Apple

Thanks for digging into this and confirming my understanding!

On a quick glance, this looks to be more secure the the old Hackintosh push notification (where it was based solely on a single device ID/serial number), but rather, some kind of certificate based identity system. This makes it more secure because without access to Apple's private signing keys, it should be very difficult to get a certificate signed by Apple to spoof the interaction. Though, I wonder how were the devices getting it in the first place, and if that part would be the next vector that'd need to be compromised (i.e.: if you get a signed certificate during device activation, then it'd be possible to swipe a signed certificate from a Mac you own; or that activation process itself becomes the next attack vector).

Having interacted very briefly with Eric Migicovsky a long time ago (due to Pebble), this does not surprise me that much. He's a great guy, and appears to want to do the right thing to help everyone. Beeper wanted to do it in the cloud with Mac systems/VMs, which is a costly endeavour. This POC would allow the interaction to run natively without themselves essentially MITM'ing all users, so it would save their company a lot of money. POC was done allegedly by some high school kid, and given Eric's Pebble fame, I think he's just thrilled that they could save some money and help some kid get started.

In all cases, it is certainly interesting to see how this has been playing out, and I'd be curious to see how this continue to play out, because I doubt this will be the end of this story.