def test_decrypt(self):
cipher = Transposition()
open_text = normalize_text("Python is a general-purpose, interpreted high-level programming language")
key = "password"
cipher_text = cipher.encrypt(open_text, key)
decrypted_text = cipher.decrypt(cipher_text, key)
expected = open_text + "xx"
self.assertEqual(decrypted_text, expected)
class LongWordAttack(object):
"""Cryptanalysis method for transposition cipher"""
def __init__(self):
super(LongWordAttack, self).__init__()
self.max_keylen = 15
self.transposition = Transposition()
def crack(self, cipher_text, langstats):
key_text_pair = lambda key: (
key, self.transposition.decrypt(cipher_text, key))
key_text = (key_text_pair(key)
for key in self._get_possible_keys(cipher_text, langstats))
return langstats.most_meaningful(key_text)
def _get_possible_keys(self, cipher_text, langstats):
reshuffle_text = self.transposition._partition_text_decrypt
for keylen in self._key_lengths(cipher_text):
all_words = langstats.get_words(keylen)
for cipher_word in reshuffle_text(cipher_text,
len(cipher_text) / keylen):
cipher_counter = Counter(cipher_word)
for real_word in all_words:
if Counter(real_word) == cipher_counter:
for key in self._get_valid_keys(
cipher_word, real_word):
yield key
def _get_valid_keys(self, cipher_word, real_word):
for perm in self._get_perms(cipher_word, 0, [],
self.get_positions(real_word)):
yield "".join(chr(x + ord('a')) for x in perm)
def _get_perms(self, word, currPos, visited, positions):
if currPos == len(word):
yield visited
else:
c = word[currPos]
for free in positions[c] - set(visited):
for vis in self._get_perms(word, currPos + 1, visited + [free],
positions):
yield vis
def get_positions(self, word):
pos = {}
for i, char in enumerate(word):
if char in pos:
pos[char].add(i)
else:
pos[char] = {i}
return pos
def _key_lengths(self, cipher_text):
ltext = len(cipher_text)
return (i for i in range(2, self.max_keylen + 1) if ltext % i == 0)
class LongWordAttack(object):
"""Cryptanalysis method for transposition cipher"""
def __init__(self):
super(LongWordAttack, self).__init__()
self.max_keylen = 15
self.transposition = Transposition()
def crack(self, cipher_text, langstats):
key_text_pair = lambda key: (key, self.transposition.decrypt(cipher_text, key))
key_text = (key_text_pair(key) for key in self._get_possible_keys(cipher_text, langstats))
return langstats.most_meaningful(key_text)
def _get_possible_keys(self, cipher_text, langstats):
reshuffle_text = self.transposition._partition_text_decrypt
for keylen in self._key_lengths(cipher_text):
all_words = langstats.get_words(keylen)
for cipher_word in reshuffle_text(cipher_text, len(cipher_text) / keylen):
cipher_counter = Counter(cipher_word)
for real_word in all_words:
if Counter(real_word) == cipher_counter:
for key in self._get_valid_keys(cipher_word, real_word):
yield key
def _get_valid_keys(self, cipher_word, real_word):
for perm in self._get_perms(cipher_word, 0, [], self.get_positions(real_word)):
yield "".join(chr(x + ord('a')) for x in perm)
def _get_perms(self, word, currPos, visited, positions):
if currPos == len(word):
yield visited
else:
c = word[currPos]
for free in positions[c] - set(visited):
for vis in self._get_perms(word, currPos + 1, visited + [free], positions):
yield vis
def get_positions(self, word):
pos = {}
for i, char in enumerate(word):
if char in pos:
pos[char].add(i)
else:
pos[char] = {i}
return pos
def _key_lengths(self, cipher_text):
ltext = len(cipher_text)
return (i for i in range(2, self.max_keylen + 1) if ltext % i == 0)
