Security of iCloud Backup
The following content is backed up using iCloud Backup:
Records for purchased music, movies, TV shows, apps, and books. A user’s iCloud Backup includes information about purchased content present on the user’s device, but not the purchased content itself. When the user restores from an iCloud Backup, their purchased content is automatically downloaded from the iTunes Store, the App Store, the Apple TV app, or Apple Books. Some types of content aren’t downloaded automatically in all countries or regions, and previous purchases may be unavailable if they have been refunded or are no longer available in the store. Full purchase history is associated with a user’s Apple ID.
Photos and videos on a user’s devices. Note that if a user turns on iCloud Photos in iOS 8.1 or later, iPadOS 13.1 or later, or OS X 10.10.3 or later, their photos and videos are already stored in iCloud, so they aren’t included in the user’s iCloud Backup.
Contacts, calendar events, reminders, and notes
Home Screen and app organization
Medical ID data
Visual Voicemail password (requires the SIM card that was in use during backup)
iMessage, Apple Messages for Business, text (SMS), and MMS messages (requires the SIM card that was in use during backup)
When Messages in iCloud is enabled, iMessage, Apple Messages for Business, text (SMS), and MMS messages are removed from the user’s existing iCloud Backup and are instead stored in an end-to-end encrypted CloudKit container for Messages. The user’s iCloud Backup retains a key to that container. If the user later disables iCloud Backup, that container’s key is rolled, the new key is stored only in iCloud Keychain (inaccessible to Apple and any third parties), and new data written to the container can’t be decrypted with the old container key.
The key used to restore the messages in iCloud Backup is placed in two locations, iCloud Keychain and a backup in CloudKit. The backup in CloudKit is done if iCloud Backup is enabled and unconditionally restored whether the user restores an iCloud backup or not.