code: def decode_aes256_base64_auto(data, encryption_key):
      
      assert isinstance(data, bytes)
      length = len(data)
  
      if length == 0:
          return b''
      elif data[0] == b'!'[0]:
          return decode_aes256_cbc_base64(data, encryption_key)
      else:
          return decode_aes256_ecb_base64(data, encryption_key)
docs: Guesses AES cipher (EBC or CBD) from the length of the base64 encoded data.