From: Neil Smith <neil.git@njae.me.uk>
Date: Mon, 14 Jul 2014 19:04:52 +0000 (+0100)
Subject: Breaking keyword ciphers
X-Git-Url: https://git.njae.me.uk/?a=commitdiff_plain;h=4795449c28e74b011ea907a1c2620cf037574c9f;p=cipher-training.git

Breaking keyword ciphers
---

diff --git a/cipher.py b/cipher.py
index d2438b7..c5e3938 100644
--- a/cipher.py
+++ b/cipher.py
@@ -309,30 +309,6 @@ def keyword_decipher(message, keyword,
     return message.lower().translate(cipher_translation)
 
 
-def vigenere_encipher(message, keyword):
-    """Vigenere encipher
-
-    >>> vigenere_encipher('hello', 'abc')
-    'hfnlp'
-    """
-    shifts = [ord(l) - ord('a') for l in sanitise(keyword)]
-    pairs = zip(message, cycle(shifts))
-    return ''.join([caesar_encipher_letter(l, k) for l, k in pairs])
-
-def vigenere_decipher(message, keyword):
-    """Vigenere decipher
-
-    >>> vigenere_decipher('hfnlp', 'abc')
-    'hello'
-    """
-    shifts = [ord(l) - ord('a') for l in sanitise(keyword)]
-    pairs = zip(message, cycle(shifts))
-    return ''.join([caesar_decipher_letter(l, k) for l, k in pairs])
-
-beaufort_encipher = vigenere_decipher
-beaufort_decipher = vigenere_encipher
-
-
 if __name__ == "__main__":
     import doctest
     doctest.testmod()
diff --git a/cipherbreak.py b/cipherbreak.py
index 9ce8000..f4c9c03 100644
--- a/cipherbreak.py
+++ b/cipherbreak.py
@@ -187,81 +187,6 @@ def keyword_break_worker(message, keyword, wrap_alphabet, fitness):
     return (keyword, wrap_alphabet), fit
 
 
-def vigenere_keyword_break_mp(message, wordlist=keywords, fitness=Pletters,
-                              chunksize=500):
-    """Breaks a vigenere cipher using a dictionary and frequency analysis.
-
-    >>> vigenere_keyword_break_mp(vigenere_encipher(sanitise('this is a test ' \
-             'message for the vigenere decipherment'), 'cat'), \
-             wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS
-    ('cat', -52.947271216...)
-    """
-    with Pool() as pool:
-        helper_args = [(message, word, fitness)
-                       for word in wordlist]
-        # Gotcha: the helper function here needs to be defined at the top level
-        #   (limitation of Pool.starmap)
-        breaks = pool.starmap(vigenere_keyword_break_worker, helper_args,
-                              chunksize)
-        return max(breaks, key=lambda k: k[1])
-vigenere_keyword_break = vigenere_keyword_break_mp
-
-def vigenere_keyword_break_worker(message, keyword, fitness):
-    plaintext = vigenere_decipher(message, keyword)
-    fit = fitness(plaintext)
-    logger.debug('Vigenere keyword break attempt using key {0} gives fit of '
-                 '{1} and decrypt starting: {2}'.format(keyword,
-                     fit, sanitise(plaintext)[:50]))
-    return keyword, fit
-
-
-def vigenere_frequency_break(message, max_key_length=20, fitness=Pletters):
-    """Breaks a Vigenere cipher with frequency analysis
-
-    >>> vigenere_frequency_break(vigenere_encipher(sanitise("It is time to " \
-            "run. She is ready and so am I. I stole Daniel's pocketbook this " \
-            "afternoon when he left his jacket hanging on the easel in the " \
-            "attic. I jump every time I hear a footstep on the stairs, " \
-            "certain that the theft has been discovered and that I will " \
-            "be caught. The SS officer visits less often now that he is " \
-            "sure"), 'florence')) # doctest: +ELLIPSIS
-    ('florence', -307.5473096791...)
-    """
-    def worker(message, key_length, fitness):
-        splits = every_nth(sanitised_message, key_length)
-        key = ''.join([chr(caesar_break(s)[0] + ord('a')) for s in splits])
-        plaintext = vigenere_decipher(message, key)
-        fit = fitness(plaintext)
-        return key, fit
-    sanitised_message = sanitise(message)
-    results = starmap(worker, [(sanitised_message, i, fitness)
-                               for i in range(1, max_key_length+1)])
-    return max(results, key=lambda k: k[1])
-
-
-def beaufort_frequency_break(message, max_key_length=20, fitness=Pletters):
-    """Breaks a Beaufort cipher with frequency analysis
-
-    >>> beaufort_frequency_break(beaufort_encipher(sanitise("It is time to " \
-            "run. She is ready and so am I. I stole Daniel's pocketbook this " \
-            "afternoon when he left his jacket hanging on the easel in the " \
-            "attic. I jump every time I hear a footstep on the stairs, " \
-            "certain that the theft has been discovered and that I will " \
-            "be caught. The SS officer visits less often now " \
-            "that he is sure"), 'florence')) # doctest: +ELLIPSIS
-    ('florence', -307.5473096791...)
-    """
-    def worker(message, key_length, fitness):
-        splits = every_nth(sanitised_message, key_length)
-        key = ''.join([chr(-caesar_break(s)[0] % 26 + ord('a'))
-                       for s in splits])
-        plaintext = beaufort_decipher(message, key)
-        fit = fitness(plaintext)
-        return key, fit
-    sanitised_message = sanitise(message)
-    results = starmap(worker, [(sanitised_message, i, fitness)
-                               for i in range(1, max_key_length+1)])
-    return max(results, key=lambda k: k[1])
 
 def plot_frequency_histogram(freqs, sort_key=None):
     x = range(len(freqs.keys()))