All devices MUST meet the requirements of section 9.9.1. Devices which launched on an API level earlier than that of this document are exempted from the requirements of sections 9.9.2 and 9.9.3; instead they MUST meet the requirements in section 9.9 of the Android Compatibility Definition document corresponding to the API level on which the device launched.
Device implementations:
[C-0-1] MUST implement the Direct Boot mode APIs even if they do not support Storage Encryption.
[C-0-2] The [`ACTION_LOCKED_BOOT_COMPLETED`](
https://developer.android.com/reference/android/content/Intent.html#ACTION_LOCKED_BOOT_COMPLETED) and ACTION_USER_UNLOCKED Intents MUST still be broadcast to signal Direct Boot aware applications that Device Encrypted (DE) and Credential Encrypted (CE) storage locations are available for user.
Device implementations:
/data partition), as well as the application shared storage partition (/sdcard partition) if it is a permanent, non-removable part of the device.Encrypted devices:
[C-1-1] MUST boot up without challenging the user for credentials and allow Direct Boot aware apps to access to the Device Encrypted (DE) storage after the ACTION_LOCKED_BOOT_COMPLETED message is broadcasted.
[C-1-2] MUST only allow access to Credential Encrypted (CE) storage after the user has unlocked the device by supplying their credentials (eg. passcode, pin, pattern or fingerprint) and the ACTION_USER_UNLOCKED message is broadcasted.
[C-1-3] MUST NOT offer any method to unlock the CE protected storage without either the user-supplied credentials or a registered escrow key.
[C-1-4] MUST use Verified Boot and ensure that DE keys are cryptographically bound to the device's hardware root of trust.
[C-1-5] MUST encrypt file contents using AES-256-XTS or Adiantum. AES-256-XTS refers to the Advanced Encryption Standard with a 256-bit cipher key length, operated in XTS mode; the full length of the key is 512 bits. Adiantum refers to Adiantum-XChaCha12-AES, as specified at https://github.com/google/adiantum.
[C-1-6] MUST encrypt file names using AES-256-CBC-CTS or Adiantum.
[C-1-12] MUST use AES-256-XTS for file contents and AES-256-CBC-CTS for file names (instead of Adiantum) if the device has Advanced Encryption Standard (AES) instructions. AES instructions are ARMv8 Cryptography Extensions on ARM-based devices, or AES-NI on x86-based devices. If the device does not have AES instructions, the device MAY use Adiantum.
The keys protecting CE and DE storage areas:
[C-1-7] MUST be cryptographically bound to a hardware-backed Keystore.
[C-1-8] CE keys MUST be bound to a user's lock screen credentials.
[C-1-9] CE keys MUST be bound to a default passcode when the user has not specified lock screen credentials.
[C-1-10] MUST be unique and distinct, in other words no user‘s CE or DE key matches any other user’s CE or DE keys.
[C-1-11] MUST use the mandatorily supported ciphers, key lengths and modes.
[C-SR] Are STRONGLY RECOMMENDED to encrypt file system metadata, such as file sizes, ownership, modes, and Extended attributes (xattrs), with a key cryptographically bound to the device's hardware root of trust.
SHOULD make preinstalled essential apps (e.g. Alarm, Phone, Messenger) Direct Boot aware.
The upstream Android Open Source project provides a preferred implementation of this feature based on the Linux kernel “fscrypt” encryption feature.