code: def old_decode_aes(key, iv_plus_encrypted):
      
      # grab first 16 bytes (aka 32 characters of hex) - that's the IV
      hexed_iv = iv_plus_encrypted[:32]
      # grab everything else - that's the ciphertext (aka encrypted message)
      hexed_ciphertext = iv_plus_encrypted[32:]
      # unhex the iv and ciphertext
      iv = binascii.unhexlify(hexed_iv)
      ciphertext = binascii.unhexlify(hexed_ciphertext)
      # set up the correct AES cipher object
      cipher = AES.new(ensure_bytes(old_pad(key)), mode=AES.MODE_CBC, IV=iv)
      # decrypt!
      plaintext = cipher.decrypt(ciphertext)
      # return the unpadded version of this
      return old_unpad(plaintext)
docs: Utility method to decode a payload consisting of the hexed IV + the hexed ciphertext using
      the given key. See above for more details.
  
      :param key: string, <= 32 bytes long
      :param iv_plus_encrypted: string, a hexed IV + hexed ciphertext