[nicolas_17]

> It’s not really designed to be an encryption system as much as it is a text message system that happens to include encryption.

And yet, Apple uses this (flawed?) encryption in lots of other features. It's not a messaging platform that happens to include encryption, it's a messaging platform (iMessage/Madrid) built on top of a generic/reusable encryption system (IDS), and many other Apple protocols are built on top of IDS. Apple's "platform security guide" has several places where they recognize this:

"When a user signs in to iCloud on a second Handoff-capable device, the two devices establish a Bluetooth Low Energy (BLE) 4.2 pairing out-of-band using APNs. The individual messages are encrypted much like messages in iMessage are."

"When an incoming call arrives, all configured devices are notified using the Apple Push Notification service (APNs), with each notification using the same end-to-end encryption as iMessage."