Encrypting save games

Why?

Because the world today is not the world of yesterday. A capitalist oligarchy runs the world and forces us to consume in order to keep the gears of this rotten society on track. As such, the biggest market for video game consumption today is the mobile one. It is a market of poor souls forced to compulsively consume digital content in order to forget the misery of their everyday life, commute, or just any other brief free moment they have that they are not using to produce goods or services for the ruling class. These individuals need to keep focusing on their video games (because not doing so will fill them with tremendous existential angst), so they go as far as spending money on them to extend their experience, and their preferred way of doing so is through in-app purchases and virtual currency.

But what if someone were to find a way to edit the saved games and assign the items and currency without effort? That would be terrible, because it would help players consume the content much faster, and therefore run out of it sooner than expected. If that happens, they will have nothing that avoids them to think, and the tremendous agony of realizing their own irrelevance would again take over their life.

No, we definitely do not want that to happen, so let’s see how to encrypt savegames and protect the world order.

How?

The class File can open a file at a location and read/write data (integers, strings and variants). It also supports encryption. To create an encrypted file, a passphrase must be provided, like this:

GDScript

C#

var f = File.new()
var err = f.open_encrypted_with_pass("user://savedata.bin", File.WRITE, "mypass")
f.store_var(game_state)
f.close()

var f = new File();
var err = f.OpenEncryptedWithPass("user://savedata.bin", (int)File.ModeFlags.Write, "mypass");
f.StoreVar(gameState);
f.Close();

This will make the file unreadable to users, but will still not prevent them from sharing savefiles. To solve this, use the device unique id or some unique user identifier, for example:

GDScript

C#

var f = File.new()
var err = f.open_encrypted_with_pass("user://savedata.bin", File.WRITE, OS.get_unique_id())
f.store_var(game_state)
f.close()

var f = new File();
var err = f.OpenEncryptedWithPass("user://savedata.bin", (int)File.ModeFlags.Write, OS.GetUniqueId());
f.StoreVar(gameState);
f.Close();

Note that OS.get_unique_id() does not work on UWP or HTML5.

That is all! Thank you for your cooperation, citizen.

Note

This method cannot really prevent players from editing their savegames locally because, since the encryption key is stored inside the game, the player can still decrypt and edit the file themselves. The only way to prevent this from being possible is to store the save data on a remote server, where players can only make authorized changes to their save data. If your game deals with real money, you need to be doing this anyway.