logger = logging.getLogger(__name__)
logger.addHandler(logging.FileHandler('cipher.log'))
-# logging.basicConfig(filename='cipher.log',level=logging.WARNING)
+logger.setLevel(logging.WARNING)
logger.setLevel(logging.INFO)
english_counts = collections.defaultdict(int)
c = (a * b) % 26
modular_division_table[b][c] = a
+modular_division_table_one_based = [[0]*27 for x in range(27)]
+for a in range(27):
+ for b in range(27):
+ c = ((a * b)-1) % 26 + 1
+ modular_division_table_one_based[b][c] = a
+
+
def sanitise(text):
"""Remove all non-alphabetic characters and convert the text to lowercase
"""
return caesar_encipher(message, -shift)
-def affine_encipher_letter(letter, multiplier, adder, multiply_then_add=True):
+def affine_encipher_letter(letter, multiplier=1, adder=0, one_based=True):
+ """Encipher a letter, given a multiplier and adder
+
+ >>> ''.join([affine_encipher_letter(l, 3, 5, True) for l in string.ascii_uppercase])
+ 'HKNQTWZCFILORUXADGJMPSVYBE'
+ >>> ''.join([affine_encipher_letter(l, 3, 5, False) for l in string.ascii_uppercase])
+ 'FILORUXADGJMPSVYBEHKNQTWZC'
+ """
if letter in string.ascii_letters:
if letter in string.ascii_uppercase:
alphabet_start = ord('A')
else:
alphabet_start = ord('a')
letter_number = ord(letter) - alphabet_start
+ if one_based: letter_number += 1
+ raw_cipher_number = (letter_number * multiplier + adder)
cipher_number = 0
- if multiply_then_add:
- cipher_number = (letter_number * multiplier + adder) % 26
+ if one_based:
+ cipher_number = (raw_cipher_number - 1) % 26
else:
- cipher_number = ((letter_number + adder) * multiplier) % 26
+ cipher_number = raw_cipher_number % 26
return chr(cipher_number + alphabet_start)
else:
return letter
-def affine_decipher_letter(letter, multiplier, adder, multiply_then_add=True):
+def affine_decipher_letter(letter, multiplier=1, adder=0, one_based=True):
+ """Encipher a letter, given a multiplier and adder
+
+ >>> ''.join([affine_decipher_letter(l, 3, 5, True) for l in 'HKNQTWZCFILORUXADGJMPSVYBE'])
+ 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+ >>> ''.join([affine_decipher_letter(l, 3, 5, False) for l in 'FILORUXADGJMPSVYBEHKNQTWZC'])
+ 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+ """
if letter in string.ascii_letters:
if letter in string.ascii_uppercase:
alphabet_start = ord('A')
else:
alphabet_start = ord('a')
cipher_number = ord(letter) - alphabet_start
+ if one_based: cipher_number += 1
plaintext_number = 0
- if multiply_then_add:
- plaintext_number = modular_division_table[multiplier][(cipher_number - adder + 26) % 26]
+ if one_based:
+ plaintext_number = (modular_division_table_one_based[multiplier][(cipher_number - adder + 26) % 26] - 1) % 26
else:
- plaintext_number = (modular_division_table[multiplier][cipher_number] - adder) % 26
+ #plaintext_number = (modular_division_table[multiplier][cipher_number] - adder) % 26
+ plaintext_number = modular_division_table[multiplier][(cipher_number - adder + 26) % 26]
return chr(plaintext_number + alphabet_start)
else:
return letter
-def affine_encipher(message, multiplier, adder, multiply_then_add=True):
- enciphered = [affine_encipher_letter(l, multiplier, adder, multiply_then_add) for l in message]
+def affine_encipher(message, multiplier=1, adder=0, one_based=True):
+ """Encipher a message
+
+ >>> affine_encipher('hours passed during which jerico tried every trick he could think of', 15, 22, True)
+ 'lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg jfaoe ls omytd jlaxe mh'
+ """
+
+ enciphered = [affine_encipher_letter(l, multiplier, adder, one_based) for l in message]
return ''.join(enciphered)
-def affine_decipher(message, multiplier, adder, multiply_then_add=True):
- enciphered = [affine_decipher_letter(l, multiplier, adder, multiply_then_add) for l in message]
+def affine_decipher(message, multiplier=1, adder=0, one_based=True):
+ """Decipher a message
+
+ >>> affine_decipher('lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg jfaoe ls omytd jlaxe mh', 15, 22, True)
+ 'hours passed during which jerico tried every trick he could think of'
+ """
+ enciphered = [affine_decipher_letter(l, multiplier, adder, one_based) for l in message]
return ''.join(enciphered)
def affine_break(message, metric=norms.euclidean_distance, target_frequencies=normalised_english_counts, message_frequency_scaling=norms.normalise):
"""Breaks an affine cipher using frequency analysis
+
+ >>> affine_break('lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg jfaoe ls omytd jlaxe mh jm bfmibj umis hfsul axubafkjamx. ls kffkxwsd jls ofgbjmwfkiu olfmxmtmwaokttg jlsx ls kffkxwsd jlsi zg tsxwjl. jlsx ls umfjsd jlsi zg hfsqysxog. ls dmmdtsd mx jls bats mh bkbsf. ls bfmctsd kfmyxd jls lyj, mztanamyu xmc jm clm cku tmmeaxw kj lai kxd clm ckuxj.')
+ ((15, 22, True), 0.2357036181865554)
"""
sanitised_message = sanitise(message)
best_multiplier = 0
best_adder = 0
- best_multiply_then_add = True
+ best_one_based = True
best_fit = float("inf")
- for multiply_then_add in [True, False]:
+ for one_based in [True, False]:
for multiplier in range(1, 26, 2):
for adder in range(26):
- plaintext = affine_decipher(sanitised_message, multiplier, adder, multiply_then_add)
+ plaintext = affine_decipher(sanitised_message, multiplier, adder, one_based)
frequencies = message_frequency_scaling(letter_frequencies(plaintext))
fit = metric(target_frequencies, frequencies)
- logger.info('Affine break attempt using key {0}x+{1} ({2}) gives fit of {3} and decrypt starting: {4}'.format(multiplier, adder, multiply_then_add, fit, plaintext[:50]))
+ logger.info('Affine break attempt using key {0}x+{1} ({2}) gives fit of {3} and decrypt starting: {4}'.format(multiplier, adder, one_based, fit, plaintext[:50]))
if fit < best_fit:
best_fit = fit
best_multiplier = multiplier
best_adder = adder
- best_multiply_then_add = multiply_then_add
- logger.info('Affine break best fit with key {0}x+{1} ({2}) gives fit of {3} and decrypt starting: {4}'.format(best_multiplier, best_adder, best_multiply_then_add, best_fit, affine_decipher(sanitised_message, best_multiplier, best_adder, best_multiply_then_add)[:50]))
- return (best_multiplier, best_adder, best_multiply_then_add), best_fit
+ best_one_based = one_based
+ logger.info('Affine break best fit with key {0}x+{1} ({2}) gives fit of {3} and decrypt starting: {4}'.format(best_multiplier, best_adder, best_one_based, best_fit, affine_decipher(sanitised_message, best_multiplier, best_adder, best_one_based)[:50]))
+ return (best_multiplier, best_adder, best_one_based), best_fit
if __name__ == "__main__":
projects / cipher-tools.git / blobdiff