Congratulations, you've invented the iMessage security model. The cryptographers behind signal are very smart; they have thought about these things. The signa

Congratulations, you've invented the iMessage security model. The cryptographers behind signal are very smart; they have thought about these things. The signal model has the advantage of not having to trust a third party server. With iMessage, it's possible for the government to force Apple to add pubkeys to a user's identity (although the user will be notified).