In other words, for the extremely privacy-conscious, securing an iPhone with a passcode alone is actually a better choice than using Touch ID.
Best iPhone privacy measures: Secure Enclave
We'll be talking again about Apple's privacy battle with the FBI in more detail in a bit, but it's worth discussing one technical aspect of that case here. The iPhone belonging to one of the shooters in the San Bernardino case (or rather, belong to his employer) is a 5c model, and this - the company claims - is crucial in Apple's ability to open it up. iPhones more recent than this are equipped with security measures that mean even Apple's own engineers wouldn't be able to access the data inside.
As well as introducing Touch ID, the iPhone 5s was also the first iPhone to feature a security measure that Apple calls the Secure Enclave. This is an area of the processor chip - a separate processor in its own right, essentially - that stores the fingerprints and other security-critical data. But it is also a crucial part of the encryption setup.
"The Secure Enclave uses a secure boot system to ensure that it the code it runs can't be modified," explains Mike Ash, "and it uses encrypted memory to ensure that the rest of the system can't read or tamper with its data. This effectively forms a little computer within the computer that's difficult to attack."
(I'm obliged to Mike for virtually all of my understanding of the Secure Enclave's technicalities, but he acknowledges in turn that his findings partly derive from Apple's published security guide: the security measures mean that a lot of the Secure Enclave's details remain unverifiable.)
The generally agreed plan for Apple to break into the shooter's iPhone 5c involves the company's engineers creating and installing a custom build of iOS - one that doesn't have the same security measures that prevent brute-forcing of the passcode. The OS on the Secure Enclave, it is surmised, features defensive measures that would delete the keys to the encrypted data if new firmware were installed.
Apple is publicly committed to user privacy
Following the San Bernardino shootings of December 2015, the FBI obtained a warrant to search an iPhone 5c belonging to one of the shooters, Syed Rizwan Farook (the phone was technically the property of Farook's employers, which was a factor in obtaining permission to do this). Yet the FBI were unable to get into the device because it was locked with a passcode, and sought - and obtained - a court order instructing Apple to open the phone up.
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