[Resolved] Recovering a ThreemaID from TWRP backup without root

For everyone who has lost his ThreemaID because of damaged phone, here is my solution.
All you need is an old TWRP/Nandroid backup that contains the data partition of your phone (you should have installed Threema before you backed up the data :p ) and a software like 7Zip (on Windows) or tar (on Linux).

1. Copy the TWRP/Nandroid files to your computer. On my XPeriaZ5 they are named from data.ext4.win000 to data.ext4.win006. These files are normal ".tar.gz" files. Rename them to data.ext4.win000.tgz … data.ext4.win006.tgz.
2. Use 7Zip or tar to browse the archive and navigate to "/data/data/ch.threema.app/files/".
3. Inside this directory, you will find a file named "idbackup.txt".
4. Extract and open this file. It contains your ThreemaID in plain text format.
5. Start Threema on your new (unrooted) phone and tell Threema to restore your ID from text.
6. Enter the long code you found in idbackup.txt (you will be asked for your password)
7. Feel happy