Restoring the backup of an encrypted phone

Question

I had an LG G2, running LineageOS 7.1 with enabled encryption. I took regular backups using TWRP 3 (which can deal with encryption).

The phone broke. I now want to restore the backup using TWRP on a new LG G2.

How can I restore the backup from the old phone using encryption onto the new phone (no encryption yet)?

I tried to restore the backup as-is and it doesn't boot (black screen). Anything special that I need to do before restoring?

Should I first encrypt the new phone and then restore the backup? Or do I need to strip the encryption from the backup somehow before restoring it?

Answer 1

As it turns out, TWRP/nandroid backups aren't encrypted. The encryption layer sits lower at the level of the device.

You can therefore restore the backup on a new device like any other backup simply by using the restore function in TWRP. You have to re-enable encryption afterwards, of course.

This also means that backup data is not encrypted and therefore must be protected in storage. I've never read this anywhere; be aware of the security implications.

Edit: The reason for the above mentioned boot problem was unrelated to the backup. I had the wrong bootstack on the new phone and first needed to upgrade to the most recent stock rom.

Answer 2

There's no reason as to why the device won't turn on at all if it's of the same exact model as the backed up one. Unless if the twrp backup got corrupt and you restored ignoring the message digest check (MD5). Remember before accessing TWRP if device is encrypted, TWRP asks for decryption password to decrypt data hence you copied files after it's decryption. There's no need to even think about encryption. Just if the backup doesn't work, and I'm sure you have TWRP, grab a freshly downloaded lineage and flash it to device. It's better to have a working phone with your data lost than having a bricked one