Private Contact Discovery (Arcium)

Overview

This project allows users to find friends on a platform without exposing their contact list.

Instead of uploading raw contacts, the system uses privacy-preserving matching so that:

• Only matches are revealed
• Non-matching contacts remain completely private

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Problem

Most apps like WhatsApp, Telegram, etc. require users to upload their entire contact list on their platform.

This leads to:

• Privacy leaks
• Centralized data collection
• Risk of misuse

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Solution

This project implements Private Set Intersection (PSI) logic:

• Contacts are hashed and encoded
• Matching is done on encrypted values
• Only common contacts are returned

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Arcium Integration

In a production setup:

• Contacts are encrypted client-side
• Arcium performs computation using MPC (Multi-Party Computation)
• No party (server or nodes) can see raw data
• Only matches are revealed

Current implementation simulates PSI logic, but backend is designed to integrate Arcium directly.

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Tech Stack

• Node.js
• Express
• JWT Authentication
• Crypto (SHA256 hashing)
• Solana (devnet ready)
• Arcium (conceptual integration)

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Project Structure

arcium_private_contact/ │ ├── src/

│ ├── routes/

│ │ └── contacts.js

│ ├── services/

│ │ ├── hashService.js

│ │ ├── authService.js

│ │ └── arciumClient.js

│ ├── data/

│ │ └── users.js

│ └── index.js │ ├── .env

├── package.json

└── README.md

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Installation & Setup

Getting Started

Follow these steps to run the backend locally.

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Update System (Optional)
sudo apt update && sudo apt upgrade -y


1. Install Node.js (if not installed)

Check if Node.js exists:
 node -v

If not installed:
 sudo apt install nodejs npm -y


2. Clone the Repository:
git clone https://github.com/salauayo/arcium_private_contact.git
cd arcium_private_contact


3. Install Dependencies
npm install


4. Create Environment Variables:

Create a .env file:
nano .env

Paste:

RPC_URL=https://api.devnet.solana.com
ARCIUM_CLUSTER_OFFSET=1
KEYPAIR_PATH=/home/salauayo/.config/solana/id.json
MXE_PROGRAM_ID=placeholder

⚠️(Replace SALAUAYO with your system username)


5. (Optional) Install Solana CLI;
Only needed if you want blockchain interaction:

sh -c "$(curl -sSfL https://release.solana.com/stable/install)"
export PATH="$HOME/.local/share/solana/install/active_release/bin:$PATH"
solana --version


6. Start the Backend Server
npm start

You should see:
Server running on port 3000
 Testing the API

1. Login:
curl -X POST http://localhost:3000/api/login \
-H "Content-Type: application/json" \
-d '{"username":"alice","password":"password123"}'

2. Find Friends (Private Matching)
curl -X POST http://localhost:3000/api/find-friends \
-H "Authorization: Bearer YOUR_TOKEN" \
-H "Content-Type: application/json" \
-d '{"contacts":["elon@yahoo.com","friend@gmail.com"]}'

How It Works

• User logs in
• Sends contact list
• Contacts are hashed + encoded
• System compares encrypted values
• Only matches are returned

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Impact

• Prevents contact data leaks
• Enables privacy-first onboarding

_ Can be used in:

• Messaging apps
• Social networks
• Fintech platforms

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Future Improvements

• Full Arcium MPC integration
• Frontend UI
• Wallet-based authentication
• Real encrypted computation

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Advanced Setup (Arcium + Solana)

1. Install solana CLI

sh -c "$(curl -sSfL https://release.solana.com/stable/install)"

Reload Terminal

export PATH="$HOME/.local/share/solana/install/active_release/bin:$PATH"

check installation

solana --version

2. Generate a wallet

solana-keygen new

this create a keypair at:

~/.config/solana/id.json

3. Airdrop Solana Devnet

solana config set --url devnet solana airdrop 2

Check Balance

solana balance

4. Make sure your .env contains

RPC_URL=https://api.devnet.solana.com ARCIUM_CLUSTER_OFFSET=1 KEYPAIR_PATH=/home/salauayo/.config/solana/id.json MXE_PROGRAM_ID=placeholder

5. Test Solana Connection

node testSolana.js

Expected output

Connected to Solana! Current slot: XXXXX

Arcium Integration Note;

• Current implementation uses simulated Private Set Intersection (PSI)

• Backend structure supports encrypted computation flow

• In full Arcium setup: contacts are encrypted before submission, MPC nodes compute matches, only matches are revealed

• Full Arcium MPC integration

• Frontend UI

• Wallet-based authentication

• Real encrypted computation