[orastor]

Apple can also silently create a stealthy virtual device that will get all messages as your phone does

[Gaelan]

Unless you know something about the protocol that I don't (quite possible), it's not silent: all you devices get "new device registered to iMessage" dialog box.

[ronyfadel]

That’s a notification pushed by Apple I guess?

[shuckles]

Since Apple operates the key service and there is no key transparency mechanism, they could certainly do it (technically) with only a server side change.