def DecryptAES(cipher, key):
"""
not using the cooler equivalent inverse cause i don't want to make a different key schedule too
"""
if len(key) != 16:
raise ValueError(
"Key must be 16 bytes (for AES-128, I didn't implement others)")
# get round keys
round_keys = MakeRoundKeys(exp_key=KeyExpansion(key, Nk=4), rounds=11)
# convert cipher to blocks
cipher_blocks = [cipher[i:i + 16] for i in range(0, len(cipher), 16)]
msg_blocks = [None] * len(cipher_blocks)
for m in range(len(cipher_blocks)):
state = cipher_blocks[m]
h_state = ' '.join(
[state.hex()[i:i + 2] for i in range(0, len(state.hex()), 2)])
# undo rounds 11-2
for r in range(10, 0, -1):
state = AddRoundKey(state, round_keys[r])
h_state = ' '.join(
[state.hex()[i:i + 2] for i in range(0, len(state.hex()), 2)])
if r != 10:
state = InvMixColumns(state)
h_state = ' '.join([
state.hex()[i:i + 2]
for i in range(0, len(state.hex()), 2)
])
state = InvShiftRows(state)
h_state = ' '.join(
[state.hex()[i:i + 2] for i in range(0, len(state.hex()), 2)])
state = InvSubBytes(state)
h_state = ' '.join(
[state.hex()[i:i + 2] for i in range(0, len(state.hex()), 2)])
# undo round 1
state = AddRoundKey(state, round_keys[0])
h_state = ' '.join(
[state.hex()[i:i + 2] for i in range(0, len(state.hex()), 2)])
msg_blocks[m] = state
# unpad message
return unpad(b''.join(msg_blocks))
def decrypt(self, ciphertext):
# break plaintext into chunks
cipher_blocks = [
ciphertext[i:i + 16] for i in range(0, len(ciphertext), 16)
]
# initialize encrypted blocks
msg_blocks = [None] * len(cipher_blocks)
for m in range(0, len(cipher_blocks)):
# use block cipher FIRST this time
msg_blocks[m] = self._aes_cipher.decrypt(cipher_blocks[m])
# then xor prev CIPHERTEXT block
if m == 0:
msg_blocks[m] = xor(msg_blocks[m], self._iv)
else:
msg_blocks[m] = xor(msg_blocks[m], cipher_blocks[m - 1])
msg = unpad(b''.join(msg_blocks), 16).decode('ascii')
return b''.join(msg_blocks).decode('ascii')
def decrypt(self, ciphertext):
return unpad(self._aes_cipher.decrypt(ciphertext))
from s02_c09 import unpad
if __name__ == '__main__':
assert unpad("ICE ICE BABY\x04\x04\x04\x04") == "ICE ICE BABY"
# should figure out how to unit test raised exceptions eventually
unpad("ICE ICE BABY\x01\x02\x03\x04")