atbash.md

Atbash is a simple substitution cipher possible with any known alphabet. It emerged around 500-600 BCE. It works by substituting the letters of an alphabet with another.

Assumptions

CONSTANT = 'abcdefghijklmnopqrstuvwxyz'

A random shuffle of the constant is the cipher.

Example cipher: zyxwvutsrqponmlkjihgfedcba

Using the cipher, strings can be encrypted. When the cipher and encrypted string is given it is possible to decrypt the encrypted text.

To run: python atbash_test.py

This will run the atbash.py and print the decoded message

Requires python3

atbash.py

CONSTANT = 'abcdefghijklmnopqrstuvwxyz'

def buildDecoder(cipher):
#builds a dictionary to decrypt the code using the cipher - uses dictionary comprehension
    dictionary = {cipher[i] : CONSTANT[i] for i in range(len(CONSTANT))}
    return dictionary

def decrypt(text, cipher):
#loops over the string and matches each char with its true value
    cipher_dict = buildDecoder(cipher)

    decrypted_text = "";
    for char in text:
        if char in cipher_dict:
            decrypted_text += cipher_dict[char]
        else:
            decrypted_text += char

    print(decrypted_text)
    return decrypted_text

atbash_test.py

import unittest

from atbash import buildDecoder, decrypt

class AtbashTest(unittest.TestCase):

    def test_decrypt(self):
        self.assertEqual("houston, we have a problem", decrypt("knlfgnb, sj koqj o yvnewju", "oephjizkxdawubnytvfglqsrcm"))

    def test_numbers_and_special(self):
        self.assertEqual("1337 why so serious?", decrypt("1337 skd qj qucbjvq?", "xipmuzfkbrlwotjancqgveshdy"))

    def test_decrypt_short(self):
        self.assertEqual("car", decrypt("dzs", "zodvqukgwefbyitmrsplhacxnj"))

    def test_decrypt_fail(self):
        self.assertNotEqual("why so unserious?", decrypt("sdf so serious","xipmuzfkbrlwotjancqgveshdy"))


if __name__ == '__main__':
    unittest.main()