Nobody really knows how the FBI is hacking into iPhones.

Well nobody, except Cellebrite and the FBI themselves.

We can safely assume that the underlying crypto wasn’t hacked–that would be truly catastrophic for everyone’s security, and way above the pay grade of a company like Cellebrite.

So we have to conclude that somehow the FBI has managed to trick the iPhone into giving up it’s encryption keys, or bypassed the Passcode protections on the phone. Apparently the hack doesn’t work on iPhone 5S and higher devices,  and obviously this can’t be a software bypass (because all iOS devices literally run the software), so it has to be a hardware limitation, one that probably affects the key storage.