securecli

securecli is a lightweight command-line chat application that uses the Diffie-Hellman key exchange to establish a shared secret between two peers. All messages are encrypted using a simple XOR cipher with a key derived from the shared secret.

⚠️ Note: This project is intended for learning purposes. It uses small primes and a basic XOR cipher for demonstration. Do not use this in production.

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Features

• Pure Python — no external dependencies
• Works in server or client mode
• Diffie-Hellman key exchange for secure key agreement
• Symmetric encryption using a derived shared secret
• Interactive real-time chat over TCP

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How It Works

1. Key Exchange

   • Server and client each generate a private key.
   • Public keys are computed using Diffie-Hellman and exchanged over the network.
   • Both parties compute the same shared secret without sending it directly.

2. Encryption

   • The shared secret is hashed with SHA-256 to create a symmetric key.
   • Messages are encrypted and decrypted using a simple XOR cipher with the key.

3. Communication

   • Messages are sent over a TCP connection and decrypted on the other side.

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Requirements

• Python 3.7 or higher
• No external libraries required

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Installation

Clone this repository:

git clone https://github.com/noahwhlim/securecli.git
cd securecli

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Starting the App

1. Start the Server

Open a terminal and run:

python main.py server <port>

Replace <port> with the port number you want the server to listen on (e.g., 5000).

Example:

python main.py server 5000

2. Start the Client

Open another terminal and run:

python main.py client <server_host> <port>

Replace <server_host> with the server's IP address (127.0.0.1 if local) and <port> with the same port the server is listening on.

Example:

python main.py client 127.0.0.1 5000

3. Chat

• Type your messages and press Enter to send.
• Type /quit to exit the chat.

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Example

Server Terminal

Server listening on port 5000...
Connected by ('127.0.0.1', 60312)
Shared key established: 2
Client: Hello from client!
You: Hi there!

Client Terminal

Shared key established: 2
You: Hello from client!
Server: Hi there!

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Security Notes

• This demo uses a very small prime for simplicity.

• XOR encryption is not secure for real-world use.

• In a production-ready version, you would:

  • Use a large prime and generator for Diffie-Hellman.
  • Replace XOR with AES or ChaCha20.
  • Implement proper authentication and replay attack prevention.

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License

MIT License — feel free to use and modify.