In Feb. this year, I and some other Balsn members participated in Paradigm CTF, an Ethereum-focused security competition held by Paradigm. First of all, thanks to the organizers for preparing such high-quality and impressive challenges! Luckily, our team, whoami, got fourth place with 11 out of 17 challenges solved.

List of members and solved challenges

When browsing the official repository, I noticed a clever trick used in a coding challenge, REVER, and wondered whether I could improve the solution furthermore. Here, I will share the optimal solution I can develop and some tips for EVM bytecode golfing.

Challenge

For Balsn CTF 2020 online, I also created two smart-contract challenges, Election and IdleGame. The source files of them are available on GitHub - x9453/my-ctf-challenges. Here is a walkthrough of the challenge IdleGame.

Thinking about making money by playing games? Try the first idle game on the blockchain!

• Type: Smart contract
• Solves: 4/490
• Keywords: Continuous token, Flash-mintable token, Arbitrage, DeFi attack

Challenge

For Balsn CTF 2020 online, I also created two smart-contract challenges, Election and IdleGame. The source files of them are available on GitHub - x9453/my-ctf-challenges. Here is a walkthrough of the challenge Election.

Balsn is holding the first Shaman King election. Who will be the winner?

• Type: Smart contract
• Solves: 5/490
• Keywords: ERC223, Reentrancy, ABI encoding, Integer overflow

Glad to participate in the on-site finals of Real World CTF in Beijing! Here I would like to share the solution to the challenges I solved.

Challenge

Bank is one of my two smart contract challenges for Balsn CTF 2019. You may find the source files here.

Again, as those ctfs did in the past, we also implemented our 100% secure bank system, but on blockchain this time.

• Type: Smart contract
• Solves: 1/720
• Keywords: Solidity 0.4, Uninitialized storage pointer, EVM storage layout