Let me know if you have any feedback about this article 😁
I don’t know the exact reason why Android requires the primary user to enter their PIN/password before any other user can log in, but it may be due to the fact that the primary user is also the “system” user which is “always running even when other users are in the foreground.
Full disk encryption?
Android hasn't used FDE for a couple of years now. File Based Encryption (FBE) has been required instead since Android 10. With FBE, each user has their own credential encrypted storage location for apps, which are encrypted with the credential from that particular user. (I verified this while testing. When you boot and unlock the primary user, other users data at /data/user/{id} is still encrypted until you unlock them.)
Maybe there are other system files required that are encrypted with the primary user credentials
There might be, though I couldn't find any. I poked around /data on a rooted Pixel that had just booted but hadn't had its primary user unlocked yet, and I was able to access most files in /data/system still.
Pretty much my thoughts, yes.
In order for the FDE to have any usefulness, the key has to be derived from a secret that only the user of phone knows (I.e. a secret PIN, password or pattern)
Android devices stopped using FDE a while back. In fact, support for FDE was removed entirely in Android 13.
Sorry, but that's not true. While technically true, that full disk encryption doesn't exist anymore, they use file based encryption which, functionally, is the same thing. Source: https://www.androidauthority.com/how-to-encrypt-android-device-326700/
File based encryption is not functionally "the same thing". The AOSP documentation explains how FBE works much more accurately.
I didn't know that Samsung had that feature, but it does sound nice - so long as you have the ability to enable maintenance mode.
I recently took my pixel 7 in to ubreakifix for a screen replacement. The screen was 100% dead, but I could still hear the notifications coming in. I couldn't put it into maintenance mode if it had one, so I think I'd still stress a bit about whether or not the phone would be wiped, such as in the case I was unable to verify the upload of a recent Aegis backup. It would be nice if the maintenance mode was able to be triggered via a web interface in cases such as mine. Or maybe even a specific button combo that would be difficult to accidentally do.
That's a good point, and I agree: There should be a way to trigger Maintenance Mode remotely, like through Find My Device, should Google implement this.
Good article, thanks for writing and sharing here!
I'm not an Android developer, but I do know Linux, and it sounds like Samsung's maintenance mode could just be another user with different permissions, with access to system directories but not user home directories.
If, as you say, Google gives the primary user full rights (like having admin rights in Windows), that would mean that Samsung might be creating "regular" users without those rights, and "maintenance mode" could simply be another regular user - by default, regular users don't have access to other regular user's home directories.
Theoretically, isn't maintenance mode completely useless?
If they're the manufacturer, they could upload and boot via fastboot a signed image that allows all tests to be done, all automatically
When I broke the screen of my Xiaomi mix 3, it was completely black, I sent it back to repair and they had no problem at all repairing it even if I didn't unlock it before sending it. (Maybe it's because Xiaomi has hw tests shortcuts in the bootloader?)
Sure, the manufacturer could, but they might not provide those kinds of images to their official repair centers, certainly not third-party ones.
Google should be embarrassed at how much better Samsung is.
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