Writing secure data to a protected file

[Maxim DC]

Hello everyone,
I was making an application today and noticed that i only can save files like this localy

QByteArray txtBuffer = "txtdata";
QFile file("file.txt");
if (file.open(QIODevice::WriteOnly))
{
	file.write(txtBuffer);
	qInfo() << "[Info] Txt has been written to the disk";
}
file.close();

and read it like this

QByteArray txtBuffer;
QFile file("file.txt");
if (file.open(QIODevice::ReadOnly))
{
	txtBuffer = file.readAll();
	qInfo() << "[Info] Txt has been read from the disk";
}
file.close();

but what if that data isn't that stupid like "txtdata" but something more like progress in a game, how to save this? I could do it like this but then the player can just alter the progress in the game with a text-editor so it has more abilities or something like that. I would like to prevent this by writing to a protected location or a password-protected file, especially on Android. What is the right approach?

[A Former User]

Hi! One simplistic approach that comes to my mind: Once you want to save the contents to your file.txt, take this content, append a secret string to it and compute a hash over everything. Then save the content (without the secret, of course) to a file. Also save the computed hash to another file. Next time, your application reads the two files, recomputes the hash and checks if they match.

[SGaist]

Hi,

Thinking of something like encrypting that file ?

The CryptFileDevice project might be of interest.

[the_]

@Maxim-DC

but what if that data isn't that stupid like "txtdata" but something more like progress in a game, how to save this?

Another approach for this could be QSettings with a custom format. You could set a reader and a writer function that writes encrypted data into a file.

QSettings::Format newformat = QSettings::registerFormat("cnf",read,write);
settings = new QSettings("cnf/u.cnf",newformat);

bool read(QIODevice &dev,QSettings::SettingsMap &map) {
   //your code goes here 
   return true;
}

bool write(QIODevice &dev,const QSettings::SettingsMap &map) {
   //your code goes here
  return true;
}

For not so strong encryption you could use Simple Crypt in your read and write functions