Is it possible to tell if a 3DS had CFW installed and then uninstalled? Wondering specifically about Luma3DS + boot9strap. Thanks in advance
Usually yes. GodMode9 embeds important stuff, including NAND encryption keys. When opening GodMode9 on a console that has never seen CFW before, you'll get asked if you want to create this backup. This nag appears every time ǴodMode9 is started… until you allow it.
SYSNAND CTRNAND might contain (deleted) firm files. Dumping the NAND and scanning the partition with data recovery software while mounted with the help of ninfs should reveal this.
The ticket database might contain homebrew titles (I guess Format System Memory gets rid of those).
The time offset can be set to 0 (if battery not removed after uninstalling)
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If done with good preparation it should be impossible to tell CFW usage. Starting with a virgin 2|3DS console:
- ntrboot into GodMode9 → answer "No" to creating the embedded backup
- Backup the NAND (all virgin)
- Install B9S/FastBoot3DS with GodMode9 or boot into SafeB9SInstaller/OpenFirmInstaller
- Store this virgin backup in a secure location
- Complete the finalizing steps like normal
- Answer "Yes" next time GodMode9 asks for embedded backup
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If full uninstallation is desired, restore the virgin backup (full/forced restore).
If something goes wrong here (image damaged, console turned off, restore interrupted), the console might be fully bricked (worst case:
8046 Bootrom error) to a point where only ntrboot allows repairing the software.
I advise against full/forced NAND restore.
Remove battery to get rid of time offset nullification.