Encrypted Chat TCP/UDP

Description

This project is a secure, distributed chat application that demonstrates network communication using both TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). It prioritizes security by implementing RSA cryptography to ensure message confidentiality and digital signatures to verify the authenticity of the senders.

Technologies

• Java SE (Socket and DatagramSocket API)
• RSA Cryptography (2048-bit keys)
• Digital Signatures (SHA256withRSA)
• TCP/IP & UDP Protocols

Features

• Dual Protocol Support: Includes independent implementations for both TCP and UDP communication.
• End-to-End Encryption: Uses RSA public keys to encrypt private messages, ensuring only the intended recipient can read them.
• Identity Verification: Employs digital signatures to prevent message tampering and impersonation.
• Multi-Client Handling: The servers manage multiple simultaneous connections and maintain a registry of active users and their public keys.
• Command System: Built-in commands for listing active users (!list) and exiting the chat (!exit).

How to Run

1. Compile the Project

Navigate to the src directory and compile all Java files:

javac *.java

2. Start the Server

Run either the TCP or UDP server version:

• TCP: java ChatServerTCP
• UDP: java ChatServerUDP

3. Run the Clients

Open multiple terminal windows to simulate different users and run:

• TCP: java ChatClientTCP
• UDP: java ChatClientUDP

4. Chatting Securely

• Global Message: Just type your message and press Enter.
• Private Message: Use @username message.
• Encrypted/Signed Private Message: Use @username SECURE message.

Project Structure

• ChatServerTCP.java & ChatServerUDP.java: Manage client connections, coordinate message broadcasting, and store public keys.
• ChatClientTCP.java & ChatClientUDP.java: Handle user input, key generation, and the asynchronous receiving of messages.
• RSAUtils.java: A utility class containing the logic for generating 2048-bit RSA keys, encrypting/decrypting data, and signing/verifying messages.
• .gitignore: Configured to ignore compiled .class files and IDE-specific folders.
• README.md: Project documentation.

What I Learned

• Network Fundamentals: Differences between stream-oriented (TCP) and packet-oriented (UDP) communication in a real-world application.
• Asymmetric Cryptography: Practical implementation of RSA for secure key exchange and data protection.
• Concurrency: Using Java Threads to handle simultaneous I/O operations without blocking the user interface.
• Data Serialization: Encoding binary keys and encrypted data into Base64 strings for safe transmission over text-based protocols.

Future Improvements

• Key Persistence: Store public keys in a database or file instead of volatile memory.
• GUI: Develop a graphical user interface to replace the current command-line interface.
• Hybrid Encryption: Implement AES for message encryption and use RSA only for exchanging the AES session keys to improve performance for large messages.