docs: Expanded description of "Key Attestation" N Preview feature.

      value: TV 录制

    - name: zh-tw-lang

      value: 電視錄製

  - title: Key Attestation

    path: /preview/features/key-attestation.html

  - title: Network Security Configuration

    path: /preview/features/security-config.html

    path_attributes:

For more information, see <a href="{@docRoot}preview/features/direct-boot.html">Direct Boot</a>.</p>

</p>

<h2 id="key_attestation">Key Attestation</h2>

<p>Hardware-backed keystores provide a much safer method to create, store,

and use cryptographic keys on Android devices. They protect keys from the

Linux kernel, potential Android vulnerabilities, and extraction

from rooted devices.</p>

<p>To make it easier and more secure to use hardware-backed keystores,

Android N introduces Key Attestation. Apps and off-devices can use Key

Attestation to strongly determine whether an RSA or EC key pair is

hardware-backed, what the properties of the key pair are, and what

  constraints are applied to its usage and validity. </p>

<p>Apps and off-device services can request information about a key pair

through an X.509 attestation certificate which must be signed by a valid

attestation key. The attestation key is an ECDSA signing key which is

injected into the device’s hardware-backed keystore at the factory.

Therefore, an attestation certificate signed by a valid attestation

key confirms the existence of a hardware-backed keystore, along with

  details of key pairs in that keystore.</p>

<p>To ensure that the device is using a secure, official Android factory

image, Key Attestation requires that the device <a

class="external-link"

href="https://source.android.com/security/verifiedboot/verified-boot.html#bootloader_requirements">bootloader</a>

provide the following information to the <a class="external-link"

href="https://source.android.com/security/trusty/index.html">Trusted

Execution Environment (TEE)</a>:</p>

<ul>

<li>The OS version and patch level installed on the device</li>

<li>The <a href="https://source.android.com/security/verifiedboot/index.html"

class="external-link" >Verified Boot</a> public key and lock status</li>

  </ul>

<p>

  Android N introduces <em>key attestation</em>, a new security tool that helps

  you make sure that the key pairs stored within a device's <a class=

  "external-link" href=

  "https://source.android.com/security/keystore/"><em>hardware-backed

  keystore</em></a> properly protect the sensitive information that your app

  uses. By using this tool, you gain additional confidence that your app

  interacts with keys that reside in secure hardware, even if the device

  running your app is rooted. If you use keys from the hardware-backed keystore

  in your apps, you should use this tool, particularly if you use the keys to

  verify sensitive information within your app.

</p>

<p>For more information about the hardware-backed keystore feature,

see the guide for <a href="https://source.android.com/security/keystore/"

class="external-link">Hardware-backed Keystore</a>.</p>

<p>

  Key attestation allows you to verify that an RSA or EC key pair has been

  created and stored in a device’s hardware-backed keystore within the device’s

  trusted execution environment (TEE). The tool also allows you to use an

  off-device service, such as your app's back-end server, to determine and

  strongly verify the uses and validity of the key pair. These features provide

  an additional level of security that protects the key pair, even if someone

  roots the device or compromises the security of the Android platform running

  on the device.

</p>

<p>In addition to Key Attestation, Android N also introduces

  fingerprint-bound keys that are not revoked on fingerprint enrollment.</p>

<p>

  For more information, see the

  <a href="{@docRoot}preview/features/key-attestation.html">Key Attestation</a>

  developer documentation.

</p>

<h2 id="network_security_config">Network Security Config</h2>