Decrypting AES Encrypted Data with no IV

Question

The AES Encrypted data I'm trying to decrypt is :

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

The key is :

02f3ffa287f78ba68c60f24f79c6fb18ce32b4ebaadac11af5ace8c67a50ae9f

There is no IV provided, a friend advised me to assume the first "block" from the encrypted data is the IV.

I wrote this code to decrypt it in Python:

from Crypto.Cipher import AES
from Crypto.Util.Padding import unpad
import binascii

def decrypt_aes(data, key, iv):
    cipher = AES.new(binascii.unhexlify(key), AES.MODE_CBC, binascii.unhexlify(iv))
    decrypted_data = unpad(cipher.decrypt(binascii.unhexlify(data)), AES.block_size)
    return decrypted_data.decode('utf-8')

# Input data, key, and IV
encrypted_data = '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'
encryption_key = '02f3ffa287f78ba68c60f24f79c6fb18ce32b4ebaadac11af5ace8c67a50ae9f'
iv = '40b6b8e3d1f7b712'

# Decrypt the data
decrypted_data = decrypt_aes(encrypted_data, encryption_key, iv)

# Print the result
print("Decrypted Data:", decrypted_data)

Throws this error:

ValueError: Incorrect IV length (it must be 16 bytes long)

I'm making several assumptions here:

• The decrypted data is assumed to be in UTF-8 encoding
• binascii.unhexlify(data), I jusf learned about AES encryption laat night and I'm using this line as the "normal" thing to do. Does it apply to my case?
• I'm not sure if the data or key is Hex or Base64. The key is 64 characters so I assume it's Hex.

Here's the file whose contents I'm trying to decrypt for reference: https://drive.google.com/file/d/1o79Bi9l4F_Dohef6Di3q_IKmzvKIx_2p/view?usp=sharing I'm trying to mod a game for personal use (activate mouse control, remove menu/dialogue restriction).

Answer 1

The number of hexadecimal characters is double the size of the binary data they represent. For an IV of 16 bytes you'll need 32 characters. But in code I'd first decode the ciphertext including IV, and then take the IV. You don't want that part to be reliant of the type of text encoding used.

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As for your comments:

The decrypted data is assumed to be in UTF-8 encoding

That will mostly work (assuming that the message is indeed text), but don't forget that e.g. .NET defaults to UTF-16LE.

binascii.unhexlify(data), I jusf learned about AES encryption laat night and I'm using this line as the "normal" thing to do. Does it apply to my case?

Yes, because you've been given hexadecimals that represent the bytes given. There is a strong incentive for many developers to convert things to string, but in real protocols the ciphertext doesn't need to be text and can be processed as bytes (files, sockets, HTTP, FTP etc. all handle binary just fine).

I'm not sure if the data or key is Hex or Base64. The key is 64 characters so I assume it's Hex.

Well the most important thing is that base 64 necessarily has 64 characters to represent 6 bits each. So if you only see digits and A to F in upper- or lowercase then it is probably hexadecimals.