Shift Cipher

shift_cipher.py

import string


class ShiftCipher:
    def __init__(self, shift_size=3):
        self.shift_size = shift_size % 26
        self.shifted = []
        for decrypted in string.ascii_uppercase:
            encrypted = chr((ord(decrypted) - ord('A') + self.shift_size) % 26 + ord('A'))
            self.shifted.append(encrypted)

    def encrypt(self, plain_text):
        plain_text = plain_text.upper()
        cipher_text = [self.shifted[string.ascii_uppercase.index(p)] for p in plain_text]
        cipher_text = ''.join(cipher_text)
        return cipher_text

    def decrypt(self, cipher_text):
        cipher_text = cipher_text.upper()
        plain_text = [string.ascii_uppercase[self.shifted.index(c)] for c in cipher_text]
        plain_text = ''.join(plain_text)
        return plain_text

    @staticmethod
    def crack(ciphertext, plain_text):
        for shift_size in range(26):
            shift_cipher = ShiftCipher(shift_size)
            decrypted_text = shift_cipher.decrypt(ciphertext)
            if decrypted_text == plain_text:
                return shift_size
        return None