Smart Contracts

You write smart contracts by extending the base class SmartContract:

class HelloWorld extends SmartContract {}

The constructor of a SmartContract is inherited from the base class and cannot be overriden.

The zkApp account address (a public key) is its only argument:

const zkAppKey = PrivateKey.random();
const zkAppAddress = PublicKey.fromPrivateKey(zkAppKey);

const zkApp = new HelloWorld(zkAppAddress);

zkApp Accounts

On Mina, there is no strong distinction between normal “user accounts” and “zkApp accounts”. A zkApp account:

• Is an account on the Mina blockchain where a zkApp smart contract is deployed.
• Has a verification key associated with it.

The verification key stored on the zkApp account can verify zero knowledge proofs generated with the smart contract. The verification key lives on-chain for a given zkApp account and is used by the Mina network to verify that a zero knowledge proof has met all constraints defined in the prover.

Try it out

Add the following Class definition:

class HelloWorld extends SmartContract {}

Declare a variable zkAppKey and generate a private key using the random method on the PrivateKey class:

const zkAppKey = PrivateKey.random();

Declare a variable zkAppAddress by deriving a public key from the private key using the fromPrivateKey method on the PublicKey class:

const zkAppAddress = PublicKey.fromPrivateKey(zkAppKey);

Declare a variable zkApp and instantiate the HelloWorld class, providing zkAppAddress as an input parameter.

const zkApp = new HelloWorld(zkAppAddress);

Log our instantiated HelloWorld class:

Provable.log(zkApp)

Build and run the script in the terminal:

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

This will log/show our instantiated (empty) HelloWorld Smart Contract:

<ref *1> HelloWorld {
  sender: {
    self: [Circular *1],
    getUnconstrained: [Function: getUnconstrained],
    getUnconstrainedV2: [Function: getUnconstrainedV2],
    getAndRequireSignature: [Function: getAndRequireSignature],
    getAndRequireSignatureV2: [Function: getAndRequireSignatureV2]
  },
  events: {},
  address: PublicKey {
    x: Field { value: [Array] },
    isOdd: Bool { value: [Array] }
  },
  tokenId: Field { value: [ 0, [Array] ] }
}```