This writeup is a runthrough of challenges at https://capturetheether.com/challenges/ built on the Ropsten testnet. I will go through each problem in four steps:
- The intention of the contract
- The flawed assumption
- The process of exploiting the vulnerability
- The potential patches
I'll provide examples of the code I wrote as needed. To save time, we'll skip into the Lotteries section, starting with Guess the secret number, as that's the first problem which truly required some thought.