[criddell]

I don't think so but I'm not a security expert either so I might have this wrong.

If you send a group message, Apple provides your messaging client with all of the recipients' public keys that are used to encrypt the symmetric key that actually protects the message. They could slip their key into that list and I don't think you would be able to easily tell if they did that.

If you send a message to a single person, then that's just a group of one.

The interesting question to me is if Apple can be compelled to write code to do this if they haven't already done so (and I don't think they have). I wouldn't think they could be forced, but like Microsoft did with Skype, they might do it anyway.