1.6 Brute Force

Exercise 1.6 Brute Force

Try having your cryptogram-decoding program brute force a message. How long would it take to test every possible mapping? Can you write a program that can speed this up with any kind of “smart guess”?

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Possible brute force code:

# ex1_6.py

import ex1_5

def bruteforce(ciphertext: str): 
    for possible_key in range(31469973260387937525653122354950764088012280797258232192163168247821107200000000000000):
        possible_plaintext = ex1_5.decryptUsingIndex(ciphertext=ciphertext, key=possible_key)
        x = input(f"Is this the plaintext you are looking for [{possible_plaintext}] 🤣 [Y][N]:")
        if x == 'Y': 
            # we found the plain text we are looking for hooray
            return 

bruteforce("hellF PFSld hFP ZHR IOK NOVmw bq NZ7Z0D")

Running the code:

As you can imagine this will take an awful amount of time.

Not only that, we can even have “fake plaintexts”. That is plaintext that the attacker thinks is correct but was not the actual plaintext that was sent. This arises when the attacker decrypts the ciphertext with a wrong key and by coincidence the incorrect plaintext contains english words luring the attacker into believing he has found the correct key (even though he didn’t).

The cryptanalysis method Frequency analysis seems to be effective against such ciphers.