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

Apple made unusual mid-production hardware changes to the A12, A13 and S5 processors in its devices in the fall of 2020 to upgrade the secure storage component, according to Apple support documents.

According to an Apple support page, noticed by the Twitter user Andrew Pantyukhin, Apple changed the Enclave Secure into a series of products in the fall of 2020:

Note: A12, A13, S4 and S5 products launched for the first time in autumn 2020 have a second-generation secure storage component; while previous products based on these SoCs have a generation I secure storage component.

Secure Enclave is a coprocessor that is used to protect and authenticate data with Touch ID and Face ID. The purpose of the Secure Enclave is to manage keys and other information, such as biometrics, that are sensitive enough not to be handled by the Application Processor. This data is stored in a secure storage component inside the Secure Enclave, which is the specific part that Apple changed last year.

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

However, there are a number of discrepancies in Apple’s support document. Despite Apple explaining that A13 products “first launched in the fall of 2020 have a second-generation secure storage component”, there was no device with an A13 chip “launched for the first time in the fall of 2020”. The last device launched with an A13 chip was the iPhone SE in February 2020.

If the change were, in fact, made to all new devices made with these chips, the affected devices would include iPhone XR, iPhone 11, honeiPhone SE‌ and iPad mini of the fifth generation, as well as the new version of the eighth generation ‌iPad‌, ‌Apple Watch SE‌ and ‌HomePod mini‌.

To make things more confusing, the table that lists several versions of the Secure Enclave storage component in the feature summary omits the S4 chip with a second-generation secure storage component, despite the heading that such a chip exists. The Apple Watch Series 4 was the only device to contain an S4 chip, and this device was discontinued in September 2019, long before the second-generation Secure Storage component was implemented in the fall of 2020. Some of this may be missing. clarity refers to the fact that the A12 and S4 chips introduced the first generation secure storage component.

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

Although the change took place in the fall of 2020, the support document detailing the change was released in February 2021. The full PDF version of the Apple Platform Security Guide reveals the difference between the first and second generation secure storage component:

The second-generation secure storage component adds lock boxes. Each meter lock box stores a 128-bit salt, a 128-bit password checker, an 8-bit counter, and a maximum of 8 test bits. Access to the meter lock boxes is through an encrypted and authenticated protocol.

The meter lock boxes have the entropy required to unlock password-protected user data. To access user data, the associated secure enclave must obtain the correct entropy value of the access code from the user access code and the secure enclave UID. The user access code cannot be learned using unlock attempts sent from a source other than the associated Enclave Secure. If the passcode test limit is exceeded (for example, 10 attempts on iPhone), the passcode-protected data is completely erased by the Secure Storage Component.

This seems to be a countermeasure against password cracking devices, such as GrayKey, which tries to enter iPhones by guessing the access code several times, using exploits that allow incorrect password attempts.

The change seems to have been significant enough for Apple to justify an entire “second generation” version of the Secure Enclave’s storage space. It’s certainly unusual for Apple to change a component of its chips in the middle of production, but Apple probably thought the security update was important enough to launch on all relevant new devices starting in the fall, rather than for devices with the most recently A14 and S6 chips.