AirCipher 🌐

⚡ Secure. Offline. Peer-to-Peer.

AirCipher is a next-generation privacy-focused communication app built for environments without internet connectivity. It enables real-time voice calling and secure messaging directly over local networks using WebRTC and cryptographic protocols. By eliminating the need for central servers, AirCipher offers a truly offline-first experience while maintaining strong security and low-latency performance.

The core innovation lies in combining peer discovery, identity authentication, and encryption into a seamless local-first stack—ideal for educational campuses, secure internal networks, or remote areas.

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✨ Features

• 🔗 Offline peer discovery via UDP broadcast
• 📞 Real-time voice calling & messaging over local Wi-Fi (no internet required)
• 🔐 End-to-end encryption (X25519 + Ed25519 + AES-256-GCM)
• ❄️ Pure ICE negotiation (no STUN/TURN servers)
• ❌ Zero reliance on external servers or cloud infrastructure
• 📡 Lightweight, low-latency local communication

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🛠 Tech Stack

Category	Tools / Protocols
Language	Dart (Flutter)
Networking	WebRTC, UDP (RawDatagramSocket), ICE
Encryption	X25519 (Key Exchange), Ed25519 (Auth), AES-GCM
Serialization	JSON
Platforms	Android

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🔐 Security Architecture

AirCipher implements a custom end-to-end encryption protocol:

• ↻ X25519 for Elliptic Curve Diffie-Hellman (ECDH) key exchange
• ✅ Ed25519 for peer identity verification via digital signatures
• 🛡 AES-256-GCM for authenticated encryption of all media and messages

Each session is uniquely encrypted and authenticated. No data is stored or transmitted outside the device or network.

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🧹 How It Works

🔍 1. Peer Discovery

Peers broadcast availability and identity over local Wi-Fi using UDP broadcast.

🔑 2. Key Exchange & Authentication

Peers exchange X25519 public keys, signed with Ed25519 identities for authenticity.

❄️ 3. Connection Establishment

A direct WebRTC peer-to-peer connection is negotiated using ICE without external signaling (STUN/TURN).

💬 4. Messaging and Calls

All communication—both text and media—is securely encrypted and transmitted over the direct channel using data channels and SDP audio tracks.

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🧭 Workflow Diagram

graph TD;
    A[Device A] -- UDP Broadcast --> B[Device B]
    B -- Discovery Response --> A
    A --> C[X25519 + Ed25519 Key Bundle Signed]
    B --> D[Verify Signature & Compute Shared Secret]
    A --> E[WebRTC ICE Negotiation]
    B --> F[Establish Peer Connection]
    E --> G[Encrypted DataChannel / VoiceStream]
    F --> G
    G --> H[Encrypted Communication]

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🚀 Getting Started

Prerequisites

• Flutter SDK (v3.10 or later)
• Android Studio or VS Code
• Devices on the same local network

Run the App

flutter pub get
flutter run

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📂 Project Structure

lib/
├── core/              # Core models, enums, utils
├── network/           # Discovery, signaling, and WebRTC logic
├── features/          # App screens and widgets
└── main.dart          # Entry point

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