code.kerkeslager.com Git - sandbox/blob - cryptopals-python/cryptopals.py

   1 import codecs
   2 import unittest
   3
   4 def base64_from_hex(_hex):
   5     return codecs.encode(bytes.fromhex(_hex), 'base64').decode('utf-8')
   6
   7 def xor_bytes(bytes0, bytes1):
   8     return bytes(b0 ^ b1 for b0, b1 in zip(bytes0, bytes1))
   9
  10 def xor_hex(hex0, hex1):
  11     assert len(hex0) == len(hex1)
  12     bytes0 = bytes.fromhex(hex0)
  13     bytes1 = bytes.fromhex(hex1)
  14     return codecs.encode(xor_bytes(bytes0, bytes1), 'hex').decode('utf-8')
  15
  16 def get_character_frequencies(source):
  17     frequencies = {}
  18
  19     for source_character in source:
  20         frequencies[source_character] = frequencies.get(source_character, 0) + 1
  21
  22     return frequencies
  23
  24 def compare_frequency_deviation(base_frequency, comparison_frequency):
  25     return sum(
  26         abs(frequency - comparison_frequency.get(character, 0))
  27         for character, frequency in base_frequency.items()
  28     ) / len(base_frequency)
  29
  30 class Set1Challenge1Tests(unittest.TestCase):
  31     def test_converts_hex_to_base64(self):
  32         expected = 'SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t\n'
  33         actual = base64_from_hex('49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d')
  34         self.assertEqual(expected, actual)
  35
  36 class Set1Challenge2Tests(unittest.TestCase):
  37     def test_xors_hex_strings(self):
  38         hex0 = '1c0111001f010100061a024b53535009181c'
  39         hex1 = '686974207468652062756c6c277320657965'
  40
  41         expected = '746865206b696420646f6e277420706c6179'
  42         actual = xor_hex(hex0, hex1)
  43
  44         self.assertEqual(expected, actual)
  45
  46 class Set1Challenge3Tests(unittest.TestCase):
  47     def test_gets_message(self):
  48         with open('sample.txt','r') as sample_file:
  49             sample_text = sample_file.read()
  50
  51         sample_frequencies = get_character_frequencies(sample_text)
  52
  53         xored_string = bytes.fromhex('1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736')
  54
  55         lowest_frequency_deviation_string = None
  56         lowest_frequency_deviation = None
  57
  58         for i in range(128):
  59             key_char = bytes([i]).decode('utf-8')
  60             key = bytes([i]) * len(xored_string)
  61             try_string = xor_bytes(xored_string, key).decode('utf-8')
  62             try_string_frequency_deviation = compare_frequency_deviation(
  63                 sample_frequencies,
  64                 get_character_frequencies(try_string),
  65             )
  66
  67             if lowest_frequency_deviation is None or try_string_frequency_deviation < lowest_frequency_deviation:
  68                 lowest_frequency_deviation_string = try_string
  69                 lowest_frequency_deviation = try_string_frequency_deviation
  70
  71
  72         expected = "Cooking MC's like a pound of bacon"
  73         actual = lowest_frequency_deviation_string
  74
  75         self.assertEqual(expected, actual)
  76
  77 if __name__ == '__main__':
  78     unittest.main()