Merge "docs: Adding N preview docs on Direct Boot feature" into mnc-mr-docs

page.title=Direct Boot

page.keywords=preview,sdk,direct boot

page.tags=androidn

@jd:body

<div id="tb-wrapper">

<div id="tb">

  <h2>In this document</h2>

  <ol>

    <li><a href="#run">Requesting Access to Run During Direct Boot</a></li>

    <li><a href="#access">Accessing Device Encrypted Storage</a></li>

    <li><a href="#notification">Getting Notified of User Unlock</a></li>

    <li><a href="#migrating">Migrating Existing Data</a></li>

    <li><a href="#testing">Testing Your Encryption Aware App</a></li>

  </ol>

</div>

</div>

<p>The system now runs in a secure, Direct Boot mode when the device has been

powered on but the user has not unlocked the device. To support this, the

system provides two storage locations for data:</p>

<ul>

<li><i>Credential encrypted storage</i>, which is the default storage location

and available only after the user has unlocked the device.</li>

<li><i>Device encrypted storage</i>, which is a storage location available both

during Direct Boot mode and after the user has unlocked the device.</li>

</ul>

<p>By default apps will not run during Direct Boot mode, because apps won't

have access to credential encrypted storage.</p>

<p>If your app needs to take action during Direct Boot mode, you can register

app components that should be run during this mode. Some common use cases

for applications needing to run during Direct Boot mode include:</p>

<ul>

<li>Applications that have scheduled notifications, such as alarm clock

apps.</li>

<li>Applications that provide important user notifications, like SMS apps.</li>

<li>Applications providing accessibility services, like Talkback.</li>

</ul>

<p>If your app needs to access data while running in Direct Boot mode, use

device encrypted storage. Device encrypted storage contains data

encrypted with a key that is only available after a device has performed a

successful verified boot.</p>

<p>For data that should be encrypted with a key associated with user

credentials, such as a PIN or password, use credential encrypted storage.

Credential encrypted storage is only available after the user has successfully

unlocked the device, up until when the user restarts the device again. If the

user enables the lock screen after unlocking the device, this will not lock

credential encrypted storage.</p>

<h2 id="run">Requesting Access to Run During Direct Boot</h2>

<p>Applications must register their components with the system before they

can run during the limited Direct Boot mode, or access device encrypted

storage. Applications register with the system by marking components as

<i>encryption aware</i>. To mark your component as encryption aware, set the

<code>android:encryptionAware</code> attribute to true in your manifest.<p>

<p>When a component is marked as encryption aware, the component receives a

new <code>LOCKED_BOOT_COMPLETED</code> broadcast message from the

system when the device has been restarted. At this point device encrypted

storage is available, and your component can run whatever tasks need to be

done during Direct Boot mode, such as triggering a scheduled alarm.</p>

<p>The following code snippet is an example of how to register a

<code>BroadcastReceiver</code> as encryption aware, and add an intent filter

for <code>LOCKED_BOOT_COMPLETED</code>, in the application manifest:</p>

<pre>

<receiever

  android:encryptionAware="true" >

  ...

  <intent-filter>

    <action android:name="android.intent.action.LOCKED_BOOT_COMPLETED" />

  </intent-filter>

</receiver>

</pre>

<p>Once the user has unlocked the device, components can access both the

device encrypted storage as well as credential encrypted storage.</p>

<h2 id="access">Accessing Device Encrypted Storage</h2>

<p>To access device encrypted storage, create a second <code>Context</code>

instance by calling <code>Context.createDeviceEncryptedStorageContext()</code>.

All storage API calls made using this context access the device encrypted

storage. The following example accesses the device encrypted storage and opens

an existing app data file:</p>

<pre>

Context directBootContext = Context.createDeviceEncryptedStorageContext();

// Access appDataFilename that lives in device encrypted storage

FileInputStream inStream = directBootContext.openFileInput(appDataFilename);

// Use inStream to read content...

</pre>

<p class="note"><strong>Note:</strong> Use device encrypted storage only for

information that must be accessible during the Direct Boot mode.

Don't use device encrypted storage as a general-purpose encrypted store.

For private user information, or encrypted data that isn't needed during

Direct Boot mode, use credential encrypted storage.</p>

<h2 id="notification">Getting Notified of User Unlock</h2>

<p>Once the user unlocks the device after restart, your app can switch to

accessing credential encrypted storage and use regular system services that

depend on user credentials, like Google Play Services.</p>

<p>To get notified when the user unlocks the device after a reboot,

register a <code>BroadcastReceiver</code> from a running component to listen

for the <code>ACTION_USER_UNLOCKED</code> message. Or, you can receive the

existing <code>BOOT_COMPLETED</code> message, which now indicates the

device has booted and the user has unlocked the device.</p>

<p>You can directly query if the user has unlocked the device by calling

<code>UserManager.isUserUnlocked()</code>.</p>

<h2 id="migrating">Migrating Existing Data</h2>

<p>If a user updates their device to use Direct Boot mode, you might have

existing data that needs to get migrated to device encrypted storage. Use

<code>Context.migrateSharedPreferencesFrom()</code> and

<code>Context.migrateDatabaseFrom()</code> to migrate preference and database

data between credential encrypted storage and device encrypted storage.</p>

<p>Use your best judgment when deciding what data to migrate from credential

encrypted storage to device encrypted storage. You should not be migrating

private user information, such as passwords or authorization tokens, to

device encrypted storage. In some scenarios, you might need to manage

separate sets of data in the two encrypted stores.</p>

<h2 id="testing">Testing Your Encryption Aware App</h2>

<p>Test your encryption aware application using the new Direct Boot mode.

On supported devices with Android N Developer Preview installed, enable Direct

Boot by doing one of the following:</p>

<ul>

<li>On the device, enable <b>Developer options</b> if you haven't already by

going to <b>Settings &gt; About phone</b>, and tap <b>Build number</b> seven

times. Once developer options is available, go to <b>Settings &gt;

Developer options</b> and select <b>Convert to file encryption</b>.

Note that enabling Direct Boot will wipe user data.</li>

<li>Use the following adb shell commands to wipe user data and enable Direct

Boot mode:

<pre class="no-pretty-print">

$ adb reboot-bootloader

$ fastboot --wipe-and-use-fbe

</pre>

</li>

</ul>

<p>An emulated Direct Boot mode is also available, in case you need to switch

modes on your test devices. Emulated mode should only be used during

development and may cause data loss. To enable emulated Direct Boot mode,

set a lock pattern on the device, choose "No thanks" if prompted for a

secure start-up screen when setting a lock pattern, and then use the

following adb shell command:</p>

<pre class="no-pretty-print">

$ adb shell sm set-emulate-fbe true

</pre>

<p>To turn off emulated Direct Boot mode, use the following command:</p>

<pre class="no-pretty-print">

$ adb shell sm set-emulate-fbe false

</pre>

<p>Note that using these commands will automatically cause the device to

reboot.</p>