(string memory _something) public { if (keccak256(abi.encodePacked(key)) == keccak256(abi.encodePacked(_something))) { isLocked = false; } } } Setup The CTF provided a very nice tutorial to setup the THCONETH network: