tl;dr: I have my Motorola Moto Z2 Play / A8.0 encrypted and I was forced to provide PIN during very early boot phase of my phone. Since about 1-2 weeks ago -- when my phone had a one-time accident of very long boot -- Android stopped asking for that PIN at boot time. How can my phone be still encrypted and no longer need that PIN to decrypt itself?
About 2-3 years ago I have encrypted my Motorola Moto Z2 Play (now with Android 8.0). I used the same PIN for the encryption process, so starting from that moment, I had to use PIN three times:
- boot (encryption)
- startup (SIM card PIN) and
- startup (fingerprint unlock).
About 1-2 weeks ago my phone hanged badly. After force-restarting, it needed about 20-30 minutes (!) to actually start.
From that moment on, I am no longer needed to enter PIN to decrypt phone and start Android. The first time, I now need to provide it, is when unlocking my SIM card.
My phone was not reset after that one-time very long boot accident. After it finally got up, I had everything in places: all apps, accounts, settings etc., nothing changed, reset or removed.
I have double-checked that my phone is still encrypted:
There was no system update (phone stays at Android 8.0.0 from 1+ year and probably forever), no new application installed and no change in system configuration for long months.
My phone uses fingerprint + PIN screen lock. PIN in numeric, four digit.
From this answer:
If the phone boots up without asking for a password, it is most likely not protected by encryption in the way you would expect. In theory, it might not be encrypted at all (...).
This answer explains that:
The best way to tell if your Android device is encrypted (and the encryption is actually in use) is to reboot it and see if it asks for a password/PIN with a prompt on a black screen that says: "To start Android, enter your PIN" (...) The lack of prompt means the master key is not encrypted".
I don't see such prompt, so I now know that my master key is not encrypted (while the file system itself seems to be encrypted -- above screenshot). But this answer does not explain how / why my master key was encrypted for 2-3 years and stopped being encrypted two weeks ago after a very long boot accident / force-reset.
So, why or when my Android 8.0.0 can decide to decrypt my master key and no longer need me to enter startup PIN to decrypt it?