SCN - Secure Connection Network

Secure file and message sharing over local network

Cross-platform application for transferring files and chatting between devices without internet

About

SCN (Secure Connection Network) is a simplified version of an application for secure file and message sharing between devices over a local network. Unlike other solutions, SCN does not require an internet connection or external servers - all data is transmitted directly between devices.

Features

• ✅ Secure file sharing - Transfer files between devices on local network
• ✅ Real-time chat - Exchange text messages between devices
• ✅ Automatic device discovery - UDP multicast for finding devices on network
• ✅ Secure mesh network - Connect remote peers over the internet via signaling + WebRTC foundation
• ✅ TURN-ready fallback - Relay path for symmetric NAT, CGNAT and mobile networks
• ✅ Simple architecture - Flutter/Dart only, no complex dependencies
• ✅ Cross-platform - Windows, Linux, macOS (in development)
• ✅ Privacy - Works without external servers, all data transmitted directly

Technologies

• Flutter - UI and cross-platform development
• Dart - All application logic
• shelf - HTTP server for receiving files
• multicast_dns - Device discovery on network
• Provider - State management
• WSL - Windows Subsystem for Linux (for building Linux on Windows)

Installation and Setup

Requirements

• Flutter SDK 3.25.0 or higher
• Windows 10+ (for Windows builds)
• Linux (Ubuntu 20.04+, Debian 11+, or similar) - for Linux builds
• WSL (Windows Subsystem for Linux) - for building Linux on Windows

Building from Source

1. Clone the repository:

git clone https://github.com/hvkeyn/scn.git
cd scn

2. Navigate to project directory:

cd scn

3. Install dependencies:

flutter pub get

4. Build the project:

# Windows
flutter build windows

# Or use build script (from project root)
cd ..
.\build.ps1 -Platform windows

# Linux (native or WSL)
chmod +x build.sh
./build.sh

# Note: For Windows, you need Ubuntu WSL. See LINUX_BUILD.md for details.

# Or from scn directory
cd scn
flutter build linux --release

Pre-built Releases

Windows release is located in scn-release/ folder:

scn-release/
├── scn.exe                 - Main executable
├── flutter_windows.dll     - Flutter engine
├── data/                   - Application data
│   ├── app.so             - Compiled code
│   ├── icudtl.dat         - ICU data
│   └── flutter_assets/    - Resources
└── README.txt             - Instructions

Linux release is located in scn-release-linux/ folder:

scn-release-linux/
├── scn                     - Main executable
├── lib/                    - Application libraries
├── data/                   - Application data
│   └── flutter_assets/   - Resources
└── README.txt             - Instructions

Run:

• Windows: Double-click scn.exe or run: .\scn.exe
• Linux: Make executable: chmod +x scn, then run: ./scn

Usage

Network Setup

For the application to work, you need to:

1. Configure firewall:

   • Allow incoming TCP/UDP connections on port 53317 (HTTP/Discovery)
   • Allow outgoing connectivity to signaling and TURN services
   • Allow outgoing TCP/UDP connections

2. Disable AP Isolation:

   • Make sure AP Isolation is disabled on your router
   • This is necessary for device discovery on network

3. Set network as "Private":

   • On Windows: configure network as "Private" (not "Public")

4. For remote connections:

   • Prefer invite tokens through signaling backend
   • Keep TURN available as standard fallback
   • Router port forwarding is optional and mainly helps legacy direct mode

Main Features

• Send files: Select files and send them to another device
• Receive files: Receive files from other devices on network
• Chat: Exchange messages with devices on network
• Settings: Change device name, port and other parameters

Project Structure

scn/
├── lib/
│   ├── main.dart              - Entry point
│   ├── services/              - Application services
│   │   ├── app_service.dart           - Main service
│   │   ├── http_server_service.dart   - HTTP server
│   │   ├── http_client_service.dart   - HTTP client
│   │   ├── discovery_service.dart     - Device discovery
│   │   ├── secure_channel_service.dart - WebSocket/TLS channel
│   │   ├── mesh_network_service.dart  - Mesh network
│   │   └── file_service.dart          - File operations
│   ├── pages/                 - Application pages
│   │   ├── home_page.dart            - Main page
│   │   └── tabs/                     - Tabs
│   │       ├── receive_tab.dart      - Receive files
│   │       ├── send_tab.dart         - Send files
│   │       ├── chat_tab.dart         - Chat
│   │       └── settings_tab.dart     - Settings
│   ├── providers/             - State management
│   │   ├── device_provider.dart      - Devices
│   │   ├── receive_provider.dart     - Receive state
│   │   ├── send_provider.dart        - Send state
│   │   ├── chat_provider.dart        - Chat state
│   │   └── remote_peer_provider.dart - Remote peers
│   ├── models/                - Data models
│   │   ├── device.dart              - Device model
│   │   ├── file_info.dart           - File information
│   │   ├── session.dart             - Transfer session
│   │   ├── chat_message.dart        - Chat message
│   │   ├── multicast_dto.dart       - Multicast data
│   │   └── remote_peer.dart         - Remote peer model
│   └── widgets/               - Widgets
│       ├── scn_logo.dart            - SCN logo
│       ├── add_peer_dialog.dart     - Add peer dialog
│       ├── invitation_card.dart     - Invitation card
│       └── peer_tile.dart           - Peer list tile
├── windows/                   - Windows configuration
├── linux/                     - Linux configuration
├── pubspec.yaml              - Dependencies
└── README.md                 - This file

Protocol

SCN uses a simple HTTP-based protocol for data exchange:

Local Network

• Device discovery: UDP multicast on port 53317
• HTTP server: TCP on port 53317 (default)
• API endpoints:
  • GET /api/info - Device information
  • POST /api/register - Device registration
  • POST /api/session - Create transfer session
  • POST /api/accept - Accept files
  • POST /api/upload - Upload file
  • POST /api/chat - Send message

Secure Mesh Network

• Secure channel: WebSocket over TLS on port 53318 (default)
• Mesh sync: Automatic peer list propagation
• Authentication: Optional password protection
• Message types: handshake, peerList, invitation, data, ping/pong

Development

Running in Development Mode

Windows:

cd scn
flutter run -d windows

Linux:

cd scn
flutter run -d linux

Testing

cd scn
flutter test

Building Release

Windows:

.\build.ps1 -Platform windows

Result will be in scn-release/ folder.

Linux (native or WSL):

chmod +x build.sh
./build.sh

Result will be in scn-release-linux/ folder.

Linux on Windows (via WSL):

.\build.ps1 -Platform linux

The script will automatically detect and use Ubuntu WSL if available.

Note: For building Linux on Windows, you need Ubuntu WSL installed (not just docker-desktop). See LINUX_BUILD.md for detailed setup instructions.

Compatibility

Platform	Minimum Version	Status
Windows	10	✅ Supported
Linux	Ubuntu 20.04+	✅ Supported
macOS	-	🚧 In development
Android	-	📋 Planned
iOS	-	📋 Planned

Troubleshooting

Devices can't see each other

1. Check that both devices are on the same network
2. Make sure AP Isolation is disabled on router
3. Check firewall settings
4. On Windows: set network as "Private"

Files not transferring

1. Check that server is running (in settings)
2. Make sure port 53317 is not occupied by another application
3. Check application logs

Slow transfer speed

1. Use 5 GHz Wi-Fi instead of 2.4 GHz
2. Make sure devices are on the same subnet
3. Check network load

License

This project is based on LocalSend and uses a simplified architecture.

Contributing

We welcome contributions to the project! If you want to help:

1. Create an issue to discuss changes
2. Fork the repository
3. Create a pull request with description of changes

Version

Current version: 1.0.0+16

Contacts

• GitHub: https://github.com/hvkeyn/scn
• Issues: https://github.com/hvkeyn/scn/issues

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Made with ❤️ for secure file sharing