tl;dr More encryption.

So to a large extent the 'new' feature Apple is touting in iOS 8 is simply that they're encrypting more data. But it's also worth pointing out that newer iOS devices -- those with an "A7 or later A-series processor" -- also add substantial hardware protections to thwart device cracking.In the rest of this post I'm going to talk about how these protections may work and how Apple can realistically claim not to possess a back door.