Hacking Monoalphabetic Cipher

In this chapter, you will learn about monoalphabetic cipher and its hacking using Python.

Monoalphabetic Cipher

A Monoalphabetic cipher uses a fixed substitution for encrypting the entire message. A monoalphabetic cipher using a Python dictionary with JSON objects is shown here −

monoalpha_cipher = {
    a :  m ,
    b :  n ,
    c :  b ,
    d :  v ,
    e :  c ,
    f :  x ,
    g :  z ,
    h :  a ,
    i :  s ,
    j :  d ,
    k :  f ,
    l :  g ,
    m :  h ,
    n :  j ,
    o :  k ,
    p :  l ,
    q :  p ,
    r :  o ,
    s :  i ,
    t :  u ,
    u :  y ,
    v :  t ,
    w :  r ,
    x :  e ,
    y :  w ,
    z :  q ,
	   :    ,
}

With help of this dictionary, we can encrypt the letters with the associated letters as values in JSON object. The following program creates a monoalphabetic program as a class representation which includes all the functions of encryption and decryption.

from string import letters, digits
from random import shuffle

def random_monoalpha_cipher(pool = None):
   if pool is None:
      pool = letters + digits
   original_pool = pst(pool)
   shuffled_pool = pst(pool)
   shuffle(shuffled_pool)
   return dict(zip(original_pool, shuffled_pool))

def inverse_monoalpha_cipher(monoalpha_cipher):
   inverse_monoalpha = {}
   for key, value in monoalpha_cipher.iteritems():
      inverse_monoalpha[value] = key
   return inverse_monoalpha

def encrypt_with_monoalpha(message, monoalpha_cipher):
   encrypted_message = []
   for letter in message:
      encrypted_message.append(monoalpha_cipher.get(letter, letter))
   return   .join(encrypted_message)

def decrypt_with_monoalpha(encrypted_message, monoalpha_cipher):
   return encrypt_with_monoalpha(
      encrypted_message,
      inverse_monoalpha_cipher(monoalpha_cipher)
   )

This file is called later to implement the encryption and decryption process of Monoalphabetic cipher which is mentioned as below −

import monoalphabeticCipher as mc

cipher = mc.random_monoalpha_cipher()
print(cipher)
encrypted = mc.encrypt_with_monoalpha( Hello all you hackers out there! , cipher)
decrypted = mc.decrypt_with_monoalpha( sXGGt SGG Nt0 HSrLXFC t0U UHXFX! , cipher)

print(encrypted)
print(decrypted)

Output

You can observe the following output when you implement the code given above −

Thus, you can hack a monoalphabetic cipher with specified key value pair which cracks the cipher text to actual plain text.