encrypted special backups are unencrypted or cannot restore

[TjrGithub]

The special backups don't behave as expected if backups are encrypted. They are mostly unencrypted, or cannot be restored, or are incomplete.

Tested: accounts, android, appwidgets, bluetooth, data.usage.policy, wallpaper, and wifi.access.points.

However, user app backups are encrypted correctly (tested with mupdf) and can be restored.

Steps to reproduce:

• install everthing (see below)
• create a new key in openkeychain (and nothing else)
• activate encryption in oandbackup preferences
• backup the special backups (data-only)
• try to open the backups with Amaze file explorer and with Openkeychain

Expected result: Amaze should find a PGP message inside the backup files. Openkeychain should detect a valid encrypted zip file and decrypt it correctly.

Observed results: accounts: decrypted file is 0 bytes long. Openkeychain shows unknown file name, but no error message. android: .zip is unencrypted, readable Amaze appwidgets: openkeychain decrypts the xml file directly, not signed, no .zip container bluetooth: decrypted .zip is 0 bytes long. Openkeychain shows unknown file name, but no error message. data.usage.policy: openkeychain decrypts both xml files directly, not signed, no .zip container. The .zip file, known from unencrypted oandbackup backups, is missing. wallpaper: .xml is unencrypted, readable Amaze wifi.access.points: openkeychain decrypts the xml file directly, not signed, no .zip container

Versions:

• lineageos-with-microg 15.1 as of 2019-04-10 with addon_root on a Mido
• xposed 90-beta3 and xprivacylua 1.24 FDroid, don't restrict oandbackup
• oandbackup 0.3.5-universal Fdroid
• openkeychain 5.2 Fdroid