Safe Enclave

Overview

The Safe Enclave is a devoted safe subsystem built-in into Apple techniques on chip (SoCs). The Safe Enclave is remoted from the primary processor to offer an additional layer of safety and is designed to maintain delicate person knowledge safe even when the Utility Processor kernel turns into compromised. It follows the identical design ideas because the SoC does—a boot ROM to determine a {hardware} root of belief, an AES engine for environment friendly and safe cryptographic operations, and guarded reminiscence. Though the Safe Enclave doesn’t embody storage, it has a mechanism to retailer info securely on hooked up storage separate from the NAND flash storage that’s utilized by the Utility Processor and working system.

The Secure Enclave components.The Safe Enclave parts.

The Safe Enclave is a {hardware} characteristic of most variations of iPhone, iPad, Mac, Apple TV, Apple Watch, and HomePod—specifically:

  • iPhone 5s or later

  • iPad Air or later

  • MacBook Professional computer systems with Contact Bar (2016 and 2017) that comprise the Apple T1 Chip

  • Intel-based Mac computer systems that comprise the Apple T2 Safety Chip

  • Mac computer systems with Apple silicon

  • Apple TV HD or later

  • Apple Watch Collection 1 or later

  • HomePod and HomePod mini

Safe Enclave Processor

The Safe Enclave Processor supplies the primary computing energy for the Safe Enclave. To supply the strongest isolation, the Safe Enclave Processor is devoted solely for Safe Enclave use. This helps forestall side-channel assaults that rely on malicious software program sharing the identical execution core because the goal software program beneath assault.

The Safe Enclave Processor runs an Apple-customized model of the L4 microkernel. It’s designed to function effectively at a decrease clock velocity that helps to guard it towards clock and energy assaults. The Safe Enclave Processor, beginning with the A11 and S4, features a memory-protected engine and encrypted reminiscence with anti-replay capabilities, safe boot, a devoted random quantity generator, and its personal AES engine.

Reminiscence Safety Engine

The Safe Enclave operates from a devoted area of the gadget’s DRAM reminiscence. A number of layers of safety isolate the Safe Enclave protected reminiscence from the Utility Processor.

When the gadget begins up, the Safe Enclave Boot ROM generates a random ephemeral reminiscence safety key for the Reminiscence Safety Engine. Every time the Safe Enclave writes to its devoted reminiscence area, the Reminiscence Safety Engine encrypts the block of reminiscence utilizing AES in Mac XEX (xor-encrypt-xor) mode, and calculates a Cipher-based Message Authentication Code (CMAC) authentication tag for the reminiscence. The Reminiscence Safety Engine shops the authentication tag alongside the encrypted reminiscence. When the Safe Enclave reads the reminiscence, the Reminiscence Safety Engine verifies the authentication tag. If the authentication tag matches, the Reminiscence Safety Engine decrypts the block of reminiscence. If the tag doesn’t match, the Reminiscence Safety Engine alerts an error to the Safe Enclave. After a reminiscence authentication error, the Safe Enclave stops accepting requests till the system is rebooted.

Beginning with the Apple A11 and S4 SoCs, the Reminiscence Safety Engine provides replay safety for Safe Enclave reminiscence. To assist forestall replay of security-critical knowledge, the Reminiscence Safety Engine shops a nonce for the block of reminiscence alongside the authentication tag. The nonce is used as an extra tweak for the CMAC authentication tag. The nonces for all reminiscence blocks are protected utilizing an integrity tree rooted in devoted SRAM inside the Safe Enclave. For writes, the Reminiscence Safety Engine updates the nonce and every stage of the integrity tree as much as the SRAM. For reads, the Reminiscence Safety Engine verifies the nonce and every stage of the integrity tree as much as the SRAM. Nonce mismatches are dealt with equally to authentication tag mismatches.

On Apple A14, M1, and later SoCS, the Reminiscence Safety Engine helps two ephemeral reminiscence safety keys. The primary is used for knowledge non-public to the Safe Enclave, and the second is used for knowledge shared with the Safe Neural Engine.

The Reminiscence Safety Engine operates inline and transparently to the Safe Enclave. The Safe Enclave reads and writes reminiscence as if it had been common unencrypted DRAM, whereas an observer outdoors the Safe Enclave sees solely the encrypted and authenticated model of the reminiscence. The result’s sturdy reminiscence safety with out efficiency or software program complexity tradeoffs.

Safe Enclave Boot ROM

The Safe Enclave features a devoted Safe Enclave Boot ROM. Just like the Utility Processor Boot ROM, the Safe Enclave Boot ROM is immutable code that establishes the {hardware} root of belief for the Safe Enclave.

On system startup, iBoot assigns a devoted area of reminiscence to the Safe Enclave. Earlier than utilizing the reminiscence, the Safe Enclave Boot ROM initializes the Reminiscence Safety Engine to offer cryptographic safety of the Safe Enclave protected reminiscence.

The Utility Processor then sends the sepOS picture to the Safe Enclave Boot ROM. After copying the sepOS picture into the Safe Enclave protected reminiscence, the Safe Enclave Boot ROM checks the cryptographic hash and signature of the picture to confirm that the sepOS is permitted to run on the gadget. If the sepOS picture is correctly signed to run on the gadget, the Safe Enclave Boot ROM transfers management to sepOS. If the signature isn’t legitimate, the Safe Enclave Boot ROM is designed to forestall any additional use of the Safe Enclave till the following chip reset.

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On Apple A10 and later SoCs, the Safe Enclave Boot ROM locks a hash of the sepOS right into a register devoted to this function. The Public Key Accelerator makes use of this hash for operating-system-bound (OS-bound) keys.

Safe Enclave Boot Monitor

On Apple A13 and later SoCs, the Safe Enclave features a Boot Monitor designed to make sure stronger integrity on the hash of the booted sepOS.

At system startup, the Safe Enclave Processor’s System Coprocessor Integrity Safety (SCIP) configuration helps forestall the Safe Enclave Processor from executing any code aside from the Safe Enclave Boot ROM. The Boot Monitor helps forestall the Safe Enclave from modifying the SCIP configuration immediately. To make the loaded sepOS executable, the Safe Enclave Boot ROM sends the Boot Monitor a request with the handle and dimension of the loaded sepOS. On receipt of the request, the Boot Monitor resets the Safe Enclave Processor, hashes the loaded sepOS, updates the SCIP settings to permit execution of the loaded sepOS, and begins execution inside the newly loaded code. Because the system continues booting, this identical course of is used every time new code is made executable. Every time, the Boot Monitor updates a operating hash of the boot course of. The Boot Monitor additionally consists of vital safety parameters within the operating hash.

When boot completes, the Boot Monitor finalizes the operating hash and sends it to the Public Key Accelerator to make use of for OS-bound keys. This course of is designed in order that working system key binding can’t be bypassed even with a vulnerability within the Safe Enclave Boot ROM.

True Random Quantity Generator

The True Random Quantity Generator (TRNG) is used to generate safe random knowledge. The Safe Enclave makes use of the TRNG every time it generates a random cryptographic key, random key seed, or different entropy. The TRNG is predicated on a number of ring oscillators publish processed with CTR_DRBG (an algorithm based mostly on block ciphers in Counter Mode).

Root Cryptographic Keys

The Safe Enclave features a distinctive ID (UID) root cryptographic key. The UID is exclusive to every particular person gadget and isn’t associated to every other identifier on the gadget.

A randomly generated UID is fused into the SoC at manufacturing time. Beginning with A9 SoCs, the UID is generated by the Safe Enclave TRNG throughout manufacturing and written to the fuses utilizing a software program course of that runs solely within the Safe Enclave. This course of protects the UID from being seen outdoors the gadget throughout manufacturing and subsequently isn’t accessible for entry or storage by Apple or any of its suppliers.

sepOS makes use of the UID to guard device-specific secrets and techniques. The UID permits knowledge to be cryptographically tied to a specific gadget. For instance, the important thing hierarchy defending the file system consists of the UID, so if the interior SSD storage is bodily moved from one gadget to a different, the information are inaccessible. Different protected device-specific secrets and techniques embody Contact ID or Face ID knowledge. On a Mac, solely totally inner storage linked to the AES engine receives this stage of encryption. For instance, neither exterior storage gadgets related over USB nor PCIe-based storage added to the 2019 Mac Professional are encrypted on this vogue.

The Safe Enclave additionally has a tool group ID (GID), which is widespread to all gadgets that use a given SoC (for instance, all gadgets utilizing the Apple A14 SoC share the identical GID).

The UID and GID aren’t accessible by way of Joint Take a look at Motion Group (JTAG) or different debugging interfaces.

Safe Enclave AES Engine

The Safe Enclave AES Engine is a {hardware} block used to carry out symmetric cryptography based mostly on the AES cipher. The AES Engine is designed to withstand leaking info by utilizing timing and Static Energy Evaluation (SPA). Beginning with the A9 SoC, the AES Engine additionally consists of Dynamic Energy Evaluation (DPA) countermeasures.

The AES Engine helps {hardware} and software program keys. {Hardware} keys are derived from the Safe Enclave UID or GID. These keys keep inside the AES Engine and aren’t made seen even to sepOS software program. Though software program can request encryption and decryption operations with {hardware} keys, it may possibly’t extract the keys.

On Apple A10 and newer SoCs, the AES Engine consists of lockable seed bits that diversify keys derived from the UID or GID. This permits knowledge entry to be conditioned on the gadget’s mode of operation. For instance, lockable seed bits are used to disclaim entry to password-protected knowledge when booting from System Firmware Replace (DFU) mode. For extra info, see Passcodes and passwords.

AES Engine

Each Apple gadget with a Safe Enclave additionally has a devoted AES256 crypto engine (the “AES Engine”) constructed into the direct reminiscence entry (DMA) path between the NAND (nonvolatile) flash storage and foremost system reminiscence, making file encryption extremely environment friendly. On A9 or later A-series processors, the flash storage subsystem is on an remoted bus that’s granted entry solely to reminiscence containing person knowledge by way of the DMA crypto engine.

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At boot time, sepOS generates an ephemeral wrapping key utilizing the TRNG. The Safe Enclave transmits this key to the AES Engine utilizing devoted wires, designed to forestall it from being accessed by any software program outdoors the Safe Enclave. sepOS can then use the ephemeral wrapping key to wrap file keys to be used by the Utility Processor file-system driver. When the file-system driver reads or writes a file, it sends the wrapped key to the AES Engine, which unwraps the important thing. The AES Engine by no means exposes the unwrapped key to software program.

Be aware: The AES Engine is a separate element from each the Safe Enclave and the Safe Enclave AES Engine, however its operation is intently tied to the Safe Enclave, as proven under.

The AES Engine supports line-speed encryption on the DMA path for efficient encryption and decryption of data is it is written and read to storage.The AES Engine helps line-speed encryption on the DMA path for environment friendly encryption and decryption of knowledge is it’s written and browse to storage.

Public Key Accelerator

The Public Key Accelerator (PKA) is a {hardware} block used to carry out uneven cryptography operations. The PKA helps RSA and ECC (Elliptic Curve Cryptography) signing and encryption algorithms. The PKA is designed to withstand leaking info utilizing timing and side-channel assaults equivalent to SPA and DPA.

The PKA helps software program and {hardware} keys. {Hardware} keys are derived from the Safe Enclave UID or GID. These keys keep inside the PKA and aren’t made seen even to sepOS software program.

Beginning with A13 SoCs, the PKA’s encryption implementations have been proved to be mathematically right utilizing formal verification methods.

On Apple A10 and later SoCs, the PKA helps OS-bound keys, additionally known as Sealed Key Safety (SKP). These keys are generated utilizing a mix of the gadget’s UID and the hash of the sepOS operating on the gadget. The hash is offered by the Safe Enclave Boot ROM, or by the Safe Enclave Boot Monitor on Apple A13 and later SoCs. These keys are additionally used to confirm the sepOS model when making requests to sure Apple providers and are additionally used to enhance the safety of passcode-protected knowledge by serving to to forestall entry to keying materials if vital modifications are made to the system with out person authorization.

Safe nonvolatile storage

The Safe Enclave is provided with a devoted safe nonvolatile storage gadget. The safe nonvolatile storage is related to the Safe Enclave utilizing a devoted I2C bus, in order that it may possibly solely be accessed by the Safe Enclave. All person knowledge encryption keys are rooted in entropy saved within the Safe Enclave nonvolatile storage.

In gadgets with A12, S4, and later SoCs, the Safe Enclave is paired with a Safe Storage Element for entropy storage. The Safe Storage Element is itself designed with immutable ROM code, a {hardware} random quantity generator, a per-device distinctive cryptographic key, cryptography engines, and bodily tamper detection. The Safe Enclave and Safe Storage Element talk utilizing an encrypted and authenticated protocol that gives unique entry to the entropy.

Units first launched in Fall 2020 or later are geared up with a 2nd-generation Safe Storage Element. The 2nd-generation Safe Storage Element provides counter lockboxes. Every counter lockbox shops a 128-bit salt, a 128-bit passcode verifier, an 8-bit counter, and an 8-bit most try worth. Entry to the counter lockboxes is thru an encrypted and authenticated protocol.

Counter lockboxes maintain the entropy wanted to unlock passcode-protected person knowledge. To entry the person knowledge, the paired Safe Enclave should derive the proper passcode entropy worth from the userʼs passcode and the Safe Enclaveʼs UID. The person’s passcode can’t be realized utilizing unlock makes an attempt despatched from a supply aside from the paired Safe Enclave. If the passcode try restrict is exceeded (for instance, 10 makes an attempt on iPhone), the passcode-protected knowledge is erased utterly by the Safe Storage Element.

To create a counter lockbox, the Safe Enclave sends the Safe Storage Element the passcode entropy worth and the utmost try worth. The Safe Storage Element generates the salt worth utilizing its random quantity generator. It then derives a passcode verifier worth and a lockbox entropy worth from the offered passcode entropy, the Safe Storage Element’s distinctive cryptographic key, and the salt worth. The Safe Storage Element initializes the counter lockbox with a rely of 0, the offered most try worth, the derived passcode verifier worth, and the salt worth. The Safe Storage Element then returns the generated lockbox entropy worth to the Safe Enclave.

To retrieve the lockbox entropy worth from a counter lockbox later, the Safe Enclave sends the Safe Storage Element the passcode entropy. The Safe Storage Element first increments the counter for the lockbox. If the incremented counter exceeds the utmost try worth, the Safe Storage Element utterly erases the counter lockbox. If the utmost try rely hasn’t been reached, the Safe Storage Element makes an attempt to derive the passcode verifier worth and lockbox entropy worth with the identical algorithm used to create the counter lockbox. If the derived passcode verifier worth matches the saved passcode verifier worth, the Safe Storage Element returns the lockbox entropy worth to the Safe Enclave and resets the counter to 0.

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The keys used to entry password-protected knowledge are rooted within the entropy saved in counter lockboxes. For extra info, see Information Safety overview.

The safe nonvolatile storage is used for all anti-replay providers within the Safe Enclave. Anti-replay providers on the Safe Enclave are used for revocation of knowledge over occasions that mark anti-replay boundaries together with, however not restricted to, the next:

  • Passcode change

  • Enabling or disabling Contact ID or Face ID

  • Including or eradicating a Contact ID fingerprint or Face ID face

  • Contact ID or Face ID reset

  • Including or eradicating an Apple Pay card

  • Erase All Content material and Settings

On architectures that don’t characteristic a Safe Storage Element, EEPROM (electrically erasable programmable read-only reminiscence) is utilized to offer safe storage providers for the Safe Enclave. Identical to the Safe Storage Elements, the EEPROM is hooked up and accessible solely from the Safe Enclave, but it surely doesn’t comprise devoted {hardware} safety features nor does it assure unique entry to entropy (other than its bodily attachment traits) nor counter lockbox performance.

Safe Neural Engine

On gadgets with Face ID, the Safe Neural Engine converts 2D photographs and depth maps right into a mathematical illustration of a person’s face.

On A11 by way of A13 SoCs, the Safe Neural Engine is built-in into the Safe Enclave. The Safe Neural Engine makes use of direct reminiscence entry (DMA) for prime efficiency. An input-output reminiscence administration unit (IOMMU) beneath the sepOS kernel’s management limits this direct entry to approved reminiscence areas.

Beginning with A14 and the M1, the Safe Neural Engine is applied as a safe mode within the Utility Processor’s Neural Engine. A devoted {hardware} safety controller switches between Utility Processor and Safe Enclave duties, resetting Neural Engine state on every transition to maintain Face ID knowledge safe. A devoted engine applies reminiscence encryption, authentication, and entry management. On the identical time, it makes use of a separate cryptographic key and reminiscence vary to restrict the Safe Neural Engine to approved reminiscence areas.

Energy and clock screens

All electronics are designed to function inside a restricted voltage and frequency envelope. When operated outdoors this envelope, the electronics can malfunction after which safety controls could also be bypassed. To assist make sure that the voltage and frequency keep in a protected vary, the Safe Enclave is designed with monitoring circuits. These monitoring circuits are designed to have a a lot bigger working envelope than the remainder of the Safe Enclave. If the screens detect an unlawful working level, the clocks within the Safe Enclave routinely cease and don’t restart till the following SoC reset.

Safe Enclave characteristic abstract

Be aware: A12, A13, S4, and S5 merchandise first launched in Fall 2020 have a 2nd-generation Safe Storage Element; whereas earlier merchandise based mostly on these SoCs have 1st-generation Safe Storage Element.

SoC

Reminiscence Safety Engine

Safe Storage

AES Engine

PKA

A8

Encryption and authentication

EEPROM

Sure

No

A9

Encryption and authentication

EEPROM

DPA safety

Sure

A10

Encryption and authentication

EEPROM

DPA safety and lockable seed bits

OS-bound keys

A11

Encryption, authentication, and replay prevention

EEPROM

DPA safety and lockable seed bits

OS-bound keys

A12 (Apple gadgets launched earlier than Fall 2020)

Encryption, authentication, and replay prevention

Safe Storage Element gen 1

DPA safety and lockable seed bits

OS-bound keys

A12 (Apple gadgets launched after Fall 2020)

Encryption, authentication, and replay prevention

Safe Storage Element gen 2

DPA safety and lockable seed bits

OS-bound keys

A13 (Apple gadgets launched earlier than Fall 2020)

Encryption, authentication, and replay prevention

Safe Storage Element gen 1

DPA safety and lockable seed bits

OS-bound keys and Boot Monitor

A13 (Apple gadgets launched after Fall 2020)

Encryption, authentication, and replay prevention

Safe Storage Element gen 2

DPA safety and lockable seed bits

OS-bound keys and Boot Monitor

A14

Encryption, authentication, and replay prevention

Safe Storage Element gen 2

DPA safety and lockable seed bits

OS-bound keys and Boot Monitor

S3

Encryption and authentication

EEPROM

DPA safety and lockable seed bits

Sure

S4

Encryption, authentication, and replay prevention

Safe Storage Element gen 1

DPA safety and lockable seed bits

OS-bound keys

S5 (Apple gadgets launched earlier than Fall 2020)

Encryption, authentication, and replay prevention

Safe Storage Element gen 1

DPA safety and lockable seed bits

OS-bound keys

S5 (Apple gadgets launched after Fall 2020)

Encryption, authentication, and replay prevention

Safe Storage Element gen 2

DPA safety and lockable seed bits

OS-bound keys

S6

Encryption, authentication, and replay prevention

Safe Storage Element gen 2

DPA safety and lockable seed bits

OS-bound keys

T2

Encryption and authentication

EEPROM

DPA safety and lockable seed bits

OS-bound keys

M1

Encryption, authentication, and replay prevention

Safe Storage Element gen 2

DPA safety and lockable seed bits

OS-bound keys and Boot Monitor

Printed Date: Could 17, 2021

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