--- /dev/null
+from utilities import *
+from language_models import *
+from logger import logger
+
+
+modular_division_table = [[0]*26 for _ in range(26)]
+for a in range(26):
+ for b in range(26):
+ c = (a * b) % 26
+ modular_division_table[b][c] = a
+
+
+
+
+def affine_encipher_letter(accented_letter, multiplier=1, adder=0, one_based=True):
+ """Encipher a letter, given a multiplier and adder
+
+ >>> cat(affine_encipher_letter(l, 3, 5, True) \
+ for l in string.ascii_letters)
+ 'hknqtwzcfiloruxadgjmpsvybeHKNQTWZCFILORUXADGJMPSVYBE'
+ >>> cat(affine_encipher_letter(l, 3, 5, False) \
+ for l in string.ascii_letters)
+ 'filoruxadgjmpsvybehknqtwzcFILORUXADGJMPSVYBEHKNQTWZC'
+ """
+ # letter = unaccent(accented_letter)
+ # 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
+ # cipher_number = (letter_number * multiplier + adder) % 26
+ # if one_based: cipher_number -= 1
+ # return chr(cipher_number % 26 + alphabet_start)
+ # else:
+ # return letter
+ letter = unaccent(accented_letter)
+ if letter in string.ascii_letters:
+ letter_number = pos(letter)
+ if one_based: letter_number += 1
+ cipher_number = (letter_number * multiplier + adder) % 26
+ if one_based: cipher_number -= 1
+ if letter in string.ascii_uppercase:
+ return unpos(cipher_number).upper()
+ else:
+ return unpos(cipher_number)
+ else:
+ return letter
+
+def affine_decipher_letter(letter, multiplier=1, adder=0, one_based=True):
+ """Encipher a letter, given a multiplier and adder
+
+ >>> cat(affine_decipher_letter(l, 3, 5, True) \
+ for l in 'hknqtwzcfiloruxadgjmpsvybeHKNQTWZCFILORUXADGJMPSVYBE')
+ 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
+ >>> cat(affine_decipher_letter(l, 3, 5, False) \
+ for l in 'filoruxadgjmpsvybehknqtwzcFILORUXADGJMPSVYBEHKNQTWZC')
+ 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
+ """
+ # 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 = (
+ # modular_division_table[multiplier]
+ # [(cipher_number - adder) % 26])
+ # if one_based: plaintext_number -= 1
+ # return chr(plaintext_number % 26 + alphabet_start)
+ # else:
+ # return letter
+ if letter in string.ascii_letters:
+ cipher_number = pos(letter)
+ if one_based: cipher_number += 1
+ plaintext_number = (
+ modular_division_table[multiplier]
+ [(cipher_number - adder) % 26])
+ if one_based: plaintext_number -= 1
+ if letter in string.ascii_uppercase:
+ return unpos(plaintext_number).upper()
+ else:
+ return unpos(plaintext_number)
+ else:
+ return letter
+
+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 cat(enciphered)
+
+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 cat(enciphered)
+
+
+
+def affine_break(message, fitness=Pletters):
+ """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.') # doctest: +ELLIPSIS
+ ((15, 22, True), -340.601181913...)
+ """
+ sanitised_message = sanitise(message)
+ best_multiplier = 0
+ best_adder = 0
+ best_one_based = True
+ best_fit = float("-inf")
+ for one_based in [True, False]:
+ for multiplier in [x for x in range(1, 26, 2) if x != 13]:
+ for adder in range(26):
+ plaintext = affine_decipher(sanitised_message,
+ multiplier, adder, one_based)
+ fit = fitness(plaintext)
+ logger.debug('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_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
projects / cipher-tools.git / blobdiff