I do like obsidian. And I hope for much more features in the future (but there is already many).
In the current beta for the iOS app it seems I can only store the vault at a specific iCloud section.
It would be great to store it anywhere through the „files“ app in iOS.
In addition :
as user I want to be able to place the vault in the folder that BoxCryptor then encrypts on iCloud. This way I could use obsidian in conjunction with BoxCryptor (which simply end to end encrypts the information) and uses iCloud to sync across all my devices. (Apple). BoxCryptor Supports many cloud providers for its encryption. Not only iCloud.
BoxCryptor has an API and offers developer kits … maybe some specialists could have a look into it?! Would be a very unique selling point for obsidian: full support for user side privacy.
I primarily use Obsidian using the desktop apps as my vaults are in a Boxcryptor volume and stored on Dropbox. The ability for Obsidian mobile to access vaults managed by Boxcryptor via the Files App on iOS would allow me to bring the Obsidian experience to mobile, and would be greatly appreciated.
The “zero knowledge” is on their part/server, not about how your data is stored once reaches your phone/computer. Yes, Obsidian sync is E2EE sync solution.
Regarding encryption in your phone. Modern phones are already encrypted. You need your password (and/or) firgerprint not just to unlock the phone but to obtain a key used to decrypt it (this is all invisible to the user)
On Android, MAYBE there are some apps that let you mount an encrypted container to a directory of the filesystem and then obsidian could you that. (Much like veracrypt works on windows.)