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<title>Attestation compatibility guide | Articles | GrapheneOS</title>
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<main id="attestation-compatibility-guide">
<h1><a href="#attestation-compatibility-guide">Attestation compatibility guide</a></h1>
<p>Apps using SafetyNet attestation to check the authenticity/integrity of the OS can
support GrapheneOS by using the standard Android hardware attestation API and
permitting our official release signing keys. Android's
<a href="https://developer.android.com/training/articles/security-key-attestation">hardware
attestation API</a> provides a much stronger form of attestation than SafetyNet with
the ability to whitelist the keys of alternate operating systems. It also avoids an
unnecessary dependency on Google Play services and Google's SafetyNet servers.</p>
<p>Devices have been required to ship with hardware attestation support since Android
8. You can use hardware attestation on devices running Android 8 or later when the
<code>ro.product.first_api_level</code> system property isn't set to 25 or below,
which indicates they launched with Android 8 or later with hardware attestation
support as a mandatory feature. On older devices, you can continue using SafetyNet
attestation. Some low quality devices shipped broken implementations of hardware
attestation despite the requirement to have it working for CDD/CTS certification and
SafetyNet currently still passes on those devices wrongly claiming them to be CTS
certified. If you don't want to fail on those devices, then you can start with
hardware attestation and fall back to SafetyNet attestation or do both and accept
either passing as success.</p>
<p>After verifying the signature of the attestation certificate chain and extracting
the attestation metadata, you can enforce that <code>verifiedBootState</code> is
either <code>Verified</code> or <code>SelfSigned</code>. For the
<code>SelfSigned</code> case, you can check that <code>verifiedBootKey</code> matches
one of the official GrapheneOS verified boot keys. These are the base16-encoded
verified boot key fingerprints for the official GrapheneOS releases:</p>
<ul>
<li><code>0abddeda03b6ce10548c95e0bea196faa539866f929bcdf7eca84b4203952514</code>: Pixel 5a</li>
<li><code>36a99eab7907e4fb12a70e3c41c456bcbe46c13413fbfe2436adee2b2b61120f</code>: Pixel 5</li>
<li><code>dcec2d053d3ec4f1c9be414aa07e4d7d7cbd12040ad2f8831c994a83a0536866</code>: Pixel 4a (5G)</li>
<li><code>3f15fdcb82847fed97427ce00563b8f9ff34627070de5fdb17aca7849ab98cc8</code>: Pixel 4 XL</li>
<li><code>80ef268700ee42686f779a47b4a155fe1ffc2eedf836b4803caab8fa61439746</code>: Pixel 4</li>
<li><code>9f2454a1657b1b5ad7f2336b39a2611f7a40b2e0ddfd0d6553a359605928df29</code>: Pixel 4a</li>
<li><code>3f36e3482e1ff82986576552cb4fd08af09f8b09d3832314341e04c42d2919a4</code>: Pixel 3a XL</li>
<li><code>73d6c63a07610404fe16a4e07dd24e41a70d331e9d3ef7bba2d087e4761eb63a</code>: Pixel 3a</li>
<li><code>06dd526ee9b1cb92aa19d9835b68b4ff1a48a3ad31d813f27c9a7d6c271e9451</code>: Pixel 3 XL</li>
<li><code>0f9a9cc8ade73064a54a35c5509e77994e3aa37b6fb889dd53af82c3c570c5cf</code>: Pixel 3</li>
</ul>
<p>The <code>verifiedBootKey</code> field is binary data so you either need to encode
it as base16 to compare with these or convert these to binary. An easy approach is
storing the permitted key fingerprints in a set and enforcing that the verified boot
key is in the permitted set when <code>verifiedBootState</code> is
<code>SelfSigned</code>.</p>
<p>GrapheneOS regularly adds support for new devices so you should have a process for
regularly adding the new verified boot key fingerprints from this page.</p>
<p>The hardware attestation API also provides other useful information signed by the
hardware including the OS patch level, in a way that even an attacker exploiting the
OS after boot to gain root cannot trivially bypass. It's a better feature than the
SafetyNet API designed for the lowest common denominator.</p>
<p>GrapheneOS users are strongly encouraged to share this documentation with app
developers enforcing only being able to use the stock OS. Send an email to the
developers and leave a review of the app with a link to this information. Share it
with other users and create pressure to support GrapheneOS rather than locking users
into the stock OS without a valid security reason. GrapheneOS not only upholds the
app security model but substantially reinforces it, so it cannot be justified with
reasoning based on security, anti-fraud, etc.</p>
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