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2025 ETHTaipei Workshop

· 9 min read
Vivian Jeng
Vivian Jeng
Developer on the Mopro Team

Overview​

This tutorial guides developers through getting started with Mopro and building a native mobile app from scratch. It covers

info

This is a workshop tutorial from ETHTaipei 2025 in April. If you'd like to follow along and build a native mobile app, please check out this commit: 085fa41.

  • We also offer comprehensive iOS and Android tutorials to guide you through the entire process, ensuring you don’t miss anything!

    • iOS

    • Android

0. Prerequisites​

  • XCode or Android Studio
    • If you're using Android Studio, ensure that you follow the Android configuration steps and set the ANDROID_HOME environment variable.
  • Rust and CMake
info

Documentation: https://zkmopro.org/docs/prerequisites

1. Download Mopro CLI tool​

We offer a convenient command-line tool called mopro to streamline the development process. It functions similarly to tools like npx create-react-app or Foundry, enabling developers to get started quickly and efficiently.

git clone https://github.com/zkmopro/mopro
cd mopro/cli
cargo install --path .
cd ../..

2. Initialize a project with Mopro CLI​

The mopro init command helps you create a Rust project designed to generate bindings for both iOS and Android. This step is similar to running npx create-react-app, so select the directory where you want to create your new app.

mopro init

Start by selecting a name for your project (default: mopro-example-app).

Next, choose the proving system that best fits your needs—Mopro currently supports both circom and halo2. For this example, we’ll be using circom.

mopro init

Next, navigate to your project directory by running:

cd mopro-example-app

3. Build Rust bindings with mopro CLI​

mopro build command can help developers build binaries for mobile targets (e.g. iOS and Android devices).

mopro build

  • Choose debug for faster builds during development or release for optimized performance in production.

  • Select the platforms you want to build for: ios, android, web.

  • Select the architecture for each platform:

    • iOS:
ArchitectureDescriptionSuggested
aarch64-apple-iosFor physical iOS devices✅
aarch64-apple-ios-simFor M-series Mac simulators✅
x86_64-apple-iosFor Intel-based Mac simulators-
  • Android:
ArchitectureDescriptionSuggested
x86_64-linux-androidFor 64-bit Intel architecture (x86_64)✅
i686-linux-androidFor 32-bit Intel architecture (x86)-
armv7-linux-androideabiFor 32-bit ARM architecture (ARMv7-A)-
aarch64-linux-androidFor 64-bit ARM architecture (ARMv8-A)✅

mopro build

warning

The build process may take a few minutes to complete.

Next, you will see the following instructions displayed:

mopro-build-finish

4. Create templates for mobile development​

mopro create command generates templates for various platforms and integrates bindings into the specified directories.

mopro create

Currently supported platforms:

  • iOS (Xcode project)
  • Android (Android Studio project)
  • React Native
  • Flutter
  • Web

After running the mopro create command, a new folder will be created in the current directory, such as:

  • ios
  • android
  • react-native
  • flutter
  • web (currently does not support Circom prover)

You will then see the following instructions to open the project:

mopro-create

If you want to create multiple templates, simply run mopro create again and select a different framework each time.

mopro-create-android

5. Run the app on a device/simulator​

iOS​

Open the Xcode project by running the following command:

open ios/MoproApp.xcodeproj

Select the target device and run the project by pressing cmd + R.

Alternatively, you can watch this video to see how to run the app.

Android​

Open the Android Studio project by running the following command:

open android -a Android\ Studio

Run the project by pressing ^ + R or ctrl + R.

Alternatively, you can watch this video to see how to run the app.

6. Update circuits​

This section explains how to update circuits with alternative witness generators and corresponding zkey files. We use the Keccak256 circuit as a reference example here.

  1. Add wasm and zkey file in the test-vectors/circom folder

  2. In src/lib.rs file, update the circuit's witness generator function definition.

    -  rust_witness::witness!(multiplier2);
    +  rust_witness::witness!(keccak256256test);

    mopro_ffi::set_circom_circuits! {
    -    ("multiplier2_final.zkey", WitnessFn::RustWitness(multiplier2_witness))
    +    ("keccak256_256_test_final.zkey", WitnessFn::RustWitness(keccak256256test_witness))
    }
    warning

    The name should match the lowercase version of the WASM file, with all special characters removed.
    e.g.
    multiplier2 -> multiplier2
    keccak_256_256_main -> keccak256256main
    aadhaar-verifier -> aadhaarverifier

  3. Similar to Step 3, regenerate the bindings to reflect the updated circuit.

    mopro build

  4. Manually update the bindings in the app by replacing the existing ones.

    • iOS:

      • Replace ios/MoproiOSBindings with MoproiOSBindings.

    • Android:

      • Replace android/app/src/main/jniLibs with MoproAndroidBindings/jniLibs

      • Replace android/app/src/main/java/uniffi with MoproAndroidBindings/uniffi

    info

    We aim to provide the mopro update CLI tool to assist with updating bindings. Contributions to this effort are welcome.https://github.com/zkmopro/mopro/issues/269

  5. Copy zkeys to assets

    • iOS:
      Open Xcode, drag in the zkeys you plan to use for proving, then navigate to the project’s Build Phases. Under Copy Bundle Resources, add each zkey to ensure it's included in the app bundle.

      Alternatively, you can watch this video to see how to copy zkey in XCode.

    • Android
      Paste the zkey in the assets folder: android/app/src/main/assets.

      Alternatively, you can watch this video to see how to copy zkey in XCode.

  6. Update circuit input and zkey path

  • Update zkeyPath to keccak256_256_test_final

    • iOS:
    - private let zkeyPath = Bundle.main.path(forResource: "multiplier2_final", ofType: "zkey")!
    + private let zkeyPath = Bundle.main.path(forResource: "keccak256_256_test_final", ofType: "zkey")!
    • Android:
    - val zkeyPath = getFilePathFromAssets("multiplier2_final.zkey")
    + val zkeyPath = getFilePathFromAssets("keccak256_256_test_final.zkey")

  • Update circuit inputs: https://ci-keys.zkmopro.org/keccak256.json

    • iOS:
    - let input_str: String = "{\"b\":[\"5\"],\"a\":[\"3\"]}"
    + let input_str: String = "{\"in\":[\"0\",\"0\",\"1\",\"0\",\"1\",\"1\",\"1\",\"0\",\"1\",\"0\",\"1\",\"0\",\"0\",\"1\",\"1\",\"0\",\"1\",\"1\",\"0\",\"0\",\"1\",\"1\",\"1\",\"0\",\"0\",\"0\",\"1\",\"0\",\"1\",\"1\",\"1\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\"]}"
    • Android:
    - val input_str: String = "{\"b\":[\"5\"],\"a\":[\"3\"]}"
    + val input_str: String = "{\"in\":[\"0\",\"0\",\"1\",\"0\",\"1\",\"1\",\"1\",\"0\",\"1\",\"0\",\"1\",\"0\",\"0\",\"1\",\"1\",\"0\",\"1\",\"1\",\"0\",\"0\",\"1\",\"1\",\"1\",\"0\",\"0\",\"0\",\"1\",\"0\",\"1\",\"1\",\"1\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\",\"0\"]}"
  1. Then Run the app again like in step 5.

7. Update Rust exported functions​

Currently, only generateCircomProof and verifyCircomProof are available with the bindings, but the bindings can be extended to support nearly all Rust functions.

Here is an example demonstrating how to use the Semaphore crate.

  1. Update Cargo.toml

    Import semaphore crate from: https://github.com/worldcoin/semaphore-rs

    info

    We are using this specific commit 340d4ad for semaphore-rs.

    Cargo.toml
    semaphore-rs = { git = "https://github.com/worldcoin/semaphore-rs", features = ["depth_16"], rev = "340d4ad"}

  2. Define a function to generate semaphore proof

    Here is an example to define semaphore prove and verify in src/lib.rs

    Alternatively, we can create a demo function called semaphore() to run the code from the README.

    src/lib.rs
    use semaphore_rs::{get_supported_depths, hash_to_field, Field, identity::Identity,
                poseidon_tree::LazyPoseidonTree, protocol::*};

    pub fn semaphore() {
        // generate identity
        let mut secret = *b"secret";
        let id = Identity::from_secret(&mut secret, None);

        // Get the first available tree depth. This is controlled by the crate features.
        let depth = get_supported_depths()[0];

        // generate merkle tree
        let leaf = Field::from(0);
        let mut tree = LazyPoseidonTree::new(depth, leaf).derived();
        tree = tree.update(0, &id.commitment());

        let merkle_proof = tree.proof(0);
        let root = tree.root();

        // change signal and external_nullifier here
        let signal_hash = hash_to_field(b"xxx");
        let external_nullifier_hash = hash_to_field(b"appId");

        let nullifier_hash = generate_nullifier_hash(&id, external_nullifier_hash);

        let proof = generate_proof(&id, &merkle_proof, external_nullifier_hash, signal_hash).unwrap();
        let success = verify_proof(root, nullifier_hash, signal_hash, external_nullifier_hash, &proof, depth).unwrap();

        assert!(success);
    }
    warning

    You can also try returning a value; otherwise, nothing will happen after execution. e.g.

    pub fn semaphore() -> bool {
        // ...
        return success;
    }

  3. Export the function through UniFFI procedural macros

    You can simply use the UniFFI proc-macros (e.g. #[uniffi::export]) to define the function interfaces.

    info

    For more details, refer to the UniFFI documentation.

    + #[uniffi::export]
    pub fn semaphore() {
        // generate identity
        let mut secret = *b"secret";
        ...

  4. Run mopro build again and manually update the bindings for iOS and Android as explained in Step 6.

  5. You can now call the semaphore() function you just defined on both iOS and Android. 🎉

8. Conclusion​