From: Neil Smith Date: Mon, 14 Jul 2014 19:56:24 +0000 (+0100) Subject: Breaking caesar ciphers X-Git-Url: https://git.njae.me.uk/?a=commitdiff_plain;h=25fe3d49e738be3e1f03d15445cad78bf1c94bde;p=cipher-training.git Breaking caesar ciphers --- diff --git a/cipher.py b/cipher.py index 5398714..e71902d 100644 --- a/cipher.py +++ b/cipher.py @@ -9,73 +9,6 @@ from itertools import zip_longest, cycle, chain from language_models import unaccent, sanitise -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 every_nth(text, n, fillvalue=''): - """Returns n strings, each of which consists of every nth character, - starting with the 0th, 1st, 2nd, ... (n-1)th character - - >>> every_nth(string.ascii_lowercase, 5) - ['afkpuz', 'bglqv', 'chmrw', 'dinsx', 'ejoty'] - >>> every_nth(string.ascii_lowercase, 1) - ['abcdefghijklmnopqrstuvwxyz'] - >>> every_nth(string.ascii_lowercase, 26) # doctest: +NORMALIZE_WHITESPACE - ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', - 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] - >>> every_nth(string.ascii_lowercase, 5, fillvalue='!') - ['afkpuz', 'bglqv!', 'chmrw!', 'dinsx!', 'ejoty!'] - """ - split_text = chunks(text, n, fillvalue) - return [''.join(l) for l in zip_longest(*split_text, fillvalue=fillvalue)] - -def combine_every_nth(split_text): - """Reforms a text split into every_nth strings - - >>> combine_every_nth(every_nth(string.ascii_lowercase, 5)) - 'abcdefghijklmnopqrstuvwxyz' - >>> combine_every_nth(every_nth(string.ascii_lowercase, 1)) - 'abcdefghijklmnopqrstuvwxyz' - >>> combine_every_nth(every_nth(string.ascii_lowercase, 26)) - 'abcdefghijklmnopqrstuvwxyz' - """ - return ''.join([''.join(l) - for l in zip_longest(*split_text, fillvalue='')]) - -def chunks(text, n, fillvalue=None): - """Split a text into chunks of n characters - - >>> chunks('abcdefghi', 3) - ['abc', 'def', 'ghi'] - >>> chunks('abcdefghi', 4) - ['abcd', 'efgh', 'i'] - >>> chunks('abcdefghi', 4, fillvalue='!') - ['abcd', 'efgh', 'i!!!'] - """ - if fillvalue: - padding = fillvalue[0] * (n - len(text) % n) - else: - padding = '' - return [(text+padding)[i:i+n] for i in range(0, len(text), n)] - -def deduplicate(text): - """If a string contains duplicate letters, remove all but the first. Retain - the order of the letters. - - >>> deduplicate('cat') - ['c', 'a', 't'] - >>> deduplicate('happy') - ['h', 'a', 'p', 'y'] - >>> deduplicate('cattca') - ['c', 'a', 't'] - """ - return list(collections.OrderedDict.fromkeys(text)) - - def caesar_encipher_letter(accented_letter, shift): """Encipher a letter, given a shift amount @@ -152,78 +85,6 @@ def caesar_decipher(message, shift): """ return caesar_encipher(message, -shift) -def affine_encipher_letter(accented_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' - """ - 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 - -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 = ( - modular_division_table[multiplier] - [(cipher_number - adder) % 26] - ) - if one_based: plaintext_number -= 1 - return chr(plaintext_number % 26 + 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) - if __name__ == "__main__": import doctest