MessageU - End-to-End Encrypted Messaging System

A secure client-server messaging application implementing end-to-end encryption, similar to WhatsApp or Facebook Messenger, developed as part of the Defensive Systems Programming course (20937).

📋 Overview

This project implements a pull-based messaging system where clients send messages to a server, which then distributes them to target recipients. The system supports end-to-end encryption, ensuring that only the intended recipients can read the messages.

Key Features

• End-to-End Encryption: Messages are encrypted on the client side and can only be decrypted by the intended recipient
• Pull-based Architecture: Clients periodically request messages from the server
• Multi-user Support: Server handles multiple concurrent clients using threads or selectors
• Offline Message Support: Messages are stored for offline users and delivered when they come online
• File Transfer: Support for sending encrypted files between users (bonus feature)

🏗️ Architecture

Server (Python)

• Language: Python 3
• Protocol: Stateless over TCP
• Database: SQLite (defensive.db) for persistent storage
• Port Configuration: Reads from myport.info file
• Version: 2.0 (for bonus features)

Client (C++)

• Language: C++
• Interface: Console-based application
• Encryption: RSA + AES hybrid encryption
• Configuration: Reads server info from server.info and user info from my.info
• Version: 2.0 (for bonus features)

📁 Project Structure

src/
├── client/          # C++ client implementation
│   ├── *.cpp        # Source files
│   └── *.h          # Header files
└── server/          # Python server implementation
    └── *.py         # Python source files

🔧 Setup and Installation

Prerequisites

Server Requirements:

• Python 3.x
• SQLite3 (included with Python)

Client Requirements:

• C++ compiler (Visual Studio Community 2019 recommended)
• Crypto++ library (version 8.8.0+)
• Winsock or Boost libraries for networking

Configuration Files

1. Server Port Configuration (myport.info):

   1234
   

2. Client Server Configuration (server.info):

   127.0.0.1:1234
   

3. Client User Configuration (my.info):

   Michael Jackson
   64f3f63985f04beb81a0e43321880182
   MIGdMA0GCSqGSIb3DQEBA...
   

🚀 Usage

Server

cd src/server
python server.py

Client

cd src/client
./client.exe

Client Menu Options

MessageU client at your service.
110) Register
120) Request for client list
130) Request for public key
140) Request for waiting messages
150) Send a text message
151) Send a request for a symmetric key
152) Send your symmetric key
153) Send a file (bonus)
0) Exit client

🔐 Security Features

Encryption Implementation

• Asymmetric Encryption: RSA-1024 for key exchange
• Symmetric Encryption: AES-128-CBC for message content
• Key Management: Automatic generation and exchange of symmetric keys
• Message Integrity: End-to-end encryption ensures message authenticity

Security Considerations

• All messages are encrypted before transmission
• The server cannot decrypt the message content
• Each client pair uses unique symmetric keys
• Public keys are distributed through the server

📡 Communication Protocol

Message Flow

1. Key Exchange:

   • Client A requests Client B's public key
   • Client A sends a symmetric key request to Client B (encrypted with B's public key)
   • Client B responds with a symmetric key (encrypted with A's public key)

2. Message Exchange:

   • Messages are encrypted with a shared symmetric key
   • Server stores and forwards encrypted messages
   • Recipients decrypt messages using their symmetric key

Protocol Details

• Transport: TCP
• Encoding: Little-endian for numeric fields
• Message Types:
  • Symmetric key request (Type 1)
  • Symmetric key exchange (Type 2)
  • Text message (Type 3)
  • File transfer (Type 4 - bonus)

🗄️ Database Schema

Clients Table

Field	Type	Description
ID	16 bytes	Unique client identifier (UUID)
UserName	255 bytes	ASCII username string
PublicKey	160 bytes	Client's RSA public key
LastSeen	DateTime	Last client activity timestamp

Messages Table

Field	Type	Description
ID	4 bytes	Message ID
ToClient	16 bytes	Recipient client ID
FromClient	16 bytes	Sender client ID
Type	1 byte	Message type
Content	Blob	Encrypted message content

🏆 Bonus Features

• File Transfer (153): Send encrypted files between clients
• Persistent Storage: SQLite database for message and user persistence
• Enhanced Security: Additional security measures and protocol improvements

🧪 Testing

Development Guidelines

1. Modular Development: Implement components separately and test individually
2. Incremental Testing: Start with single client, then add multi-client support
3. Error Handling: Comprehensive exception handling throughout the system
4. Logging: Server-side logging for debugging and monitoring

Testing Scenarios

• Client registration and authentication
• Message sending and receiving
• Offline message delivery
• Key exchange mechanisms
• File transfer (bonus feature)
• Error handling and recovery

🚨 Error Handling

• Client-side: User-friendly error messages and graceful degradation
• Server-side: Proper error codes and logging
• Network: Connection timeout and retry mechanisms
• Encryption: Key validation and error recovery

📝 Development Notes

Code Quality Standards

• Object-Oriented Design: Use inheritance, encapsulation, and polymorphism
• Documentation: Comprehensive code comments and documentation
• Memory Management: Proper resource allocation and cleanup
• Security: Input validation and secure coding practices

Performance Considerations

• Memory Usage: Efficient handling of large messages and files
• Network Optimization: Minimal protocol overhead
• Database Optimization: Efficient query design and indexing

📚 Dependencies

Server (Python)

• Standard library modules only
• struct for binary data handling
• socket for network communication
• sqlite3 for database operations
• threading for concurrent client handling

Client (C++)

• STL (Standard Template Library)
• Crypto++ library for encryption
• Winsock or Boost for networking
• C++11 features (auto, lambda functions, etc.)

🤝 Contributing

This is an academic project. Please ensure:

• No external code-sharing or collaboration
• Use only approved libraries and resources
• Follow the specified development guidelines
• Maintain academic integrity standards

📄 License

This project is developed as part of an academic assignment for the Defensive Systems Programming course. All rights reserved.

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Assignment Details:

• Course: Defensive Systems Programming
• Assignment 15
• Semester: 2025A

Note: This implementation is designed for educational purposes and demonstrates secure communication protocols, encryption techniques, and network programming concepts.