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document default connections

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Daniel Micay 2019-05-09 18:12:02 -04:00
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@ -40,6 +40,71 @@
<a href="#auditor"></a>
</h2>
<p>See the <a href="https://attestation.app/tutorial">tutorial page on the site for the attestation sub-project</a>.</p>
<h2 id="default-connections">
Default connections
<a href="#default-connections"></a>
</h2>
<p>GrapheneOS makes connections to the outside world to test connectivity, detect
captive portals and download updates. No data varying per user / installation is sent
in these connections. There aren't analytics / telemetry in GrapheneOS.</p>
<p>The expected default connections by GrapheneOS (including all base system apps) are the following:</p>
<ul>
<li>
<p>The GrapheneOS Updater app fetches update metadata from
https://seamlessupdate.app/DEVICE-CHANNEL approximately once every four hours
when connected to a permitted network for updates.</p>
<p>Users can control which types of connections the Updater app will use, and
although it's strongly recommended to always leave it enabled it can be
disabled.</p>
</li>
<li>
<p>On devices with a Qualcomm baseband (which provides GPS), when location
functionality is being used,
<a href="https://en.wikipedia.org/wiki/GPS_signals#Almanac">GPS almanacs</a>
are downloaded from https://xtrapath1.izatcloud.net/xtra3grc.bin,
https://xtrapath2.izatcloud.net/xtra3grc.bin or
https://xtrapath3.izatcloud.net/xtra3grc.bin. GrapheneOS has modified all
references to these servers to use HTTPS rather than a mix of HTTP and HTTPS.</p>
</li>
<li>
<p>Connectivity checks designed to mimic a web browser user agent are performed
by using HTTP and HTTPS to fetch standard URLs generating an HTTP 204 status
code. This is used to detect when internet connectivity is lost on a network,
which triggers fallback to other available networks if possible. These checks
are designed to detect and handle captive portals which substitute the
expected empty 204 response with their own web page. These need use a very
common domain and URL in order to bypass whitelisting systems only permitting
access to common domains / URLs so a domain like grapheneos.org would likely
be inadequate. GrapheneOS leaves these set to the standard four URLs to blend
into the crowd of billions of other Android devices with and without Google
Mobile Services performing the same empty GET requests. For privacy reasons,
it isn't desirable to stand out from the crowd and changing these URLs or even
disabling the feature will likely reduce your privacy by giving your device a
more unique fingerprint. GrapheneOS aims to appear like any other common
mobile device on the network.</p>
<ul>
<li>HTTPS: https://www.google.com/generate_204</li>
<li>HTTP: http://connectivitycheck.gstatic.com/generate_204</li>
<li>HTTP fallback: http://www.google.com/gen_204</li>
<li>HTTP other fallback: http://play.googleapis.com/generate_204</li>
</ul>
<p>Standard AOSP user agent for the GET request:</p>
<p>Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.32 Safari/537.36</p>
<p>No query / data is sent and the response is unused beyond checking the response code.</p>
</li>
<li>
<p>DNS connectivity and functionality tests</p>
</li>
<li>
<p>DNS resolution for other connections</p>
</li>
</ul>
<p>Similar connectivity checks are also performed by the hardened Chromium browser (Vanadium).</p>
</div>
<footer>
<a href="/"><img src="https://grapheneos.org/logo.png" width="512" height="512" alt=""/>GrapheneOS</a>