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 <p>Trusty is a set of software components supporting a Trusted Execution
 Environment (TEE) on mobile devices.</p>

 <p>Trusty consists of:</p>

 <ul>
   <li>An operating system (the Trusty OS) that runs on a processor intended to
 provide a TEE
   <li>Drivers for the Android kernel (Linux) to facilitate communication with
 applications running under the Trusty OS
   <li>A set of libraries for Android systems software to facilitate communication
 with trusted applications executed within the Trusty OS using the kernel
 drivers
 </ul>

 <p><strong>Important</strong>: Trusty and the Trusty API are subject
 to change.</p>

 <p>For information about the Trusty API, see the <a
 href="trusty-ref.html">API Reference</a>.</p>

 <h2 id=uses_examples>Uses and examples</h2>

 <p>Any TEE OS (not just Trusty) can be used for TEE implementations.</p>

 <p>A TEE processor is typically a separate microprocessor in the system or a
 virtualized instance of the main processor. The TEE processor is isolated from
 the rest of the system using memory and I/O protection mechanisms supported by
 the hardware.</p>

 <p>TEE processors have become a mainstay in today's mobile devices. The main
 processor on these devices is considered "untrusted" and cannot access certain
 areas of RAM, hardware registers and fuses where secret data (such as
 device-specific cryptographic keys) is stored by the manufacturer. Software
 running on the main processor delegates any operations that require use of
 secret data to the TEE processor.</p>

 <p>The most widely known example of this in the Android ecosystem
 is the <a href="/devices/drm.html">DRM framework</a> for
 protected content. Software running on the TEE processor can access
 device-specific keys required to decrypt protected content. The main processor
 sees only the encrypted content, providing a high level of security and
 protection against software-based attacks.</p>

 <p>There are many other uses for a TEE such as mobile payments, secure banking,
 full-disk encryption, multi-factor authentication, device reset protection,
 replay-protected persistent storage, wireless display ("cast") of protected
 content, secure PIN and fingerprint processing, and even malware detection.</p>

 <p>Trusty provides APIs for developing two classes of applications:</p>

 <ul>
   <li>Trusted applications or services that run on the TEE processor
   <li>Normal/untrusted applications that run on the main processor and use services
 provided by Trusted applications
 </ul>

 <p>Software running on the main processor can use Trusty APIs to connect to
 trusted applications and exchange arbitrary messages with them, just like a
 network service over IP. It is up to the application to determine the data
 format and semantics of these messages using an app-level protocol. Reliable
 delivery of messages is guaranteed by the underlying Trusty infrastructure (in
 the form of drivers running on the main processor), and the communication is
 completely asynchronous.</p>

 <h2 id=trusted_applications_and_services>Trusted applications and services</h2>

 <p>Trusted applications run as isolated processes under the Trusty OS kernel. Each
 process runs in its own virtual memory sandbox utilizing the MMU capabilities
 of the TEE processor. The kernel schedules these processes using a
 priority-based, round-robin scheduler driven by a secure timer tick. In the
 current version of Trusty, all Trusty applications share the same priority.</p>

 <p>Applications for the Trusty OS can be written in C/C++ (C++ support is
 limited), and they have access to a small C library. The <code>main()</code>
 function currently does not take any arguments. System call stubs are provided
 in native assembly code as part of this library, so system calls can be
 accessed by name.</p>

 <h3 id=language_threading>Language and threading support</h3>

 <p>All Trusty applications are single-threaded; multithreading in Trusty userspace
 currently is unsupported.</p>

 <h3 id=application_structure>Application structure</h3>

 <p>Trusty applications initialize once during load and reside in memory until the
 TEE processor is reset. Trusty currently does not support dynamic loading and
 unloading of applications.</p>

 <p>Trusted applications are written as <strong>event-driven servers</strong>
 waiting for commands from other applications or from applications running on
 the main processor. Trusted applications can also be clients of other trusted
 server applications. Events described in the following API sections will be
 delivered to trusted applications by the Trusty kernel.</p>

 <h2 id=third-party_trusty_applications>Third-party Trusty applications</h2>

 <p>Currently all Trusty applications are developed by a single party and packaged
 with the Trusty kernel image. The entire image is signed and verified by the
 bootloader during boot. Third-party application development is not supported in
 this version of Trusty.</p>

 <p>Although the Trusty OS enables the development of new applications, doing so
 must be exercised with extreme care; each new application increases the area of
 the trusted computing base (TCB) of the system. Trusted applications can access
 device secrets and can perform computations or data transformations using them.</p>

 <p>The ability to develop new applications that run in the TEE opens up many
 possibilities for innovation. However, due to the very definition of TEE, these
 applications cannot be distributed without some form of <strong>trust</strong> attached.
 Typically this comes in the form of a digital signature by an entity
 trusted by the user of the product on which the application runs.</p>

 <h2 id=downloading_building>Downloading and building Trusty</h2>

 <p>You can find the Trusty implementation in the Android Open Source Project (AOSP) here:<br/>
 <a href="https://android-review.googlesource.com/#/admin/projects/?filter=trusty">https://android-review.googlesource.com/#/admin/projects/?filter=trusty</a></p>

 <p>The Trusty kernel branches on AOSP are here:<br/>
 <a href="https://android.googlesource.com/kernel/common/+/android-trusty-3.10">https://android.googlesource.com/kernel/common/+/android-trusty-3.10</a><br/>
 <a href="https://android.googlesource.com/kernel/common/+/android-trusty-3.18">https://android.googlesource.com/kernel/common/+/android-trusty-3.18</a></p>

 <p>To make Trusty, run the following commands (assuming the Android toolchain is already in the path):</p>
 <pre>
 $ repo init -u https://android.googlesource.com/trusty/manifest
 $ repo sync
 $ make -j24 generic-arm64
 </pre>

 <p>You may select another supported build target from: <code>device/*/*/project/*</code></p>

   </body>
 </html>
	<html devsite>
	<head>
	<title>Trusty TEE</title>
	<meta name="project_path" value="/_project.yaml" />
	<meta name="book_path" value="/_book.yaml" />
	</head>
	<body>
	<!--
	Copyright 2017 The Android Open Source Project

	Licensed under the Apache License, Version 2.0 (the "License");
	you may not use this file except in compliance with the License.
	You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->



	<p>Trusty is a set of software components supporting a Trusted Execution
	Environment (TEE) on mobile devices.</p>

	<p>Trusty consists of:</p>

	<ul>
	<li>An operating system (the Trusty OS) that runs on a processor intended to
	provide a TEE
	<li>Drivers for the Android kernel (Linux) to facilitate communication with
	applications running under the Trusty OS
	<li>A set of libraries for Android systems software to facilitate communication
	with trusted applications executed within the Trusty OS using the kernel
	drivers
	</ul>

	<p><strong>Important</strong>: Trusty and the Trusty API are subject
	to change.</p>

	<p>For information about the Trusty API, see the <a
	href="trusty-ref.html">API Reference</a>.</p>

	<h2 id=uses_examples>Uses and examples</h2>

	<p>Any TEE OS (not just Trusty) can be used for TEE implementations.</p>

	<p>A TEE processor is typically a separate microprocessor in the system or a
	virtualized instance of the main processor. The TEE processor is isolated from
	the rest of the system using memory and I/O protection mechanisms supported by
	the hardware.</p>

	<p>TEE processors have become a mainstay in today's mobile devices. The main
	processor on these devices is considered "untrusted" and cannot access certain
	areas of RAM, hardware registers and fuses where secret data (such as
	device-specific cryptographic keys) is stored by the manufacturer. Software
	running on the main processor delegates any operations that require use of
	secret data to the TEE processor.</p>

	<p>The most widely known example of this in the Android ecosystem
	is the <a href="/devices/drm.html">DRM framework</a> for
	protected content. Software running on the TEE processor can access
	device-specific keys required to decrypt protected content. The main processor
	sees only the encrypted content, providing a high level of security and
	protection against software-based attacks.</p>

	<p>There are many other uses for a TEE such as mobile payments, secure banking,
	full-disk encryption, multi-factor authentication, device reset protection,
	replay-protected persistent storage, wireless display ("cast") of protected
	content, secure PIN and fingerprint processing, and even malware detection.</p>

	<p>Trusty provides APIs for developing two classes of applications:</p>

	<ul>
	<li>Trusted applications or services that run on the TEE processor
	<li>Normal/untrusted applications that run on the main processor and use services
	provided by Trusted applications
	</ul>

	<p>Software running on the main processor can use Trusty APIs to connect to
	trusted applications and exchange arbitrary messages with them, just like a
	network service over IP. It is up to the application to determine the data
	format and semantics of these messages using an app-level protocol. Reliable
	delivery of messages is guaranteed by the underlying Trusty infrastructure (in
	the form of drivers running on the main processor), and the communication is
	completely asynchronous.</p>

	<h2 id=trusted_applications_and_services>Trusted applications and services</h2>

	<p>Trusted applications run as isolated processes under the Trusty OS kernel. Each
	process runs in its own virtual memory sandbox utilizing the MMU capabilities
	of the TEE processor. The kernel schedules these processes using a
	priority-based, round-robin scheduler driven by a secure timer tick. In the
	current version of Trusty, all Trusty applications share the same priority.</p>

	<p>Applications for the Trusty OS can be written in C/C++ (C++ support is
	limited), and they have access to a small C library. The <code>main()</code>
	function currently does not take any arguments. System call stubs are provided
	in native assembly code as part of this library, so system calls can be
	accessed by name.</p>

	<h3 id=language_threading>Language and threading support</h3>

	<p>All Trusty applications are single-threaded; multithreading in Trusty userspace
	currently is unsupported.</p>

	<h3 id=application_structure>Application structure</h3>

	<p>Trusty applications initialize once during load and reside in memory until the
	TEE processor is reset. Trusty currently does not support dynamic loading and
	unloading of applications.</p>

	<p>Trusted applications are written as <strong>event-driven servers</strong>
	waiting for commands from other applications or from applications running on
	the main processor. Trusted applications can also be clients of other trusted
	server applications. Events described in the following API sections will be
	delivered to trusted applications by the Trusty kernel.</p>

	<h2 id=third-party_trusty_applications>Third-party Trusty applications</h2>

	<p>Currently all Trusty applications are developed by a single party and packaged
	with the Trusty kernel image. The entire image is signed and verified by the
	bootloader during boot. Third-party application development is not supported in
	this version of Trusty.</p>

	<p>Although the Trusty OS enables the development of new applications, doing so
	must be exercised with extreme care; each new application increases the area of
	the trusted computing base (TCB) of the system. Trusted applications can access
	device secrets and can perform computations or data transformations using them.</p>

	<p>The ability to develop new applications that run in the TEE opens up many
	possibilities for innovation. However, due to the very definition of TEE, these
	applications cannot be distributed without some form of <strong>trust</strong> attached.
	Typically this comes in the form of a digital signature by an entity
	trusted by the user of the product on which the application runs.</p>

	<h2 id=downloading_building>Downloading and building Trusty</h2>

	<p>You can find the Trusty implementation in the Android Open Source Project (AOSP) here:<br/>
	<a href="https://android-review.googlesource.com/#/admin/projects/?filter=trusty">https://android-review.googlesource.com/#/admin/projects/?filter=trusty</a></p>

	<p>The Trusty kernel branches on AOSP are here:<br/>
	<a href="https://android.googlesource.com/kernel/common/+/android-trusty-3.10">https://android.googlesource.com/kernel/common/+/android-trusty-3.10</a><br/>
	<a href="https://android.googlesource.com/kernel/common/+/android-trusty-3.18">https://android.googlesource.com/kernel/common/+/android-trusty-3.18</a></p>

	<p>To make Trusty, run the following commands (assuming the Android toolchain is already in the path):</p>
	<pre>
	$ repo init -u https://android.googlesource.com/trusty/manifest
	$ repo sync
	$ make -j24 generic-arm64
	</pre>

	<p>You may select another supported build target from: <code>device///project/*</code></p>

	</body>
	</html>