Zero-knowledge applications (zkApps) enable privacy-preserving decentralized apps on Mina Protocol. This tutorial uses O1js (formerly SnarkyJS), a TypeScript library for building zk-SNARK circuits, to create a simple zkApp.
Prerequisites
- Basic knowledge of TypeScript/JavaScript.
- Node.js (v18+ recommended).
- Familiarity with Mina Protocol concepts (e.g., zk-SNARKs).
- Terminal/CLI proficiency.
1. Environment Setup
Install Dependencies
CODE
npm install -g zkapp-cli # Mina zkApp CLI tool
npm install -g typescript ts-node # TypeScript tools
2. Initialize Project
Create a new zkApp project using the Mina CLI:
CODE
zk create my-zkapp --template simple # Use the "simple" template
cd my-zkapp
npm install
Project Structure
CODE
my-zkapp/
├── src/
│ ├── contracts/ # zkApp smart contracts
│ ├── tests/ # Test files
│ └── index.ts # Main entry (optional)
├── zkapp.config.json # Configuration
└── package.json
3. Write a zkApp Contract
Create src/contracts/NumberUpdate.ts:
CODE
import {
SmartContract,
State,
state,
method,
PublicKey,
PrivateKey,
} from 'o1js';
export class NumberUpdate extends SmartContract {
@state(Field) number = State<Field>(); // On-chain state
init() {
super.init();
this.number.set(Field(0)); // Initialize state
}
// Method to update the number with a constraint
@method updateNumber(newNumber: Field) {
const currentNumber = this.number.get();
this.number.assertEquals(currentNumber); // Verify current state
newNumber.assertLessThan(Field(100)); // Custom constraint: new number < 100
this.number.set(newNumber); // Update state
}
}
Key Concepts
@state: Declares on-chain state.
@method: Defines a zk-SNARK circuit (private computation).
Field: A primitive for finite field arithmetic.
4. Compile the Contract
Compile to generate proofs and AVM bytecode:
CODE
zk compile src/contracts/NumberUpdate.ts
- Compilation may take 2-10 minutes (generates zk-SNARK keys).
5. Write Tests
Create src/tests/NumberUpdate.test.ts:
CODE
import { Test, expect } from 'zken';
import { NumberUpdate } from '../contracts/NumberUpdate';
import { Field, PrivateKey } from 'o1js';
describe('NumberUpdate', () => {
let zkApp: NumberUpdate;
let deployer: PrivateKey;
beforeAll(async () => {
deployer = PrivateKey.random(); // Test account
});
beforeEach(() => {
zkApp = new NumberUpdate(deployer.toPublicKey());
});
it('updates number correctly', async () => {
await zkApp.compile(); // Ensure contract is compiled
// Deploy
const tx = await Mina.transaction(deployer, () => {
zkApp.deploy();
zkApp.updateNumber(Field(42)); // Update to 42
});
await tx.prove(); // Generate proof
await tx.sign([deployer]).send(); // Submit to testnet
// Verify on-chain state
expect(zkApp.number.get()).toEqual(Field(42));
});
});
Run tests:
CODE
zk test
6. Deploy to Mina Network
Configure Network
Update zkapp.config.json:
CODE
{
"networks": {
"berkeley": {
"url": "https://proxy.berkeley.minaexplorer.com/graphql",
"keyPath": "./keys/berkeley.json"
}
}
}
Fund Account & Deploy
- Get testnet MINA from
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