The company says the FBI is asking them to do something that would mean all current iPhones are breakable by law enforcement.
A senior Apple executive today confirmed that the custom software tool the FBI has ordered it to develop in order to crack into a dead terrorist's iPhone 5c would be effective on every type of iPhone currently being sold.
The fact that the software tool would work on all phones is part of the fundamental problem with the FBI's approach, the executive said during a call with journalists. The call was on the record, but journalists were asked not to name the executive or quote directly.
Experts had been speculating as to whether the software tool, which would override protections against a brute-force password-guessing attack, would apply to newer phones that have enhanced security features.
The phone in question is an iPhone 5C running iOS9. This is key because it's missing the extra privacy protection provided by the Secure Enclave, a feature that became available on iPhones starting with the 5S in 2013 but which was missing from the cheaper 5C.
The Secure Enclave is a physically separate computer in the phone that has control over sensitive features including Apple Pay, TouchID, and the keys that encrypt iMessages and keys that encrypt the phone's data. It was therefore possible that phones with the Secure Enclave would be resistant to a tool developed to break into the 5C; Apple is now saying that's not the case.
The FBI had asked Apple to "provide modified software" in order to hack into the phone, which belonged to Syed Rizwan Farook, one of two terrorists who died after an attack in San Bernadino, California that killed 14 people.
Apple said today that yes, the FBI's request is within its capabilities, but that the request is unduly burdensome. The executive said that Apple has not fully scoped out the project, but that it would take on the order of several weeks or several months. The executive noted that the request means not just writing the software, but validating it to ensure it doesn't break something else on the phone. The executive also speculated that if the FBI's order is granted, Russian and Chinese authorities will be quick to make similar requests.