writeup.md

Challenge Solve Me

Aight warm up time.
All you gotta do is call the solve function.
You can do it!

Difficulty: beginner

The challenge gave the following attachment: SolveMe.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @title SolveMe
 * @author BlueAlder duc.tf
 */
contract SolveMe {
    bool public isSolved = false;

    function solveChallenge() external {
        isSolved = true;
    }
   
}

As we can see from the description of the challenge and the smart contract code, all we have to do is to call the function solveChallenge(). We can implement the function call in a python script with the library web3.py.

from web3 import Web3
import json

url = "RPC_URL_ENDPOINT_GIVEN"
provider = Web3(Web3.HTTPProvider(url))
print("Is connected? ", provider.isConnected())
privateKey = 'PRIVATE_KEY_GIVEN'
nonce = 0

with open("solveMe.json") as f:       #json file with the contract ABI
    solveMe_json = json.load(f)

solveMeContract = Web3.toChecksumAddress('SOLVE_ME_CONTRACT_ADDRESS')
solveMe = provider.eth.contract(address=solveMeContract, abi = solveMe_json)

transaction = solveMe.functions.solveChallenge().buildTransaction({
    'gas': 70000,
    'gasPrice': Web3.toWei(40, 'gwei'), 
    'nonce': nonce
})      
signed_txn = provider.eth.account.signTransaction(transaction, private_key=privateKey)
provider.eth.sendRawTransaction(signed_txn.rawTransaction)

print("Solved? ", solveMe.functions.isSolved().call())

Running the script we obtain the flag: DUCTF{muM_1_did_a_blonkchain!}