Summary

Anti Savegame Restore is a feature originally implemented in FS module with 4.0.0-7, which prevents the user from restoring previous versions of a savegame image(mainly for SD saves). This feature is not used for gamecard games. When an old version of the save is detected, the application will display an error regarding old savegame version, then delete+recreate the save(similar to when the savegame is corrupted).

Implementation

When creating the SD savedata, the application generates a random u64 value, then stores it in an arbitary savefile in the savegame FS. The application then uses the anti-savegame-restore FS commands to verify the stored u64(with the u64 loaded by FS module), and to update the u64 used by FS module. The u64 used by FS module is stored in a NAND savegame.

Each time the application writes to the savegame, the u64 value stored in the savefile should be updated(and the command for updating the NAND u64 value should be used as well). Usually applications update this value by incrementing it, however generating a new random-number or other methods of updating it can be used as well.

Applications using this feature

Animal Crossing: New Leaf
Pokemon X & Y (unknown if this feature actually used for this currently)

It's currently unknown whether there's any eShop-only titles that use this.

Applications which use this feature have had a Product Code of "CTR-x-Exxx", obviously the "E" in that part of the product code doesn't trigger this feature, but it may be an internal reference for Nintendo for easy identification of such games.