Browser SNARK
A javascript library to generate SNARKs in a browser. Developers can use this library to quickly setup zk-proofs in their applications.
These zk-proofs can be submitted on chain. The proof verification also ensures that one proof is used exactly once on chain.
Installation
Next.js
npm install browser-snark
Add the following to your .babel.rc
{
"presets": [
[
"next/babel",
{
"preset-env": {
// "debug": true,
"targets": [
"last 2 Edge versions",
"last 2 Opera versions",
"last 2 Safari versions",
"last 2 Chrome versions",
"last 2 Firefox versions"
]
}
}
]
]
}
Add the following to your next.config.js
/** @type {import('next').NextConfig} */
const nextConfig = {
reactStrictMode: true,
webpack: function (config, options) {
if (!options.isServer) {
config.resolve.fallback.fs = false;
}
config.experiments = { asyncWebAssembly: true };
return config;
},
}
module.exports = nextConfig
Usage for SNARK Proofs
The following SNARK proofs can be generated and verified using this library
Preimage of Hash
You can prove that the user knows the preimage of a hash and verify it on a smart contract.
Smart Contract
Add the following interface to your contract
interface Verifier {
function verifyWithNonce(
uint[2] memory a,
uint[2][2] memory b,
uint[2] memory c,
uint[3] memory input
) external returns(bool);
}
In your constructor instantiate the verifier;
Verifier verifier;
constructor() {
verifier = Verifier(<CONTRACT ADDRESS>);
// refer below table fot the contract address depending on the chain
}
| Chain | address |
|---|---|
| Goerli | 0x9247fbEB6195dF258A701D5749dD21b4696c1C22 |
| Optimism Mainnet | 0x7BA977e10e6f0EB05f3D6f4C1AB44626258e1d83 |
| Polygon Mainnet | 0xa932B4b9eeE2B098766828aa6E0803820ad3a064 |
| Ethereum Mainnet | Coming soon... |
In your function where you want to execute some logic only if proof is valid you need to do 3 steps
- Add 4 new parameters to your function
uint[2] memory a, uint[2][2] memory b, uint[2] memory c, uint[3] memory input - On the top of this function add
require(verifier.verifyWithNonce(a,b,c, input), "Invalid proof"); - Verify that the proof was generated for the correct hash
For example
function yourFunction(uint yourParam1, uint yourParam2, uint[2] memory a, uint[2][2] memory b, uint[2] memory c, uint[3] memory input) public {
require(verifier.verifyWithNonce(a,b,c, input), "Invalid proof");
require(input[2] == EXPECTED_HASH, "Proof generated for wrong hash");
//... Your logic
}
Javascript
Import browser-snark and create an object
import {Preimage} from 'browser-snark'
...
preimage = new Preimage();
...
Generate poseidon hash
myHash = preimage.hash(value)
Generate proof
if(myHash == EXPECTED_HASH){
const proof = preimage.generateProof(value, EXPECTED_HASH);
//... submit proof
}
Submit transaction with proof
contractWithSigner.yourFunction(yourParam1, yourParam2, proof.a, proof.b, proof.c, proof.input)
For an example usage you can see the app/ directory.
Todo
- Generate nonce from msg.sender
