def test_1_fixed_length_XOR_with_unequal_length_buffers_should_truncate(
self):
a = '5468697320697320612074657374206d6573736167652e'
b = '4e61727920626565662e20556e6c65737320646561642e'
excess = 'deadbeef' * 5
expected = bytes.fromhex(
'1a091b0a000b1645070e54301d18451e16531704060100')
result0 = fixedXOR(a + excess, b)
result1 = fixedXOR(a, b + excess)
self.assertEqual(result0, expected)
self.assertEqual(result1, expected)
def _crackRepeatingXOR(byteObject, frequentLetters, keySizeRange, blockNumber):
if not isBytes(byteObject):
raise ValueError("Input must be a bytes object")
keySizes = getLikelyKeySizes(byteObject,
keySizeRange,
blockNumber,
howMany=3)
bestGuess = Candidate(0, b'', b'', b'')
for keySize in keySizes:
blocks = divideIntoBlocks(byteObject, keySize)
possibleKey = bytearray()
for block in blocks:
candidate = _crackSingleXOR(block, frequentLetters)
# This key length can never be the correct key length
if candidate.key == b'':
break
possibleKey.append(candidate.key[0])
if len(possibleKey) != keySize:
continue
possibleKey = bytes(possibleKey)
secret = fixedXOR(byteObject,
repeatPerCharacter(possibleKey, len(byteObject)))
score = calculateScore(secret, frequentLetters)
if score > bestGuess.score and encodedByUTF8(secret):
bestGuess = Candidate(score, possibleKey, byteObject, secret)
return bestGuess
def test_0_fixed_length_XOR_with_equal_length_buffers(self):
a = '5468697320697320612074657374206d6573736167652e'
b = '4e61727920626565662e20556e6c65737320646561642e'
expected = bytes.fromhex(
'1a091b0a000b1645070e54301d18451e16531704060100')
result = fixedXOR(a, b)
self.assertEqual(result, expected)
def fixed_XOR():
# Set up
args = getArgs()
challengeData = getData()[getFilename(__file__)]
if args.input:
challengeData['values'] = args.input
# Complete challenge
values = challengeData['values']
output = fixedXOR(values[0], values[1])
challengeData['output'] = bytes2hex(output)
return challengeData
def _crackSingleXOR(byteObject, frequentLetters):
if not isBytes(byteObject):
raise ValueError("Input must be a bytes object")
bestCandidate = Candidate(0, b'', b'', b'')
# We skip 0, since XORing against a bunch of 0s isn't going to do anything
byteLength = len(byteObject)
for i in range(1, 256):
possibleKey = repeatPerCharacter(bytes([i]), byteLength)
secret = fixedXOR(byteObject, possibleKey)
score = calculateScore(secret, frequentLetters)
if score > bestCandidate.score and encodedByUTF8(secret):
bestCandidate = Candidate(score, possibleKey, byteObject, secret)
return bestCandidate