railfence_cipher_tool

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Filename: railfence_cipher_tool.py
# Version: 1.0.0
# Author: Jeoi Reqi

"""
Description:
    - This script provides a tool for encrypting and decrypting messages using the Rail Fence Cipher.
    - Additionally, it has the option to encrypt & decrypt a demo cipher using a quote by Margaret Thatcher.

Requirements:
    - Python 3.x
    - The following modules:
        - math
        - itertools

Functions:
    - main():
        The main function to run the program and interact with the user.
    - encrypt_message(plaintext):
        Encrypts a message using the Rail Fence Cipher.
    - prep_plaintext(plaintext):
        Removes spaces and converts the message to uppercase.
    - build_rails(message):
        Builds strings with every other letter in a message.
    - decrypt_message(ciphertext):
        Decrypts a message using the Rail Fence Cipher.
    - prep_ciphertext(ciphertext):
        Removes whitespace from the ciphertext.
    - split_rails(message):
        Splits the message into two parts for decryption.
    - decrypt(row1, row2):
        Builds the plaintext from two rows of ciphertext.
    - run_demo():
        Runs a demo with provided ciphertext.

Usage:
    - Run the script and follow the on-screen menu to encrypt or decrypt messages using the Rail Fence Cipher.

Additional Notes:
    - The Rail Fence Cipher is a transposition cipher that encrypts and decrypts messages by writing the characters in a zigzag pattern.
    - In the Rail Fence Cipher, the plaintext is written diagonally up and down in a zigzag pattern on successive "rails" of an imaginary fence, then read off row by row to produce the ciphertext.
"""

import math
import itertools

def main():
    """Run program."""
    while True:
        print("_" * 21)
        print("\nRailfence Cipher Menu")
        print("_" * 21, "\n")
        print("1. Run Demo")
        print("2. Encrypt a message")
        print("3. Decrypt a message")
        print("0. Exit")
        choice = input("\nEnter your choice: ")

        if choice == '1':
            run_demo()
        elif choice == '2':
            plaintext = input("Enter the plaintext to encrypt: ")
            print()
            encrypt_message(plaintext)
        elif choice == '3':
            ciphertext = input("Enter the ciphertext to decrypt: ")
            print()
            decrypt_message(ciphertext)
        elif choice == '0':
            print()
            print("_" * 21)
            print("\nExiting program...\n\n   👋     GoodBye!")
            print("_" * 21, "\n")
            break
        else:
            print("Invalid choice. Please enter 1, 2, 3, or 4.")

def encrypt_message(plaintext):
    """Encrypt a message using rail fence cipher."""
    message = prep_plaintext(plaintext)
    rails = build_rails(message)
    ciphertext = ' '.join([rails[i:i+5] for i in range(0, len(rails), 5)])
    print("ENCODED (Ciphertext):   {}".format(ciphertext))
    print("FORMATTED (Ciphertext): {}".format(ciphertext.replace(" ", "").lower()))

def prep_plaintext(plaintext):
    """Remove spaces & leading/trailing whitespace."""
    message = "".join(plaintext.split())
    message = message.upper()  # convention for ciphertext is uppercase
    return message

def build_rails(message):
    """Build strings with every other letter in a message."""
    evens = message[::2]
    odds = message[1::2]
    rails = evens + odds
    return rails

def decrypt_message(ciphertext):
    """Decrypt a message using rail fence cipher."""
    formatted_ciphertext = ciphertext.replace(" ", "")
    print("ENCODED (Formatted): ", formatted_ciphertext.lower())

    message = prep_ciphertext(ciphertext)
    row1, row2 = split_rails(message)
    decrypt(row1, row2)

def prep_ciphertext(ciphertext):
    """Remove whitespace."""
    message = "".join(ciphertext.split())
    return message

def split_rails(message):
    """Split message in two, always rounding UP for 1st row."""
    row_1_len = math.ceil(len(message)/2)
    row1 = (message[:row_1_len]).lower()
    row2 = (message[row_1_len:]).lower()
    return row1, row2

def decrypt(row1, row2):
    """Build list with every other letter in 2 strings & print."""
    plaintext = []
    for r1, r2 in itertools.zip_longest(row1, row2):
        plaintext.append(r1)
        plaintext.append(r2)
    if None in plaintext:
        plaintext.pop()
    print("DECODED (Plaintext):  {}".format(''.join(plaintext)))

def run_demo():
    """Run demo with provided ciphertext."""
    ciphertext = """YUNIO EYODR ALBTC NMSSR VLNNR SRCUE -AGRT HTHRO ADCMB RAORI ,UEOO ITTAE OIFAT UTR.M RAETA CE"""
    formatted_ciphertext = ciphertext.replace(" ", "")

    print("\nCIPHERTEXT: ", ciphertext, "\n")
    print("ENCODED (Formatted): ", formatted_ciphertext.lower())

    message = prep_ciphertext(ciphertext)
    row1, row2 = split_rails(message)
    decrypt(row1, row2)

if __name__ == '__main__':
    main()