Security and Cryptography in Python - Substitution Cipher

Security and Cryptography in Python - Substitution Cipher

A Substitution Cipher has

\[26! = 403291461126605635584000000 \]

possible permutations / possible keys.

\[26! = 403291461126605635584000000 \]

\[2^88 = 309485009821345068724781056 \]

Hence a 88 bit security.

Encryption

import random

def generate_key():
    letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    cletters = list(letters)
    key = {}
    for c in letters:
        key[c] = cletters.pop(random.randint(0,len(cletters) - 1))
    return key

key = generate_key()
print(key)

First Running Result:

Second Running Result:

import random

def generate_key():
    letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    cletters = list(letters)
    key = {}
    for c in letters:
        key[c] = cletters.pop(random.randint(0,len(cletters) - 1))
    return key

def encrypt(key, message):
    cipher = ""
    for c in message:
        if c in key:
            cipher += key[c]
        else:
            cipher += c
    return cipher

key = generate_key()
print(key)
message = "YOU ARE AWESOME"
cipher = encrypt(key, message)
print(cipher)

First Running Result:

Second Running Result:

Decryption

import random

def generate_key():
    letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    cletters = list(letters)
    key = {}
    for c in letters:
        key[c] = cletters.pop(random.randint(0,len(cletters) - 1))
    return key

def encrypt(key, message):
    cipher = ""
    for c in message:
        if c in key:
            cipher += key[c]
        else:
            cipher += c
    return cipher

def get_decrypt_key(key):
    dkey = {}
    for k in key:
        dkey[key[k]] = k
    return dkey

key = generate_key()
print(key)
message = "YOU ARE AWESOME"
cipher = encrypt(key, message)
print(cipher)
dkey = get_decrypt_key(key)
message = encrypt(dkey, cipher)
print(message)

First Running Result:

Second Running Result: