public string BuildMessage(string msg, string token)
{
var key = Md5(token);
var iv = Md5($"{key}{token}");
var encryptedData = CryptoProvider.EncryptData(iv.ToByteArray(), key.ToByteArray(), Encoding.UTF8.GetBytes(msg)).ToHex();
var dataLength = (encryptedData.Length / 2 + 32).ToString("x").PadLeft(4, '0');
var checksum = Md5($"{_magic}{dataLength}{_unknown1}{_deviceType}{_serial}{_time}{token}{encryptedData}");
return($"{_magic}{dataLength}{_unknown1}{_deviceType}{_serial}{_time}{checksum}{encryptedData}");
}