Apple's announcement itself:
"Unlike our competitors, Apple cannot bypass your passcode and therefore cannot access this data. So it's not technically feasible for us to respond to government warrants for the extraction of this data from devices in their possession running iOS 8."
https://www.apple.com/privacy/government-information-request...
"Specifically, Apple has radically improved the way that data on those devices is encrypted. Once users set a passcode, Apple will no longer be able to unlock your device—even if ordered to do so by a court."
http://www.slate.com/articles/technology/future_tense/2014/0...
"To get started, it's worth pointing out that disk encryption is hardly new with iOS 8. In fact, Apple's operating system has enabled some form of encryption since before iOS 7. What's happened in the latest update is that Apple has decided to protect much more of the interesting data on the device under the user's passcode.
...
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 ... 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."
http://blog.cryptographyengineering.com/2014/10/why-cant-app...