Apple: No, We Can’t Read Your iMessages (And We Don’t Want to, Either)
Again, these key-based systems are the norm, and–as was pointed out in this article–other messaging systems were forced to comply with government orders to institute man-in-he-middle interceptions. It wouldn’t be impossible for Apple to do the same.
That said, I’d be interested to know how they implemented this to make interception difficult. Sharing that knowledge with the industry might make us all safer while adding validity to their claims.