230 http://inventwithpython.com/hacking

Email questions to the author: [email protected]

The Affine Cipher Hacking Function

affineHacker.py

25. def hackAffine(message):


26. print('Hacking...')


27. 
    


28. 
    

    Python programs can be stopped at any time by pressing Ctrl-C (on

    
    


29. 
    

    Windows) or Ctrl-D (on Mac and Linux)

    
    


30. print('(Press Ctrl-C or Ctrl-D to quit at any time.)')

The hackAffine() function has the code that does the decryption. This can take a while, so if
the user wants to exit the program early, she can press Ctrl-C (on Windows) or Ctrl-D (on OS X
and Linux).

The ** Exponent Operator

There is another math operator besides the basic +, -, *, /, and // operators. The ** operator is

Python’s exponent operator. This does “to the power of” math on two numbers. For example,
“two to the power of five” would be 2 5 in Python code. This is equivalent to two
multiplied by itself five times: 2 2 2 2 2. Both the expressions 2 5 and 2
2 2 2 2 evaluate to the integer 32.

Try typing the following into the interactive shell:

2 6
64
42
16
24
16
12310
792594609605189126649

affineHacker.py

32. 
    

    brute-force by looping through every possible key

    
    


33. for key in range(len(affineCipher.SYMBOLS) ** 2):


34. keyA = affineCipher.getKeyParts(key)[0]

The range of integers for the keys used to brute-force the ciphertext will range from 0 to the size
of the symbol set to the second power. The expression:

len(affineCipher.SYMBOLS) ** 2