After a lot of researching, I settled on using Boxcryptor for encrypting some files to upload to OneDrive. I am pretty comfortable with how it works on my Windows PC. However, I also installed the iOS app and it does give me a couple of security and privacy concerns.
First, I understand that the Boxcryptor app must be given access to OneDrive, but the setup also involved granting permission to access OneDrive as a whole, as the warning/permission mentioned even contacts. To what extent can Boxcryptor access OneDrive (which is tied to my entire Microsoft account, including e-mail)?
Second, to what extent are files made vulnerable by the iOS app cache? As I understand it, unencrypted files are cached for use by other apps? In my case, since I will not use the Boxcryptor app frequently, I log in, use the app, then log out completely (which I might not do if there was an app PIN). Does that minimize the risk of unencrypted files being obtained by someone who gets access to my device?