Android is a modern mobile platform that was designed to be truly open. Android applications make use of advanced hardware and software, as well as local and served data, exposed through the platform to bring innovation and value to consumers. To protect that value, the platform must offer an application environment that ensures the security of users, data, applications, the device, and the network.
Securing an open platform requires a robust security architecture and rigorous security programs. Android was designed with multi-layered security that provides the flexibility required for an open platform, while providing protection for all users of the platform.
Android was designed with developers in mind. Security controls were designed to reduce the burden on developers. Security-savvy developers can easily work with and rely on flexible security controls. Developers less familiar with security will be protected by safe defaults.
Android was designed with device users in mind. Users are provided visibility into how applications work, and control over those applications. This design includes the expectation that attackers would attempt to perform common attacks, such as social engineering attacks to convince device users to install malware, and attacks on third-party applications on Android. Android was designed to both reduce the probability of these attacks and greatly limit the impact of the attack in the event it was successful.
This documentation outlines the goals of the Android security program, describes the fundamentals of the Android security architecture, and answers the most pertinent questions for system architects and security analysts. This document focuses on the security features of Android's core platform and does not discuss security issues that are unique to specific applications, such as those related to the browser or SMS application. Recommended best practices for building Android devices, deploying Android devices, or developing applications for Android are not the goal of this document and are provided elsewhere.
Android provides an open source platform and application environment for mobile devices.
The sections and pages below describe the security features of the Android platform. Figure 1 summarizes the security components and considerations of the various levels of the Android software stack. Each component assumes that the components below are properly secured. With the exception of a small amount of Android OS code running as root, all code above the Linux Kernel is restricted by the Application Sandbox.
Figure 1: Android software stack.
The main Android platform building blocks are:
Device Hardware: Android runs on a wide range of hardware configurations including smart phones, tablets, and set-top-boxes. Android is processor-agnostic, but it does take advantage of some hardware-specific security capabilities such as ARM v6 eXecute-Never.
Android Operating System: The core operating system is built on top of the Linux kernel. All device resources, like camera functions, GPS data, Bluetooth functions, telephony functions, network connections, etc. are accessed through the operating system.
Android Application Runtime: Android applications are most often written in the Java programming language and run in the Dalvik virtual machine. However, many applications, including core Android services and applications are native applications or include native libraries. Both Dalvik and native applications run within the same security environment, contained within the Application Sandbox. Applications get a dedicated part of the filesystem in which they can write private data, including databases and raw files.
Android applications extend the core Android operating system. There are two primary sources for applications:
Pre-Installed Applications: Android includes a set of pre-installed applications including phone, email, calendar, web browser, and contacts. These function both as user applications and to provide key device capabilities that can be accessed by other applications. Pre-installed applications may be part of the open source Android platform, or they may be developed by an OEM for a specific device.
User-Installed Applications: Android provides an open development environment supporting any third-party application. Google Play offers users hundreds of thousands of applications.
Google provides a set of cloud-based services that are available to any compatible Android device. The primary services are:
Google Play: Google Play is a collection of services that allow users to discover, install, and purchase applications from their Android device or the web. Google Play makes it easy for developers to reach Android users and potential customers. Google Play also provides community review, application license verification, application security scanning, and other security services.
Android Updates: The Android update service delivers new capabilities and security updates to Android devices, including updates through the web or over the air (OTA).
Application Services: Frameworks that allow Android applications to use cloud capabilities such as (backing up) application data and settings and cloud-to-device messaging (C2DM) for push messaging.
These services are not part of the Android Open Source Project and are out of scope for this document. But they are relevant to the security of most Android devices, so a related security document titled “Google Services for Android: Security Overview” is available.