I have noticed that my iCloud backup on iOS is increasing in size in line with all files I encrypt with Boxcryptor. This is across various different cloud providers not just what I have on iCloud itself, which is very little. I am now wondering if all of the data in Boxcryptor for iOS is being backed up in iCloud, in which case data from across all of my cloud services is not end-to-end encrypted as Apple has the key.