Remix Public Challenge #4

# Remix Public Challenge #4 ## About ### Remix Challenges is an onchain quiz that uses a ZK Proof. People submitting answers won't reveal their solutions. **When the questions have been correctly answered, a Remixer badge can be minted.** - Why not just code the challenge in Solidity? All the data in the Ethereum blockchain is public and visible. This means that if the challenge is coded in Solidity, the first user who finds the solution will submit that solution in **a transaction** and thus the solution will be visible by everyone. Using a ZK Proof, we only require the user to post a **proof** that the challenge has been successfully completed. - Is it possible to double post the same proof? There are 2 parts to this question - can the same person (address) post the same proof? And can a different address post the same proof? Incorporated in the proof is a special parameter named `nullifier` - a number that a user chooses and inputs when generating the proof. Inputting a different nullifier with the correct answers will generate a different proof. If a user correctly answers the questions and uses "142 as the nullifier when generating the proof, the smart contract will remember that the nullifier `142` has been used. If another number is used, the proof will be different but will still show that the questions were correctly answered. So even when the actual proof becomes public, it won't be possible to re-post that specific proof. An address (a user) can only submit a single proof - even if another `nullifier` is used. And a `nullifier` can only be used once. - If a user knows how to complete a challenge, can he compute with another salt and win the game again? The contract keeps a mapping of all the users that completed the challenge (using `msg.sender`), it is also possible to ask for a signed nullifier instead of directly using `msg.sender` ## Cost The contract for Remix Challenge is on the Optimism chain and posting the proof will cost about 65 cents worth of Optimism ETH in gas. ## Setup - Clone the following repository in Remix `https://github.com/yann300/remix-challenges`. - In Remix, to find the **clone** option, go to the hamburger menu at the top of the File Explorer. - Once the cloned repo has been retrieved, open the file, **compute.ts**, which is in the **scripts** folder. ## Updating the Nullifier - On line 54 of compute.ts, choose a random number for the nullifier. Replace the example nullifier. ## The Questions of Remix Public Challenge #4 1. How do you create a workspace that uses the NFT template? **A:** In the File Explorer, click the **+** button next to the **WORKSPACES** title. Then in the modal, Select ERC20. **B:** In the File Explorer, click the **+** button next to the **WORKSPACES** title. Then in the modal, Select ERC721. **C:** On the home tab, click on the **New File** button. 2. In Remix, when setting up an NFT template in the Create Workspace modal, there are a number of checkboxes in the **Features** section. If you only check **Mintable**, what is the only function that that you see in your solidity file (besides the constructor)? **A:** safeMint **B:** approve **C:** transferFrom 3. In Remix's Deploy & Run module, AtAddress used is to access & to interact with a deployed contract. In order to use AtAddress, you'll either need the deployed contract's ABI or its source code compiled to the same version of Solidity and you'll need: **A:** Approval from the contract's owner **B:** The contract's address **C:** The contract's verification status. 4. Why did the community create token standards? **A:** So that the community can control and approve the tokens that are created. **B:** In order to restrict the functionality of tokens to safe and non-malicious actions. **C:** So that the community can create tokens that are interoperable with other contracts, products, and services. Input only the letter (A, B, or C) of the corresponding correct answer. ## Answering the questions - Starting on line 56 of compute.ts, input the answers to the questions. - In the case of multiple choice questions, only input the letter (A, B, or C) of the corresponding correct answer. - Run the script by either right-clicking on the script in the File Explorer or clicking on the green play button. - If the program executes correctly, you have successfully answered the 4 questions. - In Remix's terminal, you'll see a log of the proof. The script will save this proof in a file in the folder named **generated**. - **If you have not answered the questions correctly**, the proof will NOT be generated and the file `generated/proof.json` will not be created. - This proof can be used in a **verifier** to prove that you found the 4 values. By doing so, only the proof needs to be shared, you don't need to share the 4 values, but everyone can be certain that you know these values. - Go to the next steps. ## Mint a Remixer Badge using the generated proof - Switch to the Optimism network. Make sure that in the Deploy & Run plugin, you are connected to Optimism and that your browser wallet (often MetaMask) is also connected there and that you have enough ETH to pay for the minting (usually about 40 cents). - Open the file scripts/publish-solution.ts. - This script will use the proof generated in the previous section `generated/proof.json` for calling the function `publishChallenge` in the Remix Rewards contract. - Run the transaction for publishing the solution. - Once the solution has been published head to https://rewards.remix.ethereum.eth.limo to see the newly created badge.