Circom Flutter

circom_flutter is a Flutter package for generating and verifying Circom zero-knowledge proofs using the groth16 backend.

The Swift bindings are generated by the mopro CLI using the Circom adapter, which utilizes circom-prover with circom-witnesscalc for witness generation and arkworks for groth16 proof construction.

To learn more about the original Rust implementation before generating bindings, please refer to zkmopro documentation.

Note

To use circom-witnesscalc, follow the README instructions to generate the graph file from your Circom circuits. Or the script from semaphore-rs

How to Import the Package

Adding a package dependency to an app

1. Manual Edit (Required for local path or specific Git dependencies): Open your pubspec.yaml file and add circom_flutter under dependencies.

     ```yaml
     dependencies:
         flutter:
             sdk: flutter
   
         circom_flutter:
             git:
                 url: https://github.com/zkmopro/circom_flutter
         # Or
         # circom_flutter:
         #    path: ../circom_flutter
     ```
   

2. Update Circuit Asset: Include your compiled Circom circuit .zkey and .bin file as an asset. Add the asset path to your pubspec.yaml under the flutter: section:

   flutter:
       uses-material-design: true # Ensure this is present
       assets:
           # Add the directory containing your circom circuit file(s)
           - assets/....zkey
           - assets/....bin
           # Or specify the file directly:
           # - assets/multiplier2_final.zkey

   Make sure the path points correctly to where you've placed your .zkey and .bin file within your Flutter project.

3. Install Package: Run the following command in your terminal from the root of your Flutter project:

   flutter pub get

How to Use the Package

Import the package

import 'package:circom_flutter/src/rust/third_party/circom_prover_bindings.dart';
import 'package:circom_flutter/src/rust/frb_generated.dart';

Update the main function to initialize the Rust library before running the app:

void main() async {
  await RustLib.init();
  runApp(const MyApp());
}

Load graph and zkey

Please checkout circom and circom-witensscalc to see how to generate the zkey and the graph.

final zkeyPath = await copyAssetToFileSystem(
      'assets/multiplier2_final.zkey');
final graphPath = await copyAssetToFileSystem(
      'assets/multiplier2.bin');

Note

To learn how to read a file from an app, please refer to the copyAssetToFileSystem function in the Flutter app.

circomProve

var inputs = '{"a":["3"],"b":["5"]}';

final proof = await circomProve(
    graphPath: graphPath,
    inputs: inputs,
    zkeyPath: zkeyPath,
);

verifyCircomProof

final isValid = await verifyCircomProof(
    zkeyPath: zkeyPath,
    proofResult: proof,
    proofLib: ProofLib.arkworks,
);

How to Build the Package

1. Use mopro-cli and choose circom

mopro init

choose circom

Update the circom-prover resource in Cargo.toml

circom-prover = { git = "https://github.com/zkmopro/mopro", branch = "circom-witnesscalc-path", features = [
    "circom-witnesscalc",
] }

and run

mopro build

choose flutter.

Flutter Example App

• Open the example app that uses the defined flutter package in the example/ folder

  cd example

• Install the dependencies

  flutter pub get

• Open an iOS simulator/device or an Android emulator/device and run the example app

  flutter run

• Clean the cache if you update the bindings and it throws errors

  flutter clean

![WARNING] Bindings generated by the mopro CLI use local crate paths by default, which makes them non-reproducible on other devices. To make the build reproducible, publish your Rust crate and reference it via a Git source instead of a local path at here. If you’d like to help address this limitation, contributions are welcome — see zkmopro/mopro#647 .

Community

• X account:
• Telegram group:

Acknowledgements

This work was initially sponsored by a joint grant from PSE and 0xPARC. It is currently incubated by PSE.