(letter, count) = line.split("\t")
english_counts[letter] = int(count)
+modular_division = [[0]* 26 for i in range(26)]
+for i in range(26):
+ for j in range(26):
+ t = (i*j) % 26
+ # therefore, i = t / j
+ modular_division[t][j] = i
+
+
def sanitise(text):
sanitised = [c.lower() for c in text if c in string.ascii_letters]
return ''.join(sanitised)
else:
return letter
-
+def affine_decipher_letter(letter, multiplier, shift, one_based=True):
+ if letter in string.ascii_letters:
+ if letter in string.ascii_lowercase:
+ alphastart = ord('a')
+ else:
+ alphastart = ord('A')
+ letter_number = ord(letter) - alphastart
+ if one_based: letter_number +=1
+ after_unshift = letter_number - shift
+ deciphered_letter_number = modular_division[after_unshift % 26][multiplier]
+ if one_based: deciphered_letter_number -=1
+ deciphered_letter = chr(deciphered_letter_number % 26 + alphastart)
+ return deciphered_letter
+ else:
+ return letter
+
+def affine_cipher_message(message, multiplier, shift, one_based=True):
+ big_cipher = [affine_cipher_letter(l, multiplier, shift, one_based) for l in message]
+ return ''.join(big_cipher)
+
+def affine_decipher_message(message, multiplier, shift, one_based=True):
+ big_decipher = [affine_decipher_letter(l, multiplier, shift, one_based) for l in message]
+ return ''.join(big_decipher)
def caesar_break(message):
best_fit = fit
return best_key
+def affine_break(message):
+ best_key = (0, 0, 0)
+ best_fit = float("inf")
+ for multiplier in range(1, 26, 2):
+ for shift in range(26):
+ for one_based in [True, False]:
+ plaintxt = affine_decipher_message(message, multiplier, shift, one_based)
+ lettertxt = letter_frequencies(plaintxt)
+ total1 = scale_freq(lettertxt)
+ total2 = scale_freq(english_counts)
+ fit = value_diff(total2, total1)c
+ if fit < best_fit:
+ best_key = (multiplier, shift, one_based)
+ best_fit = fit
+ return best_key