android_frameworks_base/docs/html/training/articles/security-config.jd

page.title=Network Security Configuration
page.keywords=security,network,config
page.metaDescription=Feature that allows app developers to customize network security settings in a safe configuration file.
page.image=images/cards/card-nyc_2x.jpg

@jd:body

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

<h2>In this document</h2>
<ol>
  <li><a href="#manifest">Adding a Security Configuration File</a></li>
  <li><a href="#CustomTrust">Customizing Trusted CAs</a>
      <ol>
      <li><a href="#ConfigCustom">Configuring a Trusted Custom CA</a></li>
      <li><a href="#LimitingCas">Limiting the Set of Trusted CAs</a></li>
      <li><a href="#TrustingAdditionalCas">Trusting Additional CAs</a></li>
      </ol>
  </li>
  <li><a href="#TrustingDebugCa">Debugging-only CAs</a></li>
  <li><a href="#CleartextTrafficPermitted">Opting Out of Cleartext Traffic</a></li>
  <li><a href="#CertificatePinning">Pinning Certificates</a></li>
  <li><a href="#ConfigInheritance">Configuration Inheritance Behavior</a></li>
  <li><a href="#FileFormat">Configuration File Format</a></li>
</ol>
</div>
</div>


<p>
  The Network Security Configuration feature lets apps customize their network
  security settings in a safe, declarative configuration file without modifying
  app code. These settings can be configured for specific domains and for a
  specific app. The key capabilities of this feature are as follows:
</p>

<ul>
  <li>
    <b>Custom trust anchors:</b> Customize which Certificate Authorities (CA)
    are trusted for an app's secure connections. For
    example, trusting particular self-signed certificates or restricting the
    set of public CAs that the app trusts.
  </li>

  <li>
    <b>Debug-only overrides:</b> Safely debug secure connections in an app
    without added risk to the installed base.
  </li>

  <li>
    <b>Cleartext traffic opt-out:</b> Protect apps from
    accidental usage of cleartext traffic.
  </li>

  <li>
    <b>Certificate pinning:</b> Restrict an app's secure connection to
    particular certificates.
  </li>
</ul>


<h2 id="manifest">Adding a Security Configuration File</h2>

<p>
  The Network Security Configuration feature uses an XML file where you specify
  the settings for your app. You must include an entry in the manifest of your
  app to point to this file. The following code excerpt from a manifest
  demonstrates how to create this entry:
</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;manifest ... &gt;
    &lt;application android:networkSecurityConfig="@xml/network_security_config"
                    ... &gt;
        ...
    &lt;/application&gt;
&lt;/manifest&gt;
</pre>

<h2 id="CustomTrust">Customizing Trusted CAs</h2>

<p>
  An app may want to trust a custom set of CAs instead of the platform
  default. The most common reasons of this are:
</p>

<ul>
  <li>Connecting to a host with a custom certificate authority, such as a
  CA that is self-signed or is issued internally within a company.
  </li>

  <li>Limiting the set of CAs to only the CAs you trust instead of every
  pre-installed CA.
  </li>

  <li>Trusting additional CAs not included in the system.
  </li>
</ul>

<p>
  By default, secure connections (using protocols like TLS and HTTPS) from all
  apps trust the pre-installed system CAs, and apps targeting Android 6.0 (API
  level 23) and lower also trust the user-added CA store by default. An app can
  customize its own connections using {@code base-config} (for app-wide
  customization) or {@code domain-config} (for per-domain customization).
</p>


<h3 id="ConfigCustom">Configuring a Custom CA</h3>

<p>
  Assume you want to connect to your host which uses a self-signed SSL
  certificate or to a host whose SSL certificate is issued by a non-public CA
  which you trust, such as your company's internal CA.
</p>

<p>
  <code>res/xml/network_security_config.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;domain-config&gt;
        &lt;domain includeSubdomains="true"&gt;example.com&lt;/domain&gt;
        &lt;trust-anchors&gt;
            &lt;certificates src="@raw/my_ca"/&gt;
        &lt;/trust-anchors&gt;
    &lt;/domain-config&gt;
&lt;/network-security-config&gt;
</pre>
</p>

<p>
  Add the self-signed or non-public CA certificate, in PEM or DER format, to
  {@code res/raw/my_ca}.
</p>


<h3 id="LimitingCas">Limiting the Set of Trusted CAs</h3>

<p>
  An app that does not want to trust all CAs trusted by system can
  instead specify its own reduced set of CAs to trust. This protects the
  app from fradulent certificates issued by any of the other CAs.
</p>

<p>
  The configuration to limit the set of trusted CAs is similar to <a href=
  "#ConfigCustom">trusting a custom CA</a> for a specific domain except
  that multiple CAs are provided in the resource.
</p>

<p>
<code>res/xml/network_security_config.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;domain-config&gt;
        &lt;domain includeSubdomains="true"&gt;secure.example.com&lt;/domain&gt;
        &lt;domain includeSubdomains="true"&gt;cdn.example.com&lt;/domain&gt;
        &lt;trust-anchors&gt;
            &lt;certificates src="@raw/trusted_roots"/&gt;
        &lt;/trust-anchors&gt;
    &lt;/domain-config&gt;
&lt;/network-security-config&gt;
</pre>
</p>

<p>
  Add the trusted CAs, in PEM or DER format, to {@code res/raw/trusted_roots}.
  Note that if using PEM format the file must contain <em>only</em> PEM data
  and no extra text. You can also provide multiple
  <a href="#certificates"><code>&lt;certificates&gt;</code></a>
elements instead of one.
</p>


<h3 id="TrustingAdditionalCas">
  Trusting Additional CAs
</h3>

<p>
  An app may want to trust additional CAs not trusted by the system,
  this could be due to the system not yet including the CA or a CA that does
  not meet the requirements for inclusion into the Android system. An
  app can do this by specifying multiple certificate sources for a
  configuration.
</p>
<p>
<code>res/xml/network_security_config.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;base-config&gt;
        &lt;trust-anchors&gt;
            &lt;certificates src="@raw/extracas"/&gt;
            &lt;certificates src="system"/&gt;
        &lt;/trust-anchors&gt;
    &lt;/base-config&gt;
&lt;/network-security-config&gt;
</pre>
</p>


<h2 id="TrustingDebugCa">Configuring CAs for Debugging</h2>

<p>
  When debugging an app that connects over HTTPS, you may want to
  connect to a local development server, which does not have the SSL
  certificate for your production server. In order to support this without any
  modification to your app's code, you can specify debug-only CAs, which
  are trusted <i>only</i> when <a href=
  "{@docRoot}guide/topics/manifest/application-element.html#debug">
android:debuggable</a>
  is {@code true}, by using {@code debug-overrides}. Normally, IDEs and build
  tools set this flag automatically for non-release builds.
</p>

<p>
  This is safer than the usual conditional code because, as a security
  precaution, app stores do not accept apps which are marked
  debuggable.
</p>

<p>
<code>res/xml/network_security_config.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;debug-overrides&gt;
        &lt;trust-anchors&gt;
            &lt;certificates src="@raw/debug_cas"/&gt;
        &lt;/trust-anchors&gt;
    &lt;/debug-overrides&gt;
&lt;/network-security-config&gt;
</pre>
</p>


<h2 id="CleartextTrafficPermitted">Opting Out of Cleartext Traffic</h2>

<p>
  Applications intending to connect to destinations using only secure
  connections can opt-out of supporting cleartext (using the unencrypted HTTP
  protocol instead of HTTPS) to those destinations. This option helps prevent
  accidental regressions in apps due to changes in URLs provided by external
  sources such as backend servers.
  See {@link android.security.NetworkSecurityPolicy#isCleartextTrafficPermitted
  NetworkSecurityPolicy.isCleartextTrafficPermitted()} for more details.
</p>

<p>
  For example, an app may want to ensure that all connections to {@code
  secure.example.com} are always done over HTTPS to protect sensitive traffic
  from hostile networks.
</p>

<p>
<code>res/xml/network_security_config.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;domain-config cleartextTrafficPermitted="false"&gt;
        &lt;domain includeSubdomains="true"&gt;secure.example.com&lt;/domain&gt;
    &lt;/domain-config&gt;
&lt;/network-security-config&gt;
</pre>
</p>


<h2 id="CertificatePinning">Pinning Certificates</h2>

<p>
  Normally, an app trusts all pre-installed CAs. If any of these CAs were to
  issue a fradulent certificate, the app would be at risk from a
  man-in-the-middle attack. Some apps choose to limit the set of certificates
  they accept by either limiting the set of CAs they trust or by certificate
  pinning.
</p>

<p>
  Certificate pinning is done by providing a set of certificates by hash of the
  public key (<code>SubjectPublicKeyInfo</code> of the X.509 certificate). A
  certificate chain is then valid only if the certificate chain contains at
  least one of the pinned public keys.
</p>

<p>
  Note that, when using certificate pinning, you should always include a backup
  key so that if you are forced to switch to new keys or change CAs (when
  pinning to a CA certificate or an intermediate of that CA), your
  app's connectivity is unaffected. Otherwise, you must push out
  an update to the app to restore connectivity.
</p>

<p>
  Additionally, it is possible to set an expiration time for pins after which
  pinning is not performed. This helps prevent connectivity issues in
  apps which have not been updated. However, setting an expiration time
  on pins may enable pinning bypass.
</p>

<p>
<code>res/xml/network_security_config.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;domain-config&gt;
        &lt;domain includeSubdomains="true"&gt;example.com&lt;/domain&gt;
        &lt;pin-set expiration="2018-01-01"&gt;
            &lt;pin digest="SHA-256"&gt;7HIpactkIAq2Y49orFOOQKurWxmmSFZhBCoQYcRhJ3Y=&lt;/pin&gt;
            &lt;!-- backup pin --&gt
            &lt;pin digest="SHA-256"&gt;fwza0LRMXouZHRC8Ei+4PyuldPDcf3UKgO/04cDM1oE=&lt;/pin&gt;
        &lt;/pin-set&gt;
    &lt;/domain-config&gt;
&lt;/network-security-config&gt;
</pre>
</p>


<h2 id="ConfigInheritance">Configuration Inheritance Behavior</h2>

<p>
  Values not set in a specific configuration are inherited. This behavior allows
  more complex configurations while keeping the configuration file readable.
</p>

<p>
  If a value is not set in a specific entry, then the value from the more
  general entry is used. For example, values not set in a {@code domain-config}
  are taken from the parent {@code domain-config}, if nested, or from the {@code
  base-config} if not. Values not set in the {@code base-config} use the
  platform default values.
</p>

<p>
  For example, consider where all connections to subdomains of {@code
  example.com} must use a custom set of CAs. Additonally, cleartext traffic to
  these domains is permitted <em>except</em> when connecting to {@code
  secure.example.com}. By nesting the configuration for {@code
  secure.example.com} inside the configuration for {@code example.com}, the
  {@code trust-anchors} does not need to be duplicated.
</p>

<p>
<code>res/xml/network_security_config.xml</code>:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;domain-config&gt;
        &lt;domain includeSubdomains="true"&gt;example.com&lt;/domain&gt;
        &lt;trust-anchors&gt;
            &lt;certificates src="@raw/my_ca"/&gt;
        &lt;/trust-anchors&gt;
        &lt;domain-config cleartextTrafficPermitted="false"&gt;
            &lt;domain includeSubdomains="true"&gt;secure.example.com&lt;/domain&gt;
        &lt;/domain-config&gt;
    &lt;/domain-config&gt;
&lt;/network-security-config&gt;
</pre>
</p>


<h2 id="FileFormat">Configuration File Format</h2>

<p>
  The Network Security Configuration feature uses an XML file format.
  The overall structure of the file is shown in the following code sample:
</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;network-security-config&gt;
    &lt;base-config&gt;
        &lt;trust-anchors&gt;
            &lt;certificates src="..."/&gt;
            ...
        &lt;/trust-anchors&gt;
    &lt;/base-config&gt;

    &lt;domain-config&gt;
        &lt;domain&gt;android.com&lt;/domain&gt;
        ...
        &lt;trust-anchors&gt;
            &lt;certificates src="..."/&gt;
            ...
        &lt;/trust-anchors&gt;
        &lt;pin-set&gt;
            &lt;pin digest="..."&gt;...&lt;/pin&gt;
            ...
        &lt;/pin-set&gt;
    &lt;/domain-config&gt;
    ...
    &lt;debug-overrides&gt;
        &lt;trust-anchors&gt;
            &lt;certificates src="..."/&gt;
            ...
        &lt;/trust-anchors&gt;
    &lt;/debug-overrides&gt;
&lt;/network-security-config&gt;
</pre>

<p>
  The following sections describe the syntax and other details of the file
  format.
</p>

<h3 id="network-security-config">
  &lt;network-security-config&gt;
</h3>

<dl class="xml">
  <dt>
    can contain:
  </dt>

  <dd>
    0 or 1 of <code><a href="#base-config">&lt;base-config&gt;</a></code><br>
    Any number of <code><a href=
    "#domain-config">&lt;domain-config&gt;</a></code><br>
    0 or 1 of <code><a href="#debug-overrides">&lt;debug-overrides&gt;</a></code>
  </dd>
</dl>

<h3 id="base-config">
  &lt;base-config&gt;
</h3>

<dl class="xml">
  <dt>
    syntax:
  </dt>
</dl>

<pre class="stx">
&lt;base-config <a href=
"#CleartextTrafficPermitted">cleartextTrafficPermitted</a>=["true" | "false"]&gt;
    ...
&lt;/base-config&gt;
</pre>
<dl class="xml">
  <dt>
    can contain:
  </dt>

  <dd>
    <code><a href="#trust-anchors">&lt;trust-anchors&gt;</a></code>
  </dd>

  <dt>
    description:
  </dt>

  <dd>
    The default configuration used by all connections whose destination is not
    covered by a <a href="#domain-config"><code>domain-config</code></a>.

<p>
  Any values that are not set use the platform default values. The default
  configuration for apps targeting Android 7.0 (API level 24) and higher is as
  follows:
</p>

<pre>
&lt;base-config cleartextTrafficPermitted="true"&gt;
    &lt;trust-anchors&gt;
        &lt;certificates src="system" /&gt;
    &lt;/trust-anchors&gt;
&lt;/base-config&gt;
</pre>
The default configuration for apps targeting Android 6.0 (API level 23) and
lower is as follows:
<pre>
&lt;base-config cleartextTrafficPermitted="true"&gt;
    &lt;trust-anchors&gt;
        &lt;certificates src="system" /&gt;
        &lt;certificates src="user" /&gt;
    &lt;/trust-anchors&gt;
&lt;/base-config&gt;
</pre>

  </dd>
</dl>

<h3 id="domain-config">&lt;domain-config&gt;</h3>
<dl class="xml">
<dt>syntax:</dt>
<dd>
<pre class="stx">&lt;domain-config <a href="#CleartextTrafficPermitted">cleartextTrafficPermitted</a>=["true" | "false"]&gt;
    ...
&lt;/domain-config&gt;</pre>
</dd>

<dt>Can Contain:</dt>

<dd>
1 or more <code><a href="#domain">&lt;domain&gt;</a></code>
<br/>0 or 1 <code><a href="#trust-anchors">&lt;trust-anchors&gt;</a></code>
<br/>0 or 1 <code><a href="#pin-set">&lt;pin-set&gt;</code></a>
<br/>Any number of nested <code>&lt;domain-config&gt;</code></dd>

<dt>Description</dt>
<dd>Configuration used for connections to specific destinations, as defined by
the {@code domain} elements.

<p>Note that if multiple {@code domain-config} elements cover a destination, the
configuration with the most specific (longest) matching domain rule is
used.</p></dd>
</dl>

<h3 id="domain">&lt;domain&gt;</h3>

<dl class="xml">
  <dt>
    syntax:
  </dt>

  <dd>
    <pre class="stx">
&lt;domain includeSubdomains=["true" | "false"]&gt;example.com&lt;/domain&gt;
</pre>
  </dd>

  <dt>
    Attributes:
  </dt>

  <dd>
    <dl class="attr">
      <dt>
        {@code includeSubdomains}
      </dt>

      <dd>
        If {@code "true"}, then this domain rule matches the domain and all
        subdomains, including subdomains of subdomains. Otherwise, the rule only
        applies to exact matches.
      </dd>
    </dl>
  </dd>

  <dt>
    Description:
  </dt>
</dl>

<h3 id="debug-overrides">&lt;debug-overrides&gt;</h3>

<dl class="xml">
  <dt>
    syntax:
  </dt>

  <dd>
    <pre class="stx">
&lt;debug-overrides&gt;
    ...
&lt;/debug-overrides&gt;
</pre>
  </dd>

  <dt>
    Can Contain:
  </dt>

  <dd>
    0 or 1 <code><a href="#trust-anchors">&lt;trust-anchors&gt;</a></code>
  </dd>

  <dt>
    Description:
  </dt>

  <dd>
    Overrides to be applied when <a href=
    "{@docRoot}guide/topics/manifest/application-element.html#debug">android:debuggable</a>
    is {@code "true"}, which is normally the case for non-release builds
    generated by IDEs and build tools. Trust anchors specified in {@code
    debug-overrides} are added to all other configurations, and certificate
    pinning is not performed when the server's certificate chain uses one of
    these debug-only trust anchors. If <a href=
    "{@docRoot}guide/topics/manifest/application-element.html#debug">android:debuggable</a>
    is {@code "false"}, then this section is completely ignored.
  </dd>
</dl>

<h3 id="trust-anchors">&lt;trust-anchors&gt;</h3>
<dl class="xml">
  <dt>
    syntax:
  </dt>

  <dd>
    <pre class="stx">
&lt;trust-anchors&gt;
...
&lt;/trust-anchors&gt;
</pre>
  </dd>

  <dt>
    Can Contain:
  </dt>

  <dd>
    Any number of <code><a href="#certificates">&lt;certificates&gt;</a></code>
  </dd>

  <dt>
    Description:
  </dt>

  <dd>
    Set of trust anchors for secure connections.
  </dd>
</dl>


<h3 id="certificates">&lt;certificates&gt;</h3>
<dl class="xml">
<dt>syntax:</dt>
<dd><pre class="stx">&lt;certificates src=["system" | "user" | "<i>raw resource</i>"]
              overridePins=["true" | "false"] /&gt;
</pre></dd>
<dt>description:</dt>
<dd>Set of X.509 certificates for {@code trust-anchors} elements.</dd>

<dt>attributes:</dt>
<dd><dl class="attr">
<dt>{@code src}</dt>
<dd>
The source of CA certificates. Each certificate can be one of the following:
<ul>
  <li>a raw resource ID pointing to a file containing X.509 certificates.
  Certificates must be encoded in DER or PEM format. In the case of PEM
  certificates, the file <em>must not</em> contain extra non-PEM data such as
  comments.
  </li>

  <li>{@code "system"} for the pre-installed system CA certificates
  </li>

  <li>{@code "user"} for user-added CA certificates
  </li>
</ul>
</dd>

<dt>{@code overridePins}</dt>
<dd>
  <p>
    Specifies if the CAs from this source bypass certificate pinning. If {@code
    "true"}, then pinning is not performed on certificate chains which are
    signed by one of the CAs from this source. This can be useful for debugging
    CAs or for testing man-in-the-middle attacks on your app's secure traffic.
  </p>

  <p>
    Default is {@code "false"} unless specified in a {@code debug-overrides}
    element, in which case the default is {@code "true"}.
  </p>
</dd>
</dl>
</dd>


<h3 id="pin-set">&lt;pin-set&gt;</h3>

<dl class="xml">
  <dt>
    syntax:
  </dt>

  <dd>
<pre class="stx">
&lt;pin-set expiration="date"&gt;
...
&lt;/pin-set&gt;
</pre>
  </dd>

  <dt>
    Can Contain:
  </dt>

  <dd>
    Any number of <code><a href="#pin">&lt;pin&gt;</a></code>
  </dd>

  <dt>
    Description:
  </dt>

  <dd>
    A set of public key pins. For a secure connection to be trusted, one of the
    public keys in the chain of trust must be in the set of pins. See
    <code><a href="#pin">&lt;pin&gt;</a></code> for the format of pins.
  </dd>

  <dt>
    Attributes:
  </dt>

  <dd>
    <dl class="attr">
      <dt>
        {@code expiration}
      </dt>

      <dd>
        The date, in {@code yyyy-MM-dd} format, on which the pins expire, thus
        disabling pinning. If the attribute is not set, then the pins do not
        expire.
        <p>
          Expiration helps prevent connectivity issues in apps which do not get
          updates to their pin set, such as when the user disables app updates.
        </p>
      </dd>
    </dl>
  </dd>
</dl>

<h3 id="pin">&lt;pin&gt;</h3>
<dl class="xml">
  <dt>
    syntax:
  </dt>

  <dd>
<pre class="stx">
&lt;pin digest=["SHA-256"]&gt;base64 encoded digest of X.509
    SubjectPublicKeyInfo (SPKI)&lt;/pin&gt;
</pre>
  </dd>

  <dt>
    Attributes:
  </dt>

  <dd>
    <dl class="attr">
      <dt>
        {@code digest}
      </dt>

      <dd>
        The digest algorithm used to generate the pin. Currently, only
        {@code "SHA-256"} is supported.
      </dd>
    </dl>
  </dd>
</dl>