Encrypted cloud backup on Android

Hello,

Like many people, I have many files (text, pictures, ...) on my Android smartphone; Files I don't want to lose. I could use Google Drive or similar software to have a copy of files in the cloud in case my smartphone is destroyed/lost/stolen, but files would be stored unencrypted server-side, so we don't want that. I'm looking for an E2EE solution to have a copy of the files in my phone on some cloud.

A common situation : you are on holidays, you only have your phone with you (no computer…). Near the end of the holidays, you break/lose your phone (or your backpack with your computer and phone is stolen). If your files are not synced/backed up in some cloud, you lose all your more recent files (including holidays pictures).

I searched for solutions, but found nothing good so far.

• I considered Cryptomator for Android, but after 5,5 years the Document Provider API is still not implemented, despite the promises of the developers (they didn't bother with a roadmap for 2023 for Cryptomator, it's half abandoned with only cosmetic/bug fixes updates). There is no support for automation tools neither. So it does not seem appropriate.
• Maybe a local encryption app, combined with a standard cloud sync app, could do the trick, but I have not found an efficient solution yet.

I'd like to know how you solved this problem for yourselves, or if you have any advice. It seems to be a common use case, I think it can be useful to many people.

note: I use Syncthing on a day-to-day basis to sync my files between my devices, but it won't help in these situations.

(I hope my English is not too bad, it's not my mother tongue, sorry)