CDD: Add per-user block-level encryption to storage encryption
Add an alternative section to define encryption requirements for
device implementations using per-user block-level encrypted
partition.
Bug: 184198954
Test: none
Change-Id: Icba5a5541c367f8863466b453e249800c1f6d9aa
(cherry picked from commit 2ea5b7f402881b48dcd02acbc12d1fc2348adb18)
diff --git a/9_security-model/9_9_full-disk-encryption.md b/9_security-model/9_9_full-disk-encryption.md
index cbf4de5..0d89202 100644
--- a/9_security-model/9_9_full-disk-encryption.md
+++ b/9_security-model/9_9_full-disk-encryption.md
@@ -31,9 +31,13 @@
* [C-0-2] MUST enable the data storage encryption by default at the time
the user has completed the out-of-box setup experience.
* [C-0-3] MUST meet the above data storage encryption
-requirement via implementing [File Based Encryption](
-https://source.android.com/security/encryption/file-based.html) (FBE) and
-[Metadata Encryption](https://source.android.com/security/encryption/metadata).
+requirement by implementing one of the following two encryption methods:
+
+ * [File Based Encryption](https://source.android.com/security/encryption/file-based.html)
+ (FBE) and
+ [Metadata Encryption](https://source.android.com/security/encryption/metadata)
+ as described in section 9.9.3.1.
+ * Per-User Block-Level Encryption as described in section 9.9.3.2.
### 9.9.3\. Encryption Methods
@@ -51,6 +55,12 @@
resume on reboot implementation meeting the requirements in
[section 9.9.4](#9_9_4_resume_on_reboot).
* [C-1-4] MUST use Verified Boot.
+
+### 9.9.3.1\. File Based Encryption with Metadata Encryption
+
+If device implementations use File Based Encryption with Metadata Encryption,
+they:
+
* [C-1-5] MUST encrypt file contents and filesystem metadata 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
@@ -94,6 +104,29 @@
File Based Encryption based on the Linux kernel "fscrypt" encryption feature,
and of Metadata Encryption based on the Linux kernel "dm-default-key" feature.
+### 9.9.3.2\. Per-User Block-Level Encryption
+
+If device implementations use per-user block-level encryption, they:
+
+* [C-1-1] MUST enable multi-user support as described in section 9.5.
+* [C-1-2] MUST provide per-user partitions, either using raw partitions or
+logical volumes.
+* [C-1-3] MUST use unique and distinct encryption keys per-user for
+encryption of the underlying block devices.
+* [C-1-4] MUST use AES-256-XTS for block-level encryption of the user
+partitions.
+
+* The keys protecting the per-user block-level encrypted devices:
+
+ * [C-1-5] MUST be cryptographically bound to a hardware-backed Keystore.
+ This keystore MUST be bound to Verified Boot and the device's hardware
+ root of trust.
+ * [C-1-6] MUST be bound to the corresponding user's lock screen
+ credentials.
+
+Per-user block-level encryption can be implemented using the Linux kernel
+“dm-crypt” feature over per-user partitions.
+
### 9.9.4\. Resume on Reboot
Resume on Reboot allows unlocking the CE storage of all apps, including those
