simple_substitution.py

"""
This is an implementation of a simple substitution cipher.

This cipher involves replacing each letter of the alphabet uniquely with another letter in the alphabet.

It can also be broken using `frequency analysis`.
"""
from random import sample
from typing import Dict


class SimpleSubstitution_Cipher:

    """
    Steps
        1. Generate a random sequence of letters whereby each letter occurs once
        2. Map this sequence to an ordered sequence of letters in the alphabet. E.g [a, b, c] = [y, x, w] = [(a,y), (b,x), (c,w)]
    """

    letters = [
        "a",
        "b",
        "c",
        "d",
        "e",
        "f",
        "g",
        "h",
        "i",
        "j",
        "k",
        "l",
        "m",
        "n",
        "o",
        "p",
        "q",
        "r",
        "s",
        "t",
        "u",
        "v",
        "w",
        "x",
        "y",
        "z"]

    def generate_random_letters(self) -> list[str]:
        random_numbers = sample(range(0, 26), 26)
        letters: list[str] = []
        for i in random_numbers:
            letters.append(self.letters[i])
        return letters

    def assign(self, random_letters: list[str]) -> Dict[str, str]:
        letter_mapping: Dict[str, str] = {}
        for (i, v) in zip(self.letters, random_letters):
            letter_mapping[i] = v
        return letter_mapping

    def encrypt(self, word: str, letter_mapping: Dict[str, str]) -> str:
        new_word = ''
        for letter in word:
            new_word += letter_mapping[letter]
        return new_word

    def decrypt(self, word: str, letter_mapping: Dict[str, str]) -> str:
        reverse_mapping: Dict[str, str] = {}
        for (
                value,
                key) in zip(
                letter_mapping.values(),
                letter_mapping.keys()):
            reverse_mapping[value] = key
        new_word = ''
        for letter in word:
            new_word += reverse_mapping[letter]
        return new_word