Trusted Boot

Trusted Boot is a Knox Platform feature that identifies and distinguishes authorized from unauthorized boot loaders, segregating out-of-date boot loaders before they can compromise your mobile devices.

Enterprises can check device integrity on demand through Knox Device Health Attestation, which reads Trusted Boot collected measurement data, along with an Security Enhancement (SE) for Android enforcement setting, to form the basis of a device health verdict.

Secure lockdown on tampering

Bootloader measurements are recorded in secure TrustZone memory during device boot. At runtime, apps operating in the secure TrustZone can use these measurements to make security-critical decisions, such as whether or not to:

• Release cryptographic keys from the Knox Keystore.
• Launch the Work profile app container.

The key derivation mechanism for the device’s work profile contains a tamper fuse. If an unauthorized or out-of-date component version is detected, the fuse is set. Once the tamper fuse is set, sensitive work apps and data within the Work container are permanently encrypted and inaccessible as the integrity of the device is no longer guaranteed or validated. In addition, the encryption key will not be derivable.

The device user can still boot the device and launch personal apps. This flexibility promotes a nice balance between consumer functions, such as smartphone calls and personal apps, and the requirement to protect enterprise data.

Building on Secure Boot

Before adopting Trusted Boot to work along with Secure Boot, Samsung devices used Secure Boot to prevent unauthorized bootloaders and operating systems from loading during start-up.

Secure Boot is implemented by each bootloader cryptographically verifying the signature of the next bootloader in sequence, using a certificate chain with its root-of-trust resident in hardware. If verification fails at any step, the boot process terminates.

While Secure Boot is effective at preventing unauthorized bootloaders, it is unable to distinguish between different authorized binary versions. For example, Secure Boot can’t distinguish between a bootloader with a known vulnerability as opposed to a later patched version, since both versions have valid signatures.

Trusted Boot was introduced to verify all the software components in the boot chain (bootloader, kernel, and platform build) intended to be deployed together.

Knox Verified Boot (KVB)

Knox Verified Boot (KVB) implements the Trusted Boot process on Knox devices. KVB both extends and enhances Android Verified Boot (AVB); while AVB only checks the integrity of the kernel and platform components, KVB extends checks to also validate earlier bootloaders.

This provides a more comprehensive guarantee the device is booting using properly signed components from the same build.