def single_byte_xor_break(hexstring):
"""Try to decrypt a hex strings that has been encrypted with a one Byte key
:param hexstring: The hex encoded, one Byte XOR encrypted data to brute force
:return: A tuple containing the key at position 0 and the decrypted string at position 1.
"""
hexstring_bytes = hexstring_to_bytelist(hexstring)
# Try every byte counting the number of letters for each decrypt
best_guess_num_letters = None
best_guess = None
best_guess_key = None
for i in xrange(0, 255):
decrypt = [chr(byte ^ i) for byte in hexstring_bytes]
num_letters = sum(1 for c in decrypt if c.isalpha() or c.isspace())
# We'll assume the guess that decrypts to the maximum number
# of letters is the correct guess
if num_letters > best_guess_num_letters:
best_guess_num_letters = num_letters
best_guess = ''.join(decrypt)
best_guess_key = i
return best_guess_key, best_guess
def test_hexstring_to_bytelist():
assert cc_util.hexstring_to_bytelist('01020304050a0b0c0d10') == [1, 2, 3, 4, 5, 10, 11, 12, 13, 16]
