Apple made sudden security changes to its chips in the fall of 2020

Apple made unusual hardware changes to the A12, A13 and S5 processors in its devices in the fall of 2020 to update the Secure Storage Component, according to Apple Support documents.

According to an Apple Support page, noted by Twitter user Andrew PantyukhinApple changed the Secure Enclave in a number of products in the fall of 2020:

Note: A12, A13, S4 and S5 products first released in Fall 2020 have a 2nd Generation Secure Storage Component; while previous products based on these SoCs have a first generation Secure Storage Component.

The Secure Enclave is a coprocessor used for data protection and authentication with Touch ID and Face ID. The purpose of the Secure Enclave is to process keys and other information, such as biometric data, that is sensitive enough not to be processed by the application processor. This data is stored in a Secure Storage Component in the Secure Enclave, the specific component that Apple changed last year.

At the very least, the explanation in Apple’s support document suggests that the eighth-generation entry-level iPad, Apple Watch SE, and HomePod mini have different Secure Enclaves compared to older devices with the same chip.

However, there are a number of differences in Apple’s support document. Despite Apple explaining that A13 products “first released in the fall of 2020 have a 2nd generation Secure Storage Component,” there was no device with an A13 chip that was “first released in the fall of 2020.” The last device that came out with an A13 chip was the iPhone SE in February 2020.

In fact, if the change were to be made to all newly produced devices with these chips, the affected devices would be the iPhone XR, iPhone 11, iPhone SE, and the fifth generation iPad mini, as well as the newly released eighth generation iPad, Apple Watch SE. and “HomePod mini”.

To make matters more confusing, the table listing the multiple versions of the Secure Enclave’s storage component in the summary of functions omits the S4 chip with a second-generation Secure Storage Component, despite the rubric claiming that a such a chip exists. The Apple Watch Series 4 was the only device to include an S4 chip, and this device was discontinued in September 2019, long before the second-generation Secure Storage Component was rolled out in the fall of 2020. It is possible that part of this lack of clarity relates to the fact that the A12 and S4 chips introduced the first generation Secure Storage Component.

New devices with the A14 or S6 chip, such as the iPhone 12, iPhone 12 Pro, iPad Air of the fourth generation, and Apple Watch Series 6, also have the updated Secure Enclave.

Although the change took place in the fall of 2020, the support document with detailed information about the change was published in February 2021. The full PDF version of Apple’s Platform Security Guide reveals the difference between the first and second generation Secure Storage Component:

The 2nd generation Secure Storage Component adds counter lockboxes. Each counter lockbox stores a 128-bit salt, a 128-bit passcode verifier, an 8-bit counter, and an 8-bit maximum attempt value. Access to the counter lockboxes is via an encrypted and verified protocol.

Counter lockboxes contain the entropy required to unlock password-protected user data. To access the user data, the associated Secure Enclave must derive the correct passcode entropy value from the user’s passcode and the Secure Enclave’s UID. The user’s passcode cannot be learned using unlock attempts sent from a source other than the associated Secure Enclave. If the passcode attempt limit is exceeded (for example, 10 attempts on iPhone), the password-protected data will be completely erased by the Secure Storage Component.

This appears to be a countermeasure against password-cracking devices, such as GrayKey, that try to break into iPhones by guessing the passcode an infinite number of times, using exploits that allow for infinite incorrect password attempts.

The change appears to have been significant enough to Apple to warrant a full “second generation” version of the Secure Enclave’s storage. It’s certainly unusual for Apple to change a component in its chips mid-production, but Apple likely thought the security upgrade was important enough to roll it out to all relevant new devices from the fall, rather than just devices running the latest A14. and S6 chips.