OpenAC Taiwan Citizen Digital Certificate iOS Example

An iOS example app that integrates Taiwan's Citizen Digital Certificate (TW FidO) with openac-rsa-x509-swift to generate a zero-knowledge proof from the certificate signature and send it to a server for verification.

Demo

Download Circuits	Sign with MOICA	Generate Proof
~10 seconds	~11 seconds	prove ~5 s | verify ~13 s

Setup Card

Always visible. Shows download progress for the files below (shown only when not yet present); the MOICA and ZK Pipeline sections are hidden until all three are ready.

• Download Circuit — fetches and decompresses cert_chain_rs4096_proving.key, user_sig_rs2048_proving.key (zkID releases), and g3-tree-snapshot.json.gz (moica-revocation-smt releases)

TW FidO / MOICA Card (visible after circuit + keys are ready)

Enter your ID Number (身分證字號), then follow the steps:

• TBS — to-be-signed challenge bytes; tap the refresh button to call POST /challenge on the server and receive a challenge_bytes
• Get SP Ticket — calls POST /fido/sp-ticket with the ID number and TBS; returns a signed sp_ticket
• Verify with MOICA — deep-links to mobilemoica://moica.moi.gov.tw/a2a/verifySign so the MOICA app performs the signature; returns to openac://callback
• Auth Result — calls POST /fido/ath-result, polling until the signed response and signer certificate are available
• Generate Input — calls generateCertChainRs4096Input from openac-rsa-x509-swift to build the circuit input JSON from the MOICA response, issuer certificate, TBS, and SMT snapshot

ZK Pipeline Card (visible after circuit + keys are ready)

• Generate Proof — runs proveCertChainRs4096 and proveUserSigRs2048 (Groth16 provers); reports time in ms
• Verify — submits proofs to POST /link-verify with the challenge ID and cert chain type (rs4096)
• Run All Steps — convenience button in the toolbar that runs prove + verify in sequence

Link-verify request format

{
    "cert_chain_type": "rs4096",
    "cert_chain_proof": "<base64-encoded bytes>",
    "user_sig_proof": "<base64-encoded bytes>"
}

Getting Started

Clone the repo and open it in Xcode.

git clone https://github.com/privacy-ethereum/openac-taiwan-citizen-digital-certificate-ios-example

1. Start the verifier server

Clone and run go-zkid-verifier, then expose it via ngrok:

# In the go-zkid-verifier directory
make download-keys
make build
make serve

# In a separate terminal
ngrok http 8080

ngrok will print a public URL like https://b33f-54-237-15-198.ngrok-free.app. Copy it.

2. Update the server URLs in the app

Open OpenACExampleApp/ProofViewModel.swift and replace the two URL constants near the top of the file with your ngrok URL:

private let serverURL = URL(string: "https://<your-subdomain>.ngrok-free.app/challenge")!
private let linkVerifyURL = URL(string: "https://<your-subdomain>.ngrok-free.app/link-verify")!

3. Configuration — Secrets.swift

The app requires TW FidO SP service credentials. Apply for these as an SP (Service Provider) at https://fido.moi.gov.tw/pt/, then create or update the file below before building (it is git-ignored):

OpenACExampleApp/Secrets.swift

enum Secrets {
    static let fidoSpServiceID = "your-sp-service-id"
    static let fidoAESKey      = "your-32-byte-aes-key-base64"
}

Constant	Description
fidoSpServiceID	SP service ID issued by MOICA for TW FidO
fidoAESKey	32-byte AES-256 key (base64-encoded) used to compute sp_checksum via AES-256-GCM

Credentials can also be supplied at test time via environment variables FIDO_SP_SERVICE_ID and FIDO_AES_KEY; the app falls back to Secrets.swift if those are absent.

4. Build and run

1. Open OpenACExampleApp.xcodeproj in Xcode (open . -a Xcode).
2. Select a physical iPhone and ensure the TW FidO app (行動自然人憑證) is installed.
3. Build and run.
4. On first launch, tap Download Circuit in the Setup section and wait for all three files to download.
5. Tap the refresh button next to TBS to fetch a challenge from the server.
6. Enter your ID number (身分證字號), then follow the TW FidO / MOICA steps in order.
7. Tap Run All Steps (or individual play buttons) to generate and verify the ZK proofs.

Requirements

• iOS 16+
• Xcode 15+
• MOICA app installed on device for the authentication flow
• A running server exposing /challenge and /link-verify endpoints

Dependencies

• openac-rsa-x509-swift — Swift bindings for proveCertChainRs4096, proveUserSigRs2048, verifyCertChainRs4096, verifyUserSigRs2048, generateCertChainRs4096Input
• CryptoKit (system) — AES-256-GCM for the sp_checksum required by the TW FidO API
• zlib (system) — decompresses .gz key files on-device

See also

• openac-rsa-x509-swift — API, installation, and prebuilt binaries
• zkID releases — circuit and key files
• moica-revocation-smt — SMT snapshot releases

Community

• X account:
• Telegram group:

Acknowledgements

It is currently incubated by PSE.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.