Vigenere Cipher Decryption Tool

Overview

The Vigenere Cipher Decryption Tool is a Python-based application that allows users to decrypt text encrypted using the Vigenere cipher. The tool leverages a graphical user interface (GUI) built with Tkinter to make it user-friendly. The decryption process is enhanced with various algorithms to determine the probable key length and optimize the decryption key based on the letter frequencies in different languages.

Detailed Explanation of Code

1. DecryptionApp Class

The DecryptionApp class represents the main GUI application. It handles user interactions, file selection, and controls the decryption process.

• Initialization (__init__ method):
  Sets up the initial configuration of the application, including the window size, title, and background color. Initializes different screens, such as the welcome screen, file selection screen, and decryption screen.

• GUI Components:

  • self.welcome_screen: A frame displayed at the start, containing a welcome message and a "Start" button to initiate the decryption process.
  • self.file_selection_frame: A hidden frame initially, used for selecting the encrypted file.
  • self.select_file_btn: A button to open a file dialog for selecting a file to decrypt.

• Method Descriptions:

  • add_hover_effect & animate_button_hover: Adds visual feedback (color change) when hovering over buttons.
  • show_file_selection_screen: Hides the welcome screen and displays the file selection screen.
  • select_file: Opens a file dialog to allow the user to select a file. If decryption is in progress, it shows a warning.
  • confirm_decryption_start: Asks the user whether to start decryption immediately after a file is loaded.
  • ask_for_next_action: Prompts the user to choose between selecting another file or exiting the program.
  • start_decryption_thread: Initializes and starts a new thread for the decryption process to keep the GUI responsive.
  • decrypt_text_thread: Handles the decryption process in a separate thread to avoid blocking the main thread.
  • show_decryption_screen: Displays the main decryption screen with options to change the key, choose another file, or exit.
  • toggle_change_key: Shows or hides the panel that allows the user to change the decryption key manually.
  • display_file_content: Updates the GUI with the content of the decrypted file and key information.
  • select_new_file: Allows the user to select a new file for decryption.
  • prompt_save_before_action: Asks the user if they want to save the decrypted content before performing another action.
  • exit_program: Saves the current decryption and exits the application.
  • update_gui_callback & _update_gui_safe: Updates the GUI with messages or status changes from the decryption process.

2. Decryptor Class

The Decryptor class is responsible for the core logic of decrypting a Vigenere cipher. It determines the probable language of the text, calculates the key length, and optimizes the key for decryption.

• Initialization (__init__ method):
  Loads the encrypted text from the selected file, initializes language data, and prepares for decryption.

• Main Methods:

  • decrypt_text: The main method that determines the probable language of the text and attempts to decrypt it using different strategies.
  • decrypt_text_language_discovered: Continues the decryption process once the probable language and key length are determined.
  • handle_decryption_process: Manages the decryption process, updates the GUI, and allows user interaction for changing the key.
  • replace_letter_in_key: Allows manual replacement of letters in the decryption key.
  • frequency_generator: Generates all possible permutations of the top N most frequent letters for frequency analysis.

3. VigenereCipher Class

The VigenereCipher class handles the core decryption algorithm of the Vigenere cipher. It provides methods for decrypting text using a given key, optimizing the key based on letter frequency, and calculating shifts for different letters.

• Initialization (__init__ method):
  Validates the provided key and initializes the cipher.

• Core Methods:

  • decrypt: Decrypts the given text using the Vigenere cipher with the current key.
  • extract_segments: Extracts segments of the text based on the key length.
  • calculate_optimized_key_quick: Quickly calculates an optimized key for the cipher using the most frequent letters.
  • calculate_optimized_key: Calculates a more precise key using letter frequencies and chi-square analysis.

4. LanguageHelper Class

The LanguageHelper class provides helper methods for analyzing letter frequencies and determining the language of the text. It calculates the frequency of letters, the modified chi-square statistic, and the Index of Coincidence (IC) for language analysis.

How to Execute

Prerequisites

• Python 3.7 or higher
• Required libraries:
  • tkinter (comes pre-installed with Python)
  • threading
  • itertools
  • multiprocessing
  • collections

Installation

1. Clone the Repository:

   git clone https://github.com/your-repo/vigenere-decryption-tool.git
   cd vigenere-decryption-tool

2. Run the Application:

   Execute the following command in your terminal or command prompt:

   python main.py

Usage

1. Launch the Tool:
   After running the application, you will see a welcome screen.

2. Start the Decryption Process:
   Click the "Start" button to begin.

3. Select an Encrypted File:
   Choose the file you want to decrypt using the "Select File" button.

4. Confirm Decryption:
   Confirm that you want to start the decryption process.

5. Change Key (Optional):
   If needed, change the decryption key using the "Change Key" button.

6. Save Results:
   Save the decrypted file when prompted.

7. Exit the Tool:
   Click "Exit" to close the application.