# SCAR Chat Application

A cross-platform GUI chat client and server with SSL/TLS encryption, built in C++.

## Features

### Server (`chat_server`)
- Listens on TCP port **42317** with TLS/SSL encryption
- Multi-client support with broadcast messaging
- Uses OpenSSL for secure communication
- Linux/cross-platform compatible

### Qt Client (`chat_client_qt`)
- Cross-platform GUI using Qt5/6 Widgets
- TLS/SSL encrypted connection to server
- **Customizable UI:**
  - Background color selector for all windows
  - Chat text color customization
  - Transparency/opacity slider (0-100%)
- Message history display
- Real-time message sending and receiving
- Linux/cross-platform compatible

### Windows Client (`chat_client_win`)
- Native Win32 GUI client
- Same UI features as Qt client
- Windows-only build

## Prerequisites

### Linux / macOS
```bash
# Ubuntu/Debian
sudo apt-get install cmake qtbase5-dev libssl-dev build-essential

# macOS (Homebrew)
brew install cmake qt5 openssl
```

### Windows
- Visual Studio 2019+ or MinGW
- CMake 3.16+
- Qt5/6 SDK
- OpenSSL for Windows (vcpkg or prebuilt binaries)

## Building

### Linux / macOS

1. **Create and generate certificates:**
   ```bash
   cd certs
   ./generate_certs.sh
   cd ..
   ```

2. **Build the project:**
   ```bash
   mkdir build
   cd build
   cmake ..
   make
   ```

3. **Install (optional):**
   ```bash
   make install
   ```

### Windows

1. **Generate certificates** (use OpenSSL for Windows or WSL):
   ```bash
   cd certs
   # On Windows, use Git Bash or WSL to run generate_certs.sh
   # Or generate manually using OpenSSL
   cd ..
   ```

2. **Build:**
   ```bash
   mkdir build
   cd build
   cmake -G "Visual Studio 16 2019" ..
   cmake --build . --config Release
   ```

## Running

### Server

```bash
# Linux / macOS
./build/chat_server certs/server.crt certs/server.key

# Windows
.\build\Release\chat_server.exe certs\server.crt certs\server.key
```

The server will listen on `localhost:42317`.

### Qt Client

```bash
# Linux / macOS
./build/chat_client_qt

# Windows (if built on Windows)
.\build\Release\chat_client_qt.exe
```

Connect to server by entering host/port and clicking "Connect".

### Windows Client

```bash
# Windows only
.\build\Release\chat_client_win.exe
```

## Customization Features

### Background Color
- Click "BG Color" button to select background color for all windows
- Color choice is applied immediately

### Text Color
- Click "Text Color" button to select chat text color
- Updates chat display in real-time

### Transparency
- Use the transparency slider (0-100%) to adjust window opacity
- 0% = fully transparent, 100% = fully opaque

## SSL/TLS Certificates

### Generate Self-Signed Certificates

For development and testing:

```bash
cd certs

# Generate private key
openssl genrsa -out server.key 2048

# Generate certificate (valid for 365 days)
openssl req -new -x509 -key server.key -out server.crt -days 365 \
  -subj "/C=US/ST=State/L=City/O=SCAR/CN=localhost"

cd ..
```

**Note:** For production, use certificates signed by a trusted Certificate Authority (CA).

### Ignoring Self-Signed Certificates

The Qt client is configured to ignore self-signed certificate errors during development:
```cpp
socket->ignoreSslErrors();
```

For production, implement proper certificate validation.

## Project Structure

```
scar-chat/
├── CMakeLists.txt          # Top-level CMake configuration
├── README.md               # This file
├── certs/                  # SSL certificates directory
│   └── generate_certs.sh   # Certificate generation script
├── src/
│   ├── server/
│   │   └── server.cpp      # TLS server (OpenSSL)
│   ├── qt_client/
│   │   └── main.cpp        # Qt GUI client
│   └── windows_client/
│       └── main_win.cpp    # Win32 GUI client
└── build/                  # Build output directory (created after cmake)
```

## Troubleshooting

### "Connection refused" error
- Ensure server is running on the same host/port
- Check firewall settings on port 42317

### SSL/TLS errors
- Verify certificates exist in `certs/` directory
- Regenerate certificates if expired or corrupted
- Ensure certificate and key files are readable

### Qt not found during CMake
```bash
# Set Qt path explicitly
cmake -DQt5_DIR=/path/to/Qt5/lib/cmake/Qt5 ..
```

### OpenSSL not found during CMake
```bash
# Set OpenSSL path explicitly (macOS example)
cmake -DOPENSSL_DIR=/usr/local/opt/openssl ..
```

## Development Notes

- **C++17** standard is required
- **Qt5/6** for cross-platform GUI
- **OpenSSL 1.1+** for TLS/SSL
- Threading used for non-blocking socket operations
- Message protocol: simple newline-delimited UTF-8 text

## Security Considerations

- ✅ Uses TLS 1.2+ for encrypted communication
- ⚠️ Development mode: ignores self-signed certificate errors
- ⚠️ No user authentication implemented
- ⚠️ No message encryption at application level (relies on TLS)

For production use, implement:
- Proper certificate validation
- User authentication and authorization
- Message signing/verification
- Rate limiting and DoS protection

## License

This project is provided as-is for educational and development purposes.