MessageApp

A secure client-server messaging application using asymmetric and symmetric encryption.

Table of Contents

• Introduction
• Features
• File Structure
• Installation
• Usage
  • Server Actions
  • Client Actions
• Secure Communication Process
• Protocol Specifications
  • Requests from Client to Server
  • Responses from Server
• Encryption Details
• Database Schema
• Diagrams
• License

Introduction

MessageApp is a client-server-based secure messaging system. It uses RSA (asymmetric encryption) for key exchange and AES-CBC (symmetric encryption) for encrypting messages. The system supports user registration, message exchange, and secure key exchange.

Features

• Secure client-server communication
• User registration with UUIDs
• Public key exchange for encrypted messaging
• Secure symmetric key generation and storage
• Message queueing and retrieval
• Supports text messages and file transfers

File Structure

/MessageApp
 -/src 
      -/client 
             -/src
               -/ include 
                  - AESWrapper.h
                  - RSAWrapper.h
                  - Client.h
                  - Helpers.h
                  - ProtocolManager.h
                  - User.h
               -/client
                  - client.cpp
                  - helpers.cpp
                  - protocolhandler.cpp
                  - user.cpp
               -/encryption
                  - AESWrapper.cpp
                  - RSAWrapper.cpp
      -/server
            - database.py
            - logger.py
            - request.py
            - response.py
            - server.py

Installation

1. Clone the Repository

git clone https://github.com/gwchar2/MessageApp.git
cd MessageApp

2. Ensure Python is Installed and Install Dependencies

• Check if Python is installed:

  python3 --version

  If Python is not installed, download and install it from python.org.

• Install required dependencies:

  python3 -m pip install --upgrade pip
  python3 -m pip install -r requirements.txt

3. Install Crypto++ Library

• Linux (Debian/Ubuntu):

  sudo apt install libcryptopp-dev

• MacOS:

  brew install cryptopp

• Windows:

  • Download and install Crypto++ from Crypto++ official site.

  • Ensure the include path is set correctly when compiling.

  • You might need to add a complete path to cryptopp folder under CXXFLAGS and LDFLAGS in the makefile or c_cpp_properties.json under "includePath"

    Example for makefile addition

    CXXFLAGS = -std=c++17 -Wall -g -mrdrnd -I src/client/include -I "C:/Users/some_path/cryptopp" 
    LDFLAGS = -L "C:/Users/some_path/cryptopp" -lcryptopp -static -lpthread -lws2_32 \

4. Ensure GCC is Installed and Compile the Client & Encryption Modules

• Check if GCC is installed:

  gcc --version

  If GCC is not installed, install it:

  • Linux (Debian/Ubuntu): sudo apt install build-essential
  • MacOS: brew install gcc
  • Windows: Install MinGW and add it to the system PATH.

• Compile the modules:

  make

5. Start the Server and Client

• Start the server:

  python3 src/server/server.py

• Start the client:

  ./client

Usage

Server Actions

1. Reads port from myport.info
2. Waits indefinitely for client requests
3. Responds to various client requests:
   • Sign up: Creates a new user with a UUID (if username does not exist).
   • Client list: Returns a list of registered users.
   • Send message: Stores a message in memory for retrieval.
   • Waiting messages: Delivers queued messages and deletes them after retrieval.

Client Actions

1. Reads server and port from server.info
2. Reads and stores username, UUID, and encryption key from me.info
3. Displays an interactive terminal interface for user actions

User Terminal Options

• Register User (Request 110) - Registers and saves UUID.
• Request User List (Request 120) - Fetches all users.
• Request Public Key (Request 130) - Fetches a specific user's public key.
• Request Waiting Messages (Request 140) - Fetches unread messages.
• Send Message (Request 150) - Sends a text message.
• Request Symmetric Key (Request 151) - Fetches stored symmetric key.
• Send Symmetric Key (Request 152) - Generates and sends a new symmetric key.
• Send a File (Request 153) - Send a specific user a specific file up to 4gb.

Secure Communication Process

1. Client B requests Client A’s public key from the server.
2. Client B sends a request to Client A (via the server) for a symmetric encryption key, encrypted using Client A’s public key.
3. The server stores the request for Client A to retrieve later.
4. Client A pulls the waiting request from the server.
5. Client A decrypts the request using its private key.
6. Client A requests Client B’s public key from the server.
7. Client A sends a response with the symmetric encryption key, encrypted with B’s public key.
8. The server stores the response for Client B to retrieve.
9. Client B pulls the response from the server.
10. Client B decrypts the symmetric key using its private key.
11. Both clients can now securely communicate using the shared symmetric key.

Protocol Specifications

Requests from Client to Server

Request Code	Description
600	Sign up
601	Get members list
602	Get a specific user's public key
603	Send a message
604	Pull waiting messages

Responses from Server

Response Code	Description
2100	Sign up successful
2101	Members list
2102	Public key
2103	Message stored
2104	All waiting messages
9000	General error

Encryption Details

• Symmetric Encryption: AES-CBC (128-bit key)
• Asymmetric Encryption: RSA (1024-bit key without header, 1280-bit with header)

Database Schema

For database setup, refer to database_schema.sql.

CREATE TABLE IF NOT EXISTS clients (
    ID BLOB(16) PRIMARY KEY,
    UserName VARCHAR(255) NOT NULL,
    PublicKey BLOB(160) NOT NULL,
    LastSeen DATETIME NOT NULL
);

CREATE TABLE IF NOT EXISTS messages (
    ID INTEGER PRIMARY KEY AUTOINCREMENT,
    ToClient BLOB(16) NOT NULL,
    FromClient BLOB(16) NOT NULL,
    Type TINYINT NOT NULL,
    Content BLOB,
    FOREIGN KEY (ToClient) REFERENCES clients(ID),
    FOREIGN KEY (FromClient) REFERENCES clients(ID)
);

Diagrams

Below are diagrams that illustrate the message exchange process:

Client A, Client B, and Server Communication Flow

End-to-End Encryption Process

License

This project is licensed under the MIT License.