Code On Chain with Mina

Built as part of the Zk App Builders Program.

Original Vision

CodeOnChain

Learn mina blockchain development by building tiny apps that teach you key concepts. The user has to answer quizzes which are verified by a smart contract. At the end of each module, the users are expected to deploy a smart contract that demonstrates the concepts that they have learnt. (this was not implemented in the end) CodeOnChain's mina smart contract tests their smart contract by interacting with methods to see if the desired outcome is achieved and if possible, also verifies key lines of code. (this was not implemented in the end)

Actual Product

YK Proofs

A quiz web app that lets users globally prove their knowledge without revealing their knowledge by using ZK Proofs on the Mina Blockchain and they can also receive tokens that represent their knowledge. Even though the quiz transactions are public, the users' answers are not leaked so that all users have a fair chance and integrity is maintained.

Current Deployed Smart Contract: https://berkeley.minaexplorer.com/wallet/B62qkFzjHYDXq5qnFL7Q3Z63H94vUVPprA6HVULkW8rGtowLDeRusEz

How to Run

Running from Terminal

cd quiz-app

npm install (if running for the first time)

Running on Local Mina Node (All features)

npm run build && node build/src/main.js

Running on Berkeley (Only Quiz Feature works)

npm run build && node build/src/mainYKBerkeley.js

Running with Front end

(only the quiz app features) You can visit it on github pages https://alysiahuggins.github.io/code-on-chain-with-mina/

OR via the Terminal

cd quiz-app-ui

cd contracts

npm install (if running for the first time)

npm run build

cd ../ui/

npm install (if running for the first time)

npm run dev

How to Deploy

Running with Consolidated Contract

• To make deployment to berkeley easier (one address for all smart contract functionality), I created a file called contracts/YKProof.ts which includes all the smart contract functionality required. I use this when testing my deployment to berkeley. To test, I use the file, YKProofMain.ts and then follow the Mina instructions on how to deploy. https://docs.minaprotocol.com/zkapps/how-to-deploy-a-zkapp

Notes

Features

• Quiz (works on Local, Berkeley Testnet)
• Token Minting & sending (works on Local)
• Claim Accounts (works on Local, not yet tested on Berkeley)
• Leaderboard (not implemented yet)
• Single Transaction per Quiz Module i.e. Recursive Proofs (not implemented yet)

Features implemented in terminal

• Quiz (works on Local, Berkeley Testnet)
• Token Minting & sending (works on Local)
• Claim Accounts (works on Local, not yet tested on Berkeley)

Features implemented in frontend

Todo

• token minting
• user accounts
• token claims

Proposed Curriculum

• Mina Theory
• ZK Theory
• zkApp Theory
• Mina vs Ethereum
• zkApp Deployment & State Management
• zkApp Example Apps

Ideas About Implementaiton

• Think of it like a Mina Developer Roadmap. During each stage, you learn, answer quizzes and the boss stage is sending your smart contract to be verified by the Mina app. A high score is recorded, the more you retry each stage, the lower your score.

• There are many courses online that teach you about various blockchains but how do we know that people are actually learning. Quizzes are a great way to test someones knowledge. The app should be created in such as way where any course can be added, with questions and answers so that users can prove that they completed the course. this also makes it easy to add content to the course so that it's not locked to the platform. The purpose of Mina here could be to verify identity but more importantly, to verify knowledge.

• • I want there to be a gamification aspect as well which I'm not sure is overkill. I'm thinking as simple as a crowssword puzzle or more animated with a flappy birds or matching bubbles implementation. The crossword puzzle can eventually be interactive which would be interesting with private inputs.

Implementation Steps

• Offchain questions and answers (DONE)

• Offchain questions and answers stored on chain with merkle trees (DONE)

• Valiate user response with a zkProof i.e. a Mina blockchain transaction (DONE)

• Claim1: Store Users Name and Password in a Merkle Tree so that they can claim their tokens (DONE)

• Claim2: Allow Users to supply their own Mina Address to claim tokens (IN PROGRESS)

• Validate user responses with recursive zkProofs (One blockchain transaction per module) (IN PROGRESS)

• Reward user with token at the end of each module (IN PROGRESS)

• Implement Modules (entry to learning then quiz section) (IN PROGRESS)

• Offchain leaderboard stored on chain with merkle trees (NOT STARTED)

• Validate smart contract code with a test suite in the client (NOT STARTED)

• Add Tests (NOT STARTED)

• Retrieve questions & answers from IPFS for merkle tree (NOT STARTED)

• Learn how to communicate with another deployed smart contract from within my Quiz Smart Contract (NOT STARTED)

Questions for Mina Team

• The user can only progress if they get all questions correct in each module. Should the quiz responses be stored as state variables and verified by smart contracts? Or is it ok to be stored offchain and verified on the client?
• How do I call a method from another smart contract
• Where do I store the answers to the questions so that they stay private?
• can I create a token with SnarkyJS?
• How can you set the merkleRoot hash? e.g. smartcontract deployed and you want to set the Root of your client code as the same that's on the blockchain ledger

Concepts

Token Claims

When the user completes the quiz and got all the questions correctly, QuizTokens are minted to an address that we control. Users can claim these tokens to their address when they want, in the meanwhile, the user's username and password is stored in a merkletree.

Gotcha's

Verification Keys

If the verification key is different that the deployed smart contract verification, make sure you are using the same snarkyjs version in package.json. Your verification keys are different (the one in your client app vs what's deployed on Mina) when you try to send a transaction with Auro wallet and get the error Couldn't send zkApp command: verification_failed invalid_proof. See details on Mina's discord here https://discord.com/channels/484437221055922177/1047268822530392084

Errors and Workarounds

Stackoverflow

• When I tried to compile a Merkle Tree of size 1000

invalid fee excess

deploy tokenZkApp
Error: Invalid fee excess.
This means that balance changes in your transaction do not sum up to the amount of fees needed.
Here's the list of balance changes:

Account update #1) -101.00 MINA
Account update #2) 10.00 MINA

Total change: -91.00 MINA

what caused it: i used the same zkAppAddress in the deploy args for more than one smart contract solution: use different zkAppAddress in deploy args for various smart contracts

Error: Transaction verification failed: Cannot update field 'incrementNonce' because permission for this field is 'Signature', but the required authorization was not provided or is invalid.

You are using a different address

problem: signing a transaction with the key that did not do the deployment, instead sign with that key or just do tx.prove()

Error: Transaction verification failed: Cannot update field 'incrementNonce' because permission for this field is 'Signature', but the required authorization was not provided or is invalid.

solution: incorrect key used for signing, used the same key that deployed the smart contract

Testnet Address

Berkeley3 B62qkFzjHYDXq5qnFL7Q3Z63H94vUVPprA6HVULkW8rGtowLDeRusEz

Unsolved Issues

Error: getAccount: Could not find account for public key B62qkFzjHYDXq5qnFL7Q3Z63H94vUVPprA6HVULkW8rGtowLDeRusEz with the tokenId wUH3Pg4vmt4n8mMDm5SLHYDQFjVNyiRtTqzgmUK392rYScHgPj

• can't send tokens to an account unless the tokendeploy method has been called so that it's made a token account