Secure Messaging System - Installation & Setup

Requirements

Before running the secure messaging system, you need to install the required dependencies:

pip install cryptography

Project Structure

The secure messaging system consists of two main components:

1. Server (server.py) - Handles client connections, key exchange, and message routing
2. Client (client.py) - GUI application for users to send and receive encrypted messages

Features Implemented

🔐 End-to-End Encryption

• RSA Encryption: Used for secure asymmetric key exchange (2048-bit keys)
• AES Encryption: Used for fast symmetric encryption of message content (256-bit keys)
• Caesar Cipher: Additional layer of encryption as specified in requirements

🏗️ Architecture

• Client-Server Model: Python socket-based real-time communication
• Multi-threaded Server: Handles multiple clients simultaneously
• Modern GUI: Built with tkinter for user-friendly interface

🛡️ Security Features

• Public key infrastructure for secure key exchange
• Unique AES key for each message
• Caesar cipher preprocessing
• Message integrity and privacy protection

How to Run

1. Start the Server

First, run the server in one terminal:

python3 server.py

The server will start listening on localhost:12345 by default.

2. Start Client(s)

In separate terminals, run the client application:

python3 client.py

You can run multiple clients to test the messaging between different users.

Usage Instructions

Connecting to Server

1. Enter a unique username
2. Specify server address (default: localhost:12345)
3. Click "Connect"

Sending Messages

1. Select a recipient from the dropdown
2. Set Caesar cipher shift value (0-25)
3. Type your message
4. Click "Send Encrypted Message" or press Enter

Security Process

1. Message Input: User types plaintext message
2. Caesar Encryption: Message encrypted with specified shift
3. AES Encryption: Caesar-encrypted message encrypted with unique AES key
4. RSA Encryption: AES key encrypted with recipient's public key
5. Transmission: Encrypted key and message sent to server
6. Decryption: Recipient reverses the process to read the message

Technical Details

Encryption Flow

Original Message → Caesar Cipher → AES Encryption → RSA Key Exchange → Secure Transmission

Key Management

• Each client generates a 2048-bit RSA key pair
• Public keys are exchanged through the server
• AES keys are generated per message for perfect forward secrecy
• Caesar shift can be adjusted per message

Network Protocol

• JSON-based message protocol
• Base64 encoding for binary data
• Real-time socket communication
• Automatic user list updates

Customization

Server Configuration

You can modify the server host and port in server.py:

server = SecureMessagingServer(host='0.0.0.0', port=8080)

Client Configuration

Default server address can be changed in the client GUI or modify the default in client.py.

Encryption Parameters

• RSA key size: Currently 2048 bits (can be increased for more security)
• AES key size: 256 bits
• Caesar shift: Configurable 0-25

Security Notes

⚠️ Important: This is a demonstration/educational implementation. For production use, consider:

• Certificate-based authentication
• Perfect forward secrecy improvements
• Message authentication codes (MAC)
• Protection against timing attacks
• Secure key storage
• User authentication beyond usernames

Troubleshooting

Common Issues

1. Connection Refused: Make sure server is running first
2. Username Taken: Choose a different username
3. Encryption Errors: Ensure recipient is online and keys are exchanged
4. Module Not Found: Install cryptography package with pip

Debug Tips

• Check server terminal for connection logs
• Verify firewall settings if connecting remotely
• Ensure Python version compatibility (3.6+)