zkTLS Integration using Opacity in a Xion Mobile App

The ability to verify real-world facts without compromising user privacy is critical. Traditional methods of user verification can introduce trust assumptions, privacy tradeoffs, and central points of failure.

zkTLS (Zero-Knowledge Transport Layer Security) bridges this gap by allowing clients to generate verifiable proofs of HTTPS interactions, without revealing the full response or needing to trust the server. This has massive implications for Apps:

• Trustless verification of real-world data from web2 sources (e.g., social platforms, email providers, SaaS tools)

• Privacy-preserving: users reveal only what's necessary, not the full data

• On-chain utility: proofs can be verified by smart contracts for gating access or triggering functionality

Prerequisites

Before you begin, ensure you have the following installed and configured:

• Node.js (LTS version recommended) and npm

• An Android Emulator via Android Studio, iOS Simulator via Xcode, or a physical mobile device for testing

The following guide will help you set up your local development environment for Expo. We also have a guide to help Set up your XION Mobile Development Environment, which shows how to get your Android emulator and iOS simulator set up.

Create an Opacity Account

Opacity is a decentralized identity protocol that allows users to prove facts about themselves, such as social media stats, financial data, or platform activity, using zero-knowledge proofs (ZKPs). Rather than sharing raw data, Opacity enables users to generate cryptographic proofs that can be verified on-chain without revealing the underlying information.

In this guide, we’ll use Opacity to let users prove their Github follower count without exposing their full profile or login credentials. This is done through Opacity’s integration with trusted data providers like Github, wrapped in a ZK-proof that can be verified by your frontend or smart contract.

To get started, you’ll need to:

1. Visit Opacity and sign up for a developer account.

2. Navigate to the "Billing" menu to purchase credits.

3. Select "API Keys" from the menu.

4. Click "New key" add a label, and select "Create secret key"

5. Copy and store the generated key as you'll need it for the demo app.

Opacity's Verification Contract

Opacity provides a verifier contract deployed on XION testnet that validates zkTLS proof signatures on-chain. This ensures the GitHub data hasn't been tampered with.

Contract Address (Testnet):

xion1n5hj97fw96ef40t6h7e46lqhxsyr6fml02sjfrhk382cdl2z736qnq0yd0

Query Message Format:

{
  "verify": {
    "signature": "0x...",
    "message": "<data_string_from_opacity>"
  }
}

The contract returns true if the signature is valid, confirming the data came from Opacity and wasn't modified.

Deploy Required Contracts

Go to https://quickstart.dev.testnet.burnt.com, log in with your wallet, and select the User Map contract type. Then click Launch User Map & Fund Treasury to deploy both contracts.

1. For the automated installer, click the "One-liner (Recommended)" tab under "Step 4" and copy the bash command and execute it in your terminal.

1. Follow the prompts in the terminal:

1. We only need the User Map (EXPO_PUBLIC_USER_MAP_CONTRACT_ADDRESS) and Treasury (EXPO_PUBLIC_TREASURY_CONTRACT_ADDRESS) contract addresses generated for the demo app. Go into the xion-mobile-quickstart directory and copy these values from the .env.local file.

User Map Contract

The User Map contract stores arbitrary JSON data per user address. We use it to persist GitHub verification results on-chain.

Execute Message (Store Data):

{
  "update": {
    "value": "{\"github\":{\"followers\":7,\"isFamous\":true,...}}"
  }
}

Query Message (Read Data):

{
  "get_value_by_user": {
    "address": "xion1..."
  }
}

Data Schema:

interface VerificationData {
  followers: number;        // GitHub follower count
  isFamous: boolean;        // true if followers > following
  verifiedAt: string;       // ISO timestamp of verification
  verificationValid: boolean; // On-chain signature verification result
}

Set up Mobile App

We've built a demo app to showcase how everything works together. In this example, we retrieve a user's followers count from github.com and store that value in the User Map contract datastore.

1. In your terminal clone the repository and change into the newly created project directory:

git clone https://github.com/emperorjm/opacity-expo-demo
cd opacity-expo-demo

1. Install dependencies:

npm install

1. Copy the .env.example and rename it .env.local and add the User Map address value generated above to EXPO_PUBLIC_USER_MAP_CONTRACT_ADDRESS and add the generated Treasury contract address to EXPO_PUBLIC_TREASURY_CONTRACT_ADDRESS.

EXPO_PUBLIC_RPC_ENDPOINT="https://rpc.xion-testnet-2.burnt.com:443"
EXPO_PUBLIC_REST_ENDPOINT="https://api.xion-testnet-2.burnt.com"

EXPO_PUBLIC_TREASURY_CONTRACT_ADDRESS="treasury-contract-address"

EXPO_PUBLIC_USER_MAP_CONTRACT_ADDRESS="your-user-map-contract-address"

EXPO_PUBLIC_OPACITY_API_KEY="your-opacity-app-key"
EXPO_PUBLIC_OPACITY_VERIFIER_CONTRACT="opacity-verifier-contract"

Variable	Description
EXPO_PUBLIC_TREASURY_CONTRACT_ADDRESS	Treasury contract instance used for gasless transactions and grants authorization to execute transactions via the User Map smart contract instance on behalf of users. You will also need to add your RUM contract address to the treasury contract permission to allow for executing transactions on the user's behalf.
EXPO_PUBLIC_RPC_ENDPOINT	RPC endpoint for Xion (default: https://rpc.xion-testnet-2.burnt.com:443)
EXPO_PUBLIC_REST_ENDPOINT	REST endpoint for Xion (default: https://api.xion-testnet-2.burnt.com)
EXPO_PUBLIC_USER_MAP_CONTRACT_ADDRESS	Your User Map contract instance where the user's follower count will be added to their user map record with their logged in wallet address being the key
EXPO_PUBLIC_OPACITY_API_KEY	API key for interacting with the Opacity platform.
EXPO_PUBLIC_OPACITY_VERIFIER_CONTRACT	Validates that the zkTLS proofs were legitimately signed by authorized notary nodes and haven't been tampered with.

1. Build and launch the application:

To build and run the app, ensure your emulator, simulator, or physical device is running. Then, use one of the following commands based on your target platform to launch the App:

For Android

npx expo run:android

For iOS