Hardware security overview
For software to be secure, it must rest on hardware that has security built in. That’s why Apple devices—running iOS, iPadOS, macOS, watchOS, or tvOS—have security capabilities designed into silicon. These capabilities include a CPU that powers system security features, as well as additional silicon that’s dedicated to security functions. Security-focused hardware follows the principle of supporting limited and discretely defined functions in order to minimize attack surface. Such components include a boot ROM, which forms a hardware root of trust for secure boot, dedicated AES engines for efficient and secure encryption and decryption, and a Secure Enclave. The Secure Enclave is a system on chip (SoC) that is included on all recent iPhone, iPad, Apple Watch, Apple TV and HomePod devices, and on a Mac with Apple silicon as well as those with the Apple T2 Security Chip. The Secure Enclave itself follows the same principle of design as the SoC does, containing its own discrete boot ROM and AES engine. The Secure Enclave also provides the foundation for the secure generation and storage of the keys necessary for encrypting data at rest, and it protects and evaluates the biometric data for Face ID and Touch ID.
Storage encryption must be fast and efficient. At the same time, it can’t expose the data (or keying material) it uses to establish cryptographic keying relationships. The AES hardware engine solves this problem by performing fast in-line encryption and decryption as files are written or read. A special channel from the Secure Enclave provides necessary keying material to the AES engine without exposing this information to the Application Processor (or CPU) or overall operating system. This helps ensure that the Apple Data Protection and FileVault technologies protect users’ files without exposing long-lived encryption keys.
Apple has designed secure boot to protect the lowest levels of software against tampering and to allow only trusted operating system software from Apple to load at startup. Secure boot begins in immutable code called the Boot ROM, which is laid down during Apple SoC fabrication and is known as the hardware root of trust. On Mac computers with a T2 chip, trust for macOS secure boot begins with the T2. (Both the T2 chip and the Secure Enclave also execute their own secure boot processes using their own separate boot ROM—this is an exact analogue to how the A-series and M1 family of chips boot securely.)
The Secure Enclave also processes face and fingerprint data from Face ID and Touch ID sensors in Apple devices. This provides secure authentication while keeping user biometric data private and secure. It also allows users to benefit from the security of longer and more complex passcodes and passwords with, in many situations, the convenience of swift authentication for access or purchases.