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5 min read Beginner Mobile

Android Architecture

Android architecture contains different components to support various device needs. The software is built upon an open-source Linux Kernel, comprising a collection of C/C++ libraries exposed through application framework services. Among all the components, the Linux Kernel provides the main functionality of operating system functions to smartphones, while the Dalvik Virtual Machine (DVM) provides a platform for running an Android application.

Main Components​

  1. Applications

    • Applications represent the top layer of the Android architecture.
    • Includes pre-installed applications like Home, Contacts, Camera, Gallery, etc., and third-party applications downloaded from the Play Store.
    • It runs within the Android runtime with the help of the classes and services provided by the application framework.

  2. Application Framework

    • Application Framework provides several important classes used to create an Android application.
    • Provides a generic abstraction for hardware access and manages the user interface with application resources.
    • Includes services like activity manager, notification manager, view system, package manager, etc.

  3. Application Runtime

    • Android Runtime environment is one of the most important parts of Android.
    • Contains components like core libraries and the Dalvik virtual machine (DVM).
    • Provides the base for the application framework and powers applications with the help of the core libraries.
    • DVM is optimized for Android to ensure that a device can run multiple instances efficiently.

  4. Platform Libraries

    • Includes various C/C++ core libraries and Java-based libraries for various functionalities.
    • Media library supports playing and recording audio and video formats.
    • Surface manager manages access to the display subsystem.
    • SGL and OpenGL are used for 2D and 3D computer graphics.
    • SQLite provides database support and FreeType provides font support.
    • Web-Kit provides functionality to display web content and simplify page loading.
    • SSL (Secure Sockets Layer) is security technology to establish an encrypted link between a web server and a web browser.

  5. Linux Kernel

    • Linux Kernel is the heart of the Android architecture.
    • Manages all available drivers required during runtime, such as display, camera, Bluetooth, audio, memory drivers, etc.
    • Provides an abstraction layer between device hardware and other components of the Android architecture.
    • Responsible for:
      • Security: The Linux kernel handles the security between the application and the system.
      • Memory Management: It efficiently handles memory management, providing freedom to develop apps.
      • Process Management: It manages processes well and allocates resources to processes when needed.
      • Network Stack: It effectively handles network communication.
      • Driver Model: It ensures proper functioning of device drivers and compatibility with hardware manufacturers.

A moible apk contains:​

  1. AndroidManifest.xml: This file contains information about the application, including its package name, version number, required permissions, and components such as activities, services, and broadcast receivers.
  2. Classes.dex: This file contains the compiled Java bytecode for the application’s classes, which are executed by the Android Runtime (ART).
  3. Resources.arsc: This file contains compiled resources such as strings, images, and layouts that are used by the application.
  4. lib/: This folder contains compiled native code libraries for specific device architectures, such as ARM or x86.
  5. META-INF/: This folder contains the manifest file, the certificate of the APK signature, and a list of all the files in the APK, along with their checksums.
  6. assets/: This folder contains additional application data files, such as sound and video files, that are not compiled into the APK.
  7. res/: This folder contains the application resources, such as layouts, strings, and images, in their original format before being compiled into the Resources.arsc file.
  8. Android System Files: This folder contains system-level files such as the Android runtime, framework libraries, and system components that the application may use.

Android Components and Security​

Activity​

  • Represents a single screen with a user interface in an Android application.
  • Entry point for user interaction.
  • Potential security issues: insecure data storage, input validation, authentication flaws.

Broadcast Receiver​

  • Listens for system-wide broadcast messages or intents.
  • Responds to system events.
  • Potential security issues: insecure broadcast handling, privilege escalation.

Intent​

  • Messaging object used to communicate between components.
  • Starts Activities, Services, delivers broadcasts, or passes data between components.
  • Potential security issues: intent spoofing, intent injection, insecure data passing.

Explicit Intents​

  • Used to start a specific component within the same application.
  • Requires specifying the target component's class or package name.
  • Example: Starting a new Activity within the app.

Implicit Intents​

  • Used to trigger actions based on an action string.
  • Does not specify the target component's name but defines an action to be performed.
  • Android system resolves the intent based on available components capable of handling the action.
  • Example: Opening a web page or sending an email.

Service​

  • Background component that performs long-running operations.
  • Runs tasks asynchronously without a user interface.
  • Potential security issues: insufficient authentication, denial of service (DoS), data leakage.

Content Provider​

  • Manages shared application data accessible by other applications or components.
  • Provides a standardized interface for accessing and manipulating data.
  • Potential security issues: insecure data exposure, insufficient access controls.

Manifest File (AndroidManifest.xml)​

  • Configuration file containing essential information about the application.
  • Declares components, permissions, and hardware requirements.
  • Potential security issues: excessive permissions, missing security controls.

WebView​

  • Embeds web content within an application.
  • Can execute JavaScript, load remote URLs, and interact with the DOM.
  • Potential security issues: JavaScript injection, XSS attacks, insecure communication.

Activity Manager​

  • Manages the lifecycle of application activities.
  • Controls the creation, starting, pausing, and stopping of activities.
  • Handles activity stacking and navigation within the application.