MessageU

MessageU is a secure client–server messaging system developed as part of an advanced defensive programming course.

Overview

• Client: C++ (Visual Studio 2019, Windows)
• Server: Python (TCP socket server), concurrent requests handling
• Protocol: Custom binary (Little Endian) with fixed-size header + variable payload (see protocol folder)
• Encryption: RSA (asymmetric) + AES-CBC (symmetric)
• Design: Stateless server; each client reconnects per request

Features

• User registration and UUID persistence
• Public key exchange between clients
• Encrypted text messaging (end-to-end)
• Server-side message queue for offline delivery
• Robust error handling and security-focused protocol logic

Runtime Notes

Two small configuration files are required for runtime (not included in submission):

• Client side: data/server.info

  <server_ip> <port>
  

  Example:

  127.0.0.1:1357
  

• Server side: myport.info

  <port>
  

  Example:

  1357
  

The client reads its file from the data subfolder, and the server expects its file in the same directory as server.py.

Build (Client)

Open x64 Native Tools Command Prompt for VS 2019 and run:

cd client
cl /EHsc /MD /std:c++17 /Fe:MessageUClient.exe *.cpp /I . ^
   /I "C:\vcpkg\installed\x64-windows\include" ^
   /link "C:\vcpkg\installed\x64-windows\lib\cryptopp.lib"

Requires Crypto++ installed via vcpkg:
vcpkg install cryptopp:x64-windows

▶️ Run

MessageUClient.exe

Expected startup message:

MessageU client at your service.

Future Improvements

Security

• Replace static IV in AES-CBC with random IV per message.
• Switch from AES-CBC to AES-GCM or another authenticated encryption mode for integrity protection.
• Upgrade to RSA-2048 and verify key authenticity to prevent impersonation.
• Add forward secrecy using ephemeral key exchange (e.g., Diffie–Hellman).
• Wrap communication with TLS to prevent active network attacks.

Design

• Persist registered users and queued messages in a database (e.g., SQLite).
• Improve protocol versioning and error reporting.
• Extend client interface with message history and file attachments.
• Add automated integration and encryption tests.

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This project was created for academic purposes, demonstrating secure communication design, encryption integration, and defensive coding practices.