> "Specifically, the FBI wants us to make a new version of the iPhone operating system, circumventing several important security features, and install it on an iPhone recovered during the investigation. In the wrong hands, this software — which does not exist today — would have the potential to unlock any iPhone in someone’s physical possession."

So there is already a backdoor. Apple are refusing to let the FBI use the backdoor.

The backdoor is the fact that Apple can push a firmware update that disables security features, without the device's password being entered at any point.