Is there anything missing in an encrypted iPhone backup? As far as I understand iOS Security, Oct. 12, an encrypted backup via iTunes also backs up the keychain of the device. While I recognize that some elements might not be restorable onto a different device (non-migatory), I was wondering if anything substantial is actually missing in an encrypted backup.

I am asking this because I heard that after wiping an iPhone, the private key of the app Threema is lost and cannot be restored via backup, even on the same device.
Got answer from Threema support. The keys actually are included in an encrypt iTunes backup but can only be restored to the same device. That is why they advise a separate backup.


  Hello,
  
  Yes, encrypted iOS backups include the iOS keychain and therefore also
  the Threema private key; however as it is stored with
  kSecAttrAccessibleWhenUnlockedThisDeviceOnly, it will additionally be
  encrypted with the device-specific UID key. Therefore, it will only be
  usable if restored to the same device that the backup was created on.
  
  Best Regards,
  
  Threema Support