🔒 Secure Communication System

Overview

Welcome to our Secure Communication System!
This project implements a robust, real-world inspired secure end-to-end encrypted messaging platform with three main modes:

• Client 🧑‍💻
• Server 🖥️
• Certificate Authority (CA) 🏛️

Our system uses modern cryptography standards to ensure confidentiality, authentication, and integrity for all communications.

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🚀 Features

• Three Modes:

  • Client: Connects to the server and CA, sends/receives secure messages and files.
  • Server: Handles secure communication with clients.
  • Certificate Authority: Issues and signs digital certificates.

• End-to-End Security:

  • RSA for certificate management and secure key exchange.
  • AES-256 (CTR mode) for fast and strong symmetric encryption.
  • HMAC-SHA256 for message authentication and integrity.
  • Custom Certificates inspired by X.509 (see our Certificate.java).

• Replay Attack Protection:

  • Uses nonces and sequence numbers to prevent replay attacks.

• Industry Standards:

  • Protocols and key derivation follow RFCs (e.g., RFC 5246, RFC 7627).

• Easy to Use:

  • Simple command-line interface.
  • Clear logs and error messages.

• Usage

  • Select the desired mode (Client, Server, CA) at startup. type 1 2,3 respectively.
  • Enter the required IP addresses for the server and CA.
  • Send the text messages with pressing Enter.
  • Send files by typing image:<path_to_file> or video:<path_to_file>.

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🛡️ Security Concepts

Feature	How We Achieve It
Confidentiality	AES-256 encryption for all messages and files.
Authentication	RSA-based certificates signed by the CA, verified before communication.
Integrity	HMAC-SHA256 ensures messages are not tampered with.
Replay Immunity	Nonces and sequence numbers prevent replay attacks.

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🛠️ Technologies & Concepts Used

• Java 17+
• RSA (2048 bits)
• AES-256 (CTR mode)
• HMAC-SHA256
• Custom Certificate Format (X.509-like)
• Sockets & Streams
• RFC 5246, RFC 7627 (TLS/SSL standards)

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📸 Screenshots

Client Mode	Server Mode	Certificate Authority

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⚡ How to Use

1. Compile the Project:

   javac -d bin src/*.java

2. Run in Desired Mode:

   # Start as Certificate Authority
   java -cp bin App
   # Select "3" for CA mode
   
   # Start as Server
   java -cp bin App
   # Select "2" for Server mode
   
   # Start as Client
   java -cp bin App
   # Select "1" for Client mode

3. Usage:
   Enter the required IP addresses for the server and CA.
   Send messages or files securely!

🤝 Credits

• Inspired by industry standards and RFCs.
• Designed and implemented by our team for CSE4057 Spring 2025.

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📄 License

This project is for educational purposes.