Apple quietly introduced code into iOS 18.1 which reboots the device if it has not been unlocked for a period of time, reverting it to a state which improves the security of iPhones overall and is making it harder for police to break into the devices, according to multiple iPhone security experts.
On Thursday, 404 Media reported that law enforcement officials were freaking out that iPhones which had been stored for examination were mysteriously rebooting themselves. At the time the cause was unclear, with the officials only able to speculate why they were being locked out of the devices. Now a day later, the potential reason why is coming into view.
“Apple indeed added a feature called ‘inactivity reboot’ in iOS 18.1.,” Dr.-Ing. Jiska Classen, a research group leader at the Hasso Plattner Institute, tweeted after 404 Media published on Thursday along with screenshots that they presented as the relevant pieces of code.
Why does rebooting it improve the safety or security of the phone?
Once rebooted, you need to enter your PIN to unlock the phone (and the SIM as well). Before that it is not possible to unlock the phone with biometric credentials (face ID or fingerprint).
As far as I’m aware, police can force you to hand over your biometric credentials (they can hold the phone to your face to unlock it when you have face ID enabled, or can move your finger to the fingerprint sensor). But they can’t force you to reveal the PIN number.
BFU (before first unlock) vs AFU (After first unlock)
Basically encrypted vs decrypted
As I understand it, even though after Reboot the OS looks like its in about the same state with the wallpaper and same password to unlock, the fact that it hasn’t been unlocked yet means that certain attacks don’t work as well. I don’t know why specifically. I think it’s because the attack may still work but doesn’t reveal any sensitive data because it’s just the ROM, wallpaper, sim, etc.
Most likely after rebooting but before unlocking the decryption key is not present in memory in plaintext.