docs/html/training/safetynet/index.jd

page.title=Checking Device Compatibility with SafetyNet

@jd:body


<div id="tb-wrapper">
<div id="tb">

  <h2>In this document</h2>
  <ol>
  <li><a href="#tos">Additional Terms of Service</a></li>
  <li><a href="#connect-play">Connect to Play Services</a></li>
  <li><a href="#cts-check">Requesting a Compatibility Check</a>
    <ol>
      <li><a href="#single-use-token">Obtain Single Use Token</a></li>
      <li><a href="#compat-check-request">Send Compatibility Check Request</a></li>
      <li><a href="#compat-check-response">Read Compatibility Check Response</a></li>
      <li><a href="#verify-compat-check">Verify Compatibility Check Response</a></li>
    </ol>
  </li>
  </ol>

</div>
</div>

<p>
  SafetyNet provides services for analyzing the configuration of a particular device, to make sure
  that apps function properly on a particular device and that users have a great experience.
</p>

<p>
  The service provides an API your app can use to analyze the device where it is installed. The API
  uses software and hardware information on the device where your app is installed to create a
  profile of that device. The service then attempts to match it to a list of device models that
  have passed Android compatibility testing. This check can help you decide if the device is
  configured in a way that is consistent with the Android platform specifications and has the
  capabilities to run your app.
</p>

<p>
  This document shows you how to use SafetyNet for analyzing a device and help you determine if
  your app will function as expected on that device.
</p>

<h2 id="tos">
  Additional Terms of Service
</h2>

<p>
  By accessing or using the SafetyNet APIs, you agree to the <a href=
  "https://developers.google.com/terms/">Google APIs Terms of Service</a>, and to these Additional
  Terms. Please read and understand all applicable terms and policies before accessing the APIs.
</p>

<div class="sdk-terms" onfocus="this.blur()" style="width:678px">
<h3 class="norule">SafetyNet Terms of Service</h3>
As with any data collected in large volume from in-the-field observation, there is a chance of
both false positives and false negatives. We are presenting the data to the best of our
understanding. We extensively test our detection mechanisms to ensure accuracy, and we are
committed to improving those methods over time to ensure they continue to remain accurate.

You agree to comply with all applicable law, regulation, and third party rights (including
without limitation laws regarding the import or export of data or software, privacy, and local
laws). You will not use the APIs to encourage or promote illegal activity or violation of third
party rights. You will not violate any other terms of service with Google (or its affiliates).

You acknowledge and understand that the SafetyNet API works by collecting hardware and software
information, such as device and application data and the results of integrity checks, and sending
that data to Google for analysis. Pursuant to Section 3(d) of the
<a href= "https://developers.google.com/terms/">Google APIs Terms of Service</a>, you agree that if
you use the APIs that it is your responsibility to provide any necessary notices or consents for the
collection and sharing of this data with Google.
</div>

<h2 id="connect-play">
  Connect to Google Play Services
</h2>

<p>
  The SafetyNet API is part of Google Play services. To connect to the API, you need to create an
  instance of the Google Play services API client. For details about using the client in your app,
  see <a href="{@docRoot}google/auth/api-client.html#Starting">Accessing Google
  APIs</a>. Once you have established a connection to Google Play services, you can use the Google
  API client classes to connect to the SafetyNet API.
</p>

<p>
  To connect to the API, in your activity's <a href=
  "{@docRoot}reference/android/app/Activity.html#onCreate(android.os.Bundle)">onCreate()</a>
  method, create an instance of Google API Client using <a href=
  "{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.Builder.html">
  {@code GoogleApiClient.Builder}</a>. Use the builder to add the SafetyNet API, as shown in the
  following code example:
</p>

<pre>
protected synchronized void buildGoogleApiClient() {
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .addApi(SafetyNet.API)
            .addConnectionCallbacks(myMainActivity.this)
            .build();
}
</pre>

<p class="note">
  <strong>Note:</strong> You can only call these methods after your app has established a connection to
  Google Play services by receiving the <a href=
  "{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.ConnectionCallbacks.html#onConnected(android.os.Bundle)">
  {@code onConnected()}</a> callback. For details about listening for a completed client connection,
  see <a href="{@docRoot}google/auth/api-client.html#Starting">Accessing Google APIs</a>.
</p>

<h2 id="cts-check">
  Requesting a Compatibility Check
</h2>

<p>
  A SafetyNet compatibility check allows your app to check if the device where it is running
  matches the profile of a device that has passed Android compatibility testing. The compatibility
  check creates a device profile by gathering information about the device hardware and software
  characteristics, including the platform build.
</p>

<p>
  Using the API to perform a check requires a few implementation steps in your app. Once you have
  established a connection to Google Play services and requested the SafetyNet API from the Google
  API client, your app can then perform the following steps to use the service:
</p>

<ul>
  <li>Obtain a single use token
  </li>

  <li>Send the compatibility check request
  </li>

  <li>Read the response
  </li>

  <li>Validate the response
  </li>
</ul>

<p>
  For more information about Android compatibility testing, see <a href=
  "https://source.android.com/compatibility/index.html" class="external-link">
  Android Compatibility</a> and the <a href=
  "https://source.android.com/compatibility/cts-intro.html" class="external-link">
  Compatibility Testing Suite</a> (CTS).
</p>

<p>
  SafetyNet checks use network resources, and so the speed of responses to requests can vary,
  depending on a device's network connection status. The code described in this section should be
  executed outside of your app's main execution thread, to avoid pauses and unresponsiveness in
  your app user interface. For more information about using separate execution threads, see
  <a href="{@docRoot}training/multiple-threads/index.html">Sending Operations
  to Multiple Threads</a>.
</p>

<h3 id="single-use-token">
  Obtain a single use token
</h3>

<p>
  The SafetyNet API uses security techniques to help you verify the integrity of the communications
  between your app and the service. When you request a compatibility check, you must provide a
  single use token in the form of a number used once, or <em>nonce</em>, as part of your request. A
  nonce is a random token generated in a cryptographically secure manner.
</p>

<p>
  You can obtain a nonce by generating one within your app each time you make a compatibility check
  request. As a more secure option, you can obtain a nonce from your own server, using a secure
  connection.
</p>

<p>
  A nonce used with a SafetyNet request should be at least 16 bytes in length. After you make a
  check request, the response from the SafetyNet service includes your nonce, so you can verify it
  against the one you sent. As the name indicates, you should only use a nonce value once, for a
  single check request. Use a different nonce for any subsequent check requests. For tips on using
  cryptography functions, see <a href=
  "{@docRoot}training/articles/security-tips.html#Crypto">Security Tips</a>.
</p>

<h3 id="compat-check-request">
  Send the compatibility check request
</h3>

<p>
  After you have established a connection to Google Play services and created a nonce, you are
  ready to make a compatibility check request. Since the response to your request may not be
  immediate, you set up a callback listener to catch the response from the service, as shown in the
  following code example:
</p>

<pre>
byte[] nonce = getRequestNonce(); // Should be at least 16 bytes in length.
SafetyNet.SafetyNetApi.attest(mGoogleApiClient, nonce)
        .setResultCallback(new ResultCallback&lt;SafetyNetApi.AttestationResult&gt;() {

    &#64;Override
    public void onResult(SafetyNetApi.AttestationResult result) {
        Status status = result.getStatus();
        if (status.isSuccess()) {
            // Indicates communication with the service was successful.
            // result.getJwsResult() contains the result data
        } else {
            // An error occurred while communicating with the service
        }
    }
});
</pre>

<p>
  The <a href=
  "{@docRoot}reference/com/google/android/gms/common/api/Status.html#isSuccess()">
  {@code isSuccess()}</a>
  method indicates whether or not communication with the service was successful, but does not
  indicate if the device has passed the compatibility check. The next section discusses how to read
  the check result and verify its integrity.
</p>

<h3 id="compat-check-response">
  Read the compatibility check response
</h3>

<p>
  When your app communicates with SafetyNet, the service provides a response containing the result
  and additional information to help you verify the integrity of the message. The result is
  provided as a <a href=
  "{@docRoot}reference/com/google/android/gms/safetynet/SafetyNetApi.html">
  {@code AttestationResult}</a>
  object. Use the <a href=
  "{@docRoot}reference/com/google/android/gms/safetynet/SafetyNetApi.AttestationResult.html#getJwsResult()">
{@code getJwsResult()}</a> method of this object to obtain the data of the request. The response is
  formatted as a <a href="https://tools.ietf.org/html/draft-ietf-jose-json-web-signature-36" class="external-link">
  JSON Web Signature</a> (JWS), the following JWS excerpt shows the format of the payload data:
</p>

<pre>
{
"nonce": "R2Rra24fVm5xa2Mg",
"timestampMs": 9860437986543,
"apkPackageName": "com.package.name.of.requesting.app",
"apkCertificateDigestSha256": ["base64 encoded, SHA-256 hash of the
certificate used to sign requesting app"],
"apkDigestSha256": "base64 encoded, SHA-256 hash of the app's APK",
"ctsProfileMatch": true,
}
</pre>

<p>
  If the value of {@code ctsProfileMatch} is {@code true}, this indicates that the device
  profile matches a device that has passed Android compatibility testing. If the output of the
  <a href=
  "{@docRoot}reference/com/google/android/gms/safetynet/SafetyNetApi.AttestationResult.html#getJwsResult()">
{@code getJwsResult()}</a> method is null or contains an {@code error:} field, then communication
  with the service failed and should be retried. You should use an <a class="external-link" href=
  "https://developers.google.com/api-client-library/java/google-http-java-client/backoff">
  exponential backoff</a> technique for retries, to avoid flooding the service with additional requests.
</p>

<h3 id="verify-compat-check">
  Verify the compatibility check response
</h3>

<p>
  You should take steps to make sure the response received by your app actually came from the
  SafetyNet service and matches the request data you provided. Follow these steps to verify the
  origin of the JWS message:
</p>

<ul>
  <li>Extract the SSL certificate chain from the JWS message.
  </li>

  <li>Validate the SSL certificate chain and use SSL hostname matching to verify that the leaf
  certificate was issued to the hostname {@code attest.android.com}.
  </li>

  <li>Use the certificate to verify the signature of the JWS message.
  </li>
</ul>

<p>
  After completing this validation, you should also check the data of the JWS message to make sure
  it matches your original request, including the nonce, timestamp, package name, and the SHA-256
  hashes. You can perform these validation steps within your app, or as a more secure option, send
  the entire JWS response to your own server for verification, via a secure connection.
</p>

<h4>
  Validating the response with Google APIs
</h4>

<p>
  Google provides an Android Device Verification API for validating the output of the SafetyNet
  compatibility check. This API performs a validation check on the JWS message returned from the
  SafetyNet service.
</p>

<p>
  To enable access to the Android Device Verification API:
</p>

<ol>
  <li>Go to the <a href="https://console.developers.google.com/" class="external-link">
    Google Developers Console</a>.
  </li>

  <li>Select a project, or create a new one.
  </li>

  <li>In the sidebar on the left, expand <strong>APIs &amp; auth</strong>.
    Next, click <strong>APIs</strong>. In the
  list of APIs, make sure all of the APIs you are using show a status of <strong>ON</strong>.
  </li>

  <li>In the <strong>Browse APIs</strong> list, find the
    <strong>Android Device Verification API</strong> and turn it
  on.
  </li>

  <li>Obtain your API key by expanding <strong>APIs &amp; auth</strong> and
    clicking <strong>Credentials</strong>.
  Record the <strong>API KEY</strong> value on this page for later use.
  </li>
</ol>

<p>
  After enabling this API for your project, you can call the verification service from your app or
  server. You need the contents of the JWS message from the SafetyNet API and your API key to call
  the verification API and get a result.
</p>

<p>
  To use the Android Device Verification API:
</p>

<ol>
  <li>Create a JSON message containing the entire contents of the JWS message in the following
  format:
<pre>
{ "signedAttestation": "&lt;output of getJwsResult()&gt;" }
</pre>
  </li>

  <li>Use an HTTP POST request to send the message with a Content-Type of {@code "application/json"}
  to the following URL:
<pre>
https&#58;&#47;&#47;www.googleapis.com/androidcheck/v1/attestations/verify?key=&lt;your API key&gt;
</pre>
  </li>

  <li>The service validates the integrity of the message, and if the message is valid, it returns a
  JSON message with the following contents:

<pre>
{ “isValidSignature”: true }
</pre>
  </li>
</ol>

<p class="note">
  <strong>Important:</strong> This use of the Android Device Verification API only validates that the
  provided JWS message was received from the SafetyNet service. It <em>does not</em> verify that the
  payload data matches your original compatibility check request.
</p>