def _decode_16(self, key: str, cyphertext: str):
"""decodes a 16 byte string"""
key_array = Converter.make_array(key)
cyphertext_array = Converter.make_array(cyphertext)
# generate round keys
round_keys = self._generate_round_keys(
Converter.byte_to_hex(key_array))
# Add key0 to plaintext to start and first round
state_array = round_keys[10] ^ cyphertext_array
state_array = self._AES_decode_first_round(state_array)
# main 9 round loop
for i in range(1, 10):
round = 10 - i
state_array = self._AES_decode_round(state_array,
round_keys[round])
# final round
state_array = Converter.hex_to_byte(state_array)
final_array = state_array ^ key_array
return Converter.make_string(final_array)
def _AES_encode_last_round(self, state_array, round_key):
"""performs the last round of encoding"""
hex_array = Converter.byte_to_hex(state_array)
step1 = self.sbox.matrix_sbox_substitution(hex_array)
step2 = self._shift_rows(step1)
step2 = Converter.hex_to_byte(step2)
step3 = step2 ^ round_key
return step3
def _AES_decode_round(self, state_array, round_key):
"""reverses the steps of a signle encoding round"""
step1 = Converter.hex_to_byte(state_array)
step1 = step1 ^ round_key
step2 = self._inverse_mix_columns(step1)
step2 = Converter.byte_to_hex(step2)
step3 = self._inverse_shift_rows(step2)
step4 = self.inverse_sbox.matrix_sbox_substitution(step3)
return step4
def test_hex_to_byte(self):
self.assertTrue(
np.array_equal(Converter.hex_to_byte(self.test_hex),
self.test_bytes))