To keep it short: I am sending an encrypted message (AES with CBC) to another service, and it returns me an encrypted response, but I can't decrypt it because they are not using padding? (to be honest, I don't know much about encryption and its mechanisms).
This is my implementation (based on the documentation) of a class used to encrypt and decrypt messages.
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad
class AESCipher:
def __init__(self, key, iv):
self.key = bytes.fromhex(key)
self.iv = bytes.fromhex(iv)
def encrypt(self, msg):
msg = pad(msg.encode(), AES.block_size)
cipher = AES.new(self.key, AES.MODE_CBC, self.iv)
return cipher.encrypt(msg)
def decrypt(self, msg):
cipher = AES.new(self.key, AES.MODE_CFB, self.iv)
return unpad(cipher.decrypt(msg), AES.block_size)
I can easily encrypt (and even decrypt my own message) using this implementation, but the actual response from the host always fails to decrypt. First I thought it was a problem with the host, but when I use an AES online tool, it kinda works (I used this one)
To reproduce the issue, I send a malformed message and receive an encrypted error:
msg = b"X\xb4\xc6\xc9j\x92\x8f\xe5\x84\xe5\\N7\x8bv\xb8\x02\x0e\xed*\xe7\x92\xdd/\xf1\xff\xdfj 5\x00\x91\xb5;\xb6Q\x08\xc8\xf1PFF\x1aw\x93\xa7\xbe\xa7\xafD\xe7:=\x8b\x1d\x86i\xa8\x95\x107\xf2\xbcF1\x80D\x8c\x98\x1f\xfc\x80\xc3\xd6\x81'\xf3\xd98\x93\x8bv\xf7P\xc9\xb1L,\x8aJ\x05\xd8\xd0P\x10\rQ\xba\xf5&4\x0e\xf0\x97\xf5\xa5B\xb7\xbda_?\xcbk~\xe6\xfe\xf6\x8f\x92\x1b;#\xd2\x87\xc6^\n"
The key and iv are:
key = AEC273769C9C4E9830D5FA3929BE1F5115E4BF085BCBA6ACCBAEF63E654D8AE3
iv = ACE499278E5FDC6849DDF23A8966D7CF
I get this error:
File "/home/richter/Code/Test_encryption/encryptation.py", line 22, in decrypt
return unpad(uncrypt, AES.block_size)
File "/home/richter/Code/Test_encryption/.venv/lib64/python3.10/site-packages/Crypto/Util/Padding.py", line 92, in unpad
raise ValueError("Padding is incorrect.")
ValueError: Padding is incorrect.
I also tried a different library, one written entirely in python (and boy, it's slow) but got the same issue with the size of the package.
