🔐 Secure Instant Messaging System

This project was developed as part of CY6740: Network Security at Northeastern University. It demonstrates a secure, terminal-based chat system built using modern cryptographic techniques in Python.

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Overview

The application enables secure communication between users by integrating:

• SRP (Secure Remote Password protocol) for password-based authentication
• ECDH (Elliptic Curve Diffie-Hellman) for key exchange
• AES-GCM (Galois/Counter Mode) for message confidentiality and integrity
• A socket-based client-server model with encrypted peer-to-peer messaging

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Features

• Secure login (SRP - no password transmission)
• Encrypted messaging (ECDH key exchange + AES-GCM)
• Real-time chat via TCP sockets
• Online user listing
• Message rate limiting (5 messages per 10 seconds)
• Simple command-based interface

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Test Users

You can log in using the following credentials (preloaded in server.py):

Username	Password
alice	@lice_$
bob	B0b@#redS0x
charlie	ilovechristmas

These users have SRP verifiers already defined in the server logic.

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🛠️ Setup Instructions

1. Clone the Repository

git clone https://github.com/Samyukta-14/secure-chat-application.git
cd secure-chat-application

2. Install Dependencies

pip install -r requirements.txt

How to Run

Start the Server

python src/server.py

Start the Client

python src/client.py

Then log in with one of the test usernames above.

⌨️ Client Commands

Commands	Description
connect	Initiate secure chat with another user
accept	Accept a chat request from another user
send	Send an encrypted message in current chat
back	Exit the current chat session
list	List all online users
logout	Logout from the server
quit	Exit the client application

⚠️ You must connect/accept before sending messages.

Security Details

• Authentication: Uses SRP
• Key Exchange: ECDH
• Encryption: AES-256 in GCM mode
• Session Keys: Derived from ECDH using HKDF (SHA256)
• Rate Limiting: Limits users to 5 messages per 10 seconds

All cryptographic operations are performed using standard libraries.

File Structure

secure-chat-application/
├── src/
│   ├── client.py
│   └── server.py
├── config/
│   └── config.txt
├── scripts/
│   └── salt-verifier-generator.py
├── requirements.txt
├── README.md
├── .gitignore
└── LICENSE

👥 Contributors

• Samyukta Kurikala (https://github.com/Samyukta-14)
• Tanmay Sharma (https://github.com/d3adp0et)