fernet_cipher_tool

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Filename: fernet_cipher_tool.py
# Version: 1.1.0
# Author: Jeoi Reqi

"""
This script provides options to generate, delete, encrypt, and decrypt messages using the Fernet symmetric encryption algorithm.

Requirements:
    - Python 3.x
    - cryptography library

Functions:
    1. generate_key():
       - Generates a new Fernet key and saves it to a file.
    2. load_key():
       - Loads the Fernet key from the key file if it exists.
    3. delete_key():
       - Deletes the key file if it exists.
    4. encrypt_message(message, key):
       - Encrypts a message using the provided Fernet key.
    5. decrypt_message(encrypted_message, key):
       - Decrypts an encrypted message using the stored Fernet key.
    6. main():
       - Main function to run the Fernet Options Menu.

Usage:
    1. Run the script in a Python environment.
    2. Follow the on-screen prompts to perform various actions such as generating a key,
       encrypting a message, decrypting a message, and deleting the key.

Additional Notes:
    - The generated Fernet key is saved to a file named "key.txt" in the current working directory.
    - When encrypting or decrypting messages, the script automatically generates a key if none is found.
    - Users can delete the stored key if needed, and the script will inform if no key exists for deletion.
    - All input/output is done via the console, providing a user-friendly interface for interaction.
"""

import os
import base64
from cryptography.fernet import Fernet

# GENERATE KEY
def generate_key():
    """
    Generate a new Fernet key and save it to a file.

    Returns:
        bytes: The generated Fernet key.
    """
    key = Fernet.generate_key()
    with open("key.txt", "wb") as key_file:
        key_file.write(key)
    return key

# LOAD STORED KEY FROM FILE
def load_key():
    """
    Load the Fernet key from the key file if it exists.

    Returns:
        bytes: The loaded Fernet key if exists, otherwise None.
    """
    if os.path.exists("key.txt"):
        with open("key.txt", "rb") as key_file:
            return key_file.read()
    else:
        print("\nNo saved key found!\n- Generating a new 32-byte Fernet key...")
        return generate_key()

# DELETE STORED KEY
def delete_key():
    """
    Delete the key file if it exists.
    """
    if os.path.exists("key.txt"):
        os.remove("key.txt")
        print("\nKey deleted!")
    else:
        print("\nNo key to delete!")

# ENCRYPTION FUNCTION
def encrypt_message(message, key):
    """
    Encrypt a message using the provided Fernet key.

    Args:
        message (str): The message to encrypt.
        key (bytes): The Fernet key used for encryption.

    Returns:
        bytes: The encrypted message.
    """
    fernet = Fernet(key)
    print(f"\nEncoding using the stored key:\n- {key.decode()}")
    return fernet.encrypt(message.encode())

# DECRYPTION FUNCTION
def decrypt_message(encrypted_message, key):
    """
    Decrypt an encrypted message using the provided Fernet key.

    Args:
        encrypted_message (bytes): The encrypted message to decrypt.
        key (bytes): The Fernet key used for decryption.

    Returns:
        str: The decrypted message.
    """
    fernet = Fernet(key)
    print(f"\nDecoding using the stored key:\n- {key.decode()}")
    return fernet.decrypt(encrypted_message).decode()

# MAIN MENU
def main():
    """
    Main function to run the Fernet Options Menu.
    """
    while True:
        print("\n" + "*" * 50)
        print("\t  :: Fernet Options Menu ::")
        print("*" * 50 + "\n")
        print("\t   1. \tGenerate Key")
        print("\t   2. \tDelete Key")
        print("\t   3. \tEncrypt Message")
        print("\t   4. \tDecrypt Message")
        print("\t   5. \tExit Program\n")
        print("*" * 50)
        choice = input("Enter your choice (1-4) or... 5 to EXIT: ")

        if choice == "1":
            key = generate_key()
            print("\nGenerated Key:", key.decode())
        elif choice == "2":
            delete_key()
        elif choice == "3":
            message = input("\nEnter the message to encrypt: ")
            key = load_key()
            encrypted_message = encrypt_message(message, key)
            print("\nEncrypted Message:", encrypted_message.decode())
        elif choice == "4":
            encrypted_message = input("\nEnter the encrypted message: ")
            key = load_key()
            decrypted_message = decrypt_message(encrypted_message.encode(), key)
            print("\nDecrypted Message:", decrypted_message)
        elif choice == "5":
            print("\nExiting Program...\tGoodbye!\n")
            break
        else:
            print("\nInvalid choice! Please enter 1, 2, 3, 4, or 5.\n")

if __name__ == "__main__":
    main()