Krypto_Grundlagen/chapter_two/Homophone_Chiffre.py

import math
import random

from utils import AlphabetUtils as au
from utils import CipherUtils as cu


def encrypt_text(cleartext: str, key: {}) -> str:
	"""
	Encrypts the given text with the given key
	:param cleartext: The text to encrypt
	:param key: The key to use. Has to be generated with the function below in order to work properly.
	:return: The encrypted text
	"""
	cleartext = cu.transform_invalid_chars(cleartext)

	letter_length = key['config']['letter_length']

	resulting = ''

	for char in cleartext:
		possible_ciphers = key['data'][char.lower()]
		chosen_cipher = random.choice(possible_ciphers)
		resulting += str(chosen_cipher).zfill(letter_length)

	return resulting


def decrypt_text(ciphertext: str, key: {}) -> str:
	"""
	Decrypts the given ciphertext with the given key
	:param ciphertext: The text to decrypt
	:param key: The key to use. Has to be generated with the function below in order to work properly.
	:return: The decrypted text
	"""
	letter_length = key['config']['letter_length']

	letter_split = [ciphertext[i:i + letter_length] for i in range(0, len(ciphertext), letter_length)]

	transformed_key = _transform_key(key)

	resulting = ''

	for cipher_letter in letter_split:
		cleartext = transformed_key[int(cipher_letter)]
		resulting += str(cleartext)

	return resulting


def _transform_key(key: {}) -> []:
	"""
	Transforms the given key into a format that can be easier used for decryption
	:param key: The key to transform
	:return: The transformed key. Contains a list where the index is the ciphertext and the value is the cleartext
	"""
	transformed_key = [None] * int(key['config']['max_cipher'])

	for letter in key['data'].keys():
		possible_ciphers = key['data'][letter]
		for cipher in possible_ciphers:
			transformed_key[int(cipher)] = letter

	return transformed_key


def generate_key(key_distribution: [int]) -> {}:
	"""
	Generates a key that can be used for this cipher by using the given key distribution profile
	:param key_distribution: The key distribution, e.g. number of possibilities per letter
	:return: The key as an object which contains the letter as key and the list of possible ciphers as value
	"""
	key = {
		'config': {},
		'data': {}
	}

	# Generate the key possibilities
	amount_of_numbers = sum(key_distribution)
	key_possibilities = [i for i in range(amount_of_numbers)]
	random.shuffle(key_possibilities)

	# Because the ciphertext does not contain of letters but of numbers instead and these are dependent on the key,
	# we need to include the fixed length of each 'letter' here
	key['config']['letter_length'] = len(str(amount_of_numbers))
	key['config']['max_cipher'] = str(amount_of_numbers)

	# Distribute the keys to the letters
	for letter_index in range(len(key_distribution)):
		letter = au.get_letter_at_index(letter_index)

		keys_for_this_letter = []

		for key_possibility in range(key_distribution[letter_index]):
			keys_for_this_letter.append(key_possibilities.pop())

		key['data'][letter] = keys_for_this_letter

	return key


def generate_key_distribution(base: str, multiplier: int) -> [int]:
	"""
	Generates a key distribution profile based on the letter frequencies of the given input text.
	Larger inputs generally result in better key distribution profiles.
	:param base: The text to use as a sort of seed
	:param multiplier: A multiplier for the possibilities per letter
	:return: The key distribution profile as a list of integers
	"""
	letter_distribution = cu.calculate_frequency(base)

	return [math.ceil(i * 100 * multiplier) for i in letter_distribution]


def get_german_key_distribution(multiplier: int) -> [int]:
	"""
	Returns the 'optimal' key distribution profile for german texts
	:param multiplier: A multiplier for the possibilities per letter
	:return: The key distribution profile as a list of integers
	"""
	return [math.ceil(i * 100 * multiplier) for i in cu.GERMAN_FREQUENCY_PROFILE]


if __name__ == '__main__':
	dist = get_german_key_distribution(10)
	print(dist)
	key = generate_key(key_distribution=dist)
	print(key)
	ciphertext = encrypt_text('BonkRocks', key)
	print(ciphertext)
	print(decrypt_text(ciphertext, key))