+ """Decipher a letter, given a shift amount
+
+ >>> caesar_decipher_letter('b', 1)
+ 'a'
+ >>> caesar_decipher_letter('b', 2)
+ 'z'
+ """
+ return caesar_encipher_letter(letter, -shift)
+
+def caesar_encipher(message, shift):
+ """Encipher a message with the Caesar cipher of given shift
+
+ >>> caesar_encipher('abc', 1)
+ 'bcd'
+ >>> caesar_encipher('abc', 2)
+ 'cde'
+ >>> caesar_encipher('abcxyz', 2)
+ 'cdezab'
+ >>> caesar_encipher('ab cx yz', 2)
+ 'cd ez ab'
+ """
+ enciphered = [caesar_encipher_letter(l, shift) for l in message]
+ return ''.join(enciphered)
+
+def caesar_decipher(message, shift):
+ """Encipher a message with the Caesar cipher of given shift
+
+ >>> caesar_decipher('bcd', 1)
+ 'abc'
+ >>> caesar_decipher('cde', 2)
+ 'abc'
+ >>> caesar_decipher('cd ez ab', 2)
+ 'ab cx yz'
+ """
+ return caesar_encipher(message, -shift)
+
+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 one_based:
+ cipher_number = (raw_cipher_number - 1) % 26
+ else:
+ cipher_number = raw_cipher_number % 26
+ return chr(cipher_number + alphabet_start)
+ else:
+ return letter
+
+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 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) % 26]
+ return chr(plaintext_number + alphabet_start)
+ 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 ''.join(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 ''.join(enciphered)
+
+
+def keyword_encipher(message, keyword, wrap_alphabet=False):
+ cipher_alphabet = ''
+ if wrap_alphabet:
+ last_keyword_letter = deduplicate(sanitise(keyword))[-1]
+ last_keyword_position = string.ascii_lowercase.find(last_keyword_letter) + 1
+ cipher_alphabet = ''.join(deduplicate(sanitise(keyword) + string.ascii_lowercase[last_keyword_position:] + string.ascii_lowercase[:last_keyword_position]))
+ else:
+ cipher_alphabet = ''.join(deduplicate(sanitise(keyword) + string.ascii_lowercase))
+ cipher_translation = ''.maketrans(string.ascii_lowercase, cipher_alphabet)
+ return message.lower().translate(cipher_translation)
+
+def keyword_decipher(message, keyword, wrap_alphabet=False):
+ cipher_alphabet = ''
+ if wrap_alphabet:
+ last_keyword_letter = deduplicate(sanitise(keyword))[-1]
+ last_keyword_position = string.ascii_lowercase.find(last_keyword_letter) + 1
+ cipher_alphabet = ''.join(deduplicate(sanitise(keyword) + string.ascii_lowercase[last_keyword_position:] + string.ascii_lowercase[:last_keyword_position]))
+ else:
+ cipher_alphabet = ''.join(deduplicate(sanitise(keyword) + string.ascii_lowercase))
+ #cipher_alphabet = ''.join(deduplicate(sanitise(keyword) + string.ascii_lowercase))
+ cipher_translation = ''.maketrans(cipher_alphabet, string.ascii_lowercase)
+ return message.lower().translate(cipher_translation)
+
+
+def caesar_break(message, metric=norms.euclidean_distance, target_frequencies=normalised_english_counts, message_frequency_scaling=norms.normalise):
+ """Breaks a Caesar cipher using frequency analysis
+
+ >>> caesar_break('ibxcsyorsaqcheyklxivoexlevmrimwxsfiqevvmihrsasrxliwyrhecjsppsamrkwleppfmergefifvmhixscsymjcsyqeoixlm')
+ (4, 0.31863952890183...)
+ >>> caesar_break('wxwmaxdgheetgwuxztgptedbgznitgwwhpguxyhkxbmhvvtlbhgteeraxlmhiixweblmxgxwmhmaxybkbgztgwztsxwbgmxgmert')
+ (19, 0.42152901235832...)
+ >>> caesar_break('yltbbqnqnzvguvaxurorgenafsbezqvagbnornfgsbevpnaabjurersvaquvzyvxrnznazlybequrvfohgriraabjtbaruraprur')
+ (13, 0.316029208075451...)
+ """
+ sanitised_message = sanitise(message)
+ best_shift = 0
+ best_fit = float("inf")
+ for shift in range(26):
+ plaintext = caesar_decipher(sanitised_message, shift)
+ frequencies = message_frequency_scaling(letter_frequencies(plaintext))
+ fit = metric(target_frequencies, frequencies)
+ logger.info('Caesar break attempt using key {0} gives fit of {1} and decrypt starting: {2}'.format(shift, fit, plaintext[:50]))
+ if fit < best_fit:
+ best_fit = fit
+ best_shift = shift
+ logger.info('Caesar break best fit: key {0} gives fit of {1} and decrypt starting: {2}'.format(best_shift, best_fit, caesar_decipher(sanitised_message, best_shift)[:50]))
+ return best_shift, best_fit
+
+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), 0.23570361818655...)
+ """
+ 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 range(1, 26, 2):
+ for adder in range(26):
+ 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, 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
+
+
+def keyword_break(message, metric=norms.euclidean_distance, target_frequencies=normalised_english_counts, message_frequency_scaling=norms.normalise):
+ best_keyword = ''
+ best_wrap_alphabet = True
+ best_fit = float("inf")
+ for wrap_alphabet in [True, False]:
+ for keyword in keywords:
+ plaintext = keyword_decipher(message, keyword, wrap_alphabet)
+ frequencies = message_frequency_scaling(letter_frequencies(plaintext))
+ fit = metric(target_frequencies, frequencies)
+ logger.info('Keyword break attempt using key {0} ({1}) gives fit of {2} and decrypt starting: {3}'.format(keyword, wrap_alphabet, fit, sanitise(plaintext)[:50]))
+ if fit < best_fit:
+ best_fit = fit
+ best_keyword = keyword
+ best_wrap_alphabet = wrap_alphabet
+ logger.info('Keyword break best fit with key {0} ({1}) gives fit of {2} and decrypt starting: {3}'.format(best_keyword, best_wrap_alphabet, best_fit, sanitise(keyword_decipher(message, best_keyword))[:50]))
+ return (best_keyword, best_wrap_alphabet), best_fit