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Unit - 1

Title

Introduction to Android​

1. History of Android​

1.1 Foundation and Android Inc.​

1.1.1 Android Inc. Origins​

  • Foundation: Android Inc. was founded in Palo Alto, California, in October 2003.
  • Founders: Andy Rubin, Rich Miner, Nick Sears, and Chris White.
  • Vision: Rubin described the project as having "tremendous potential in developing smarter mobile devices that are more aware of its owner's location and preferences".
  • Early Intentions: The company's initial goal was to develop an advanced operating system for digital cameras, which formed the basis of their pitch to investors in April 2004.

1.1.2 Acquisition by Google​

  • Acquisition Date: On August 17th, 2005, Google quietly acquired Android Incorporation for $50 million. Since then, it has been a subsidiary of Google Incorporation.
  • Motivation: Interestingly, the idea of making an open-source smartphone operating system that would rival Symbian, Apple iOS, and Microsoft Windows Mobile was initially the key reason Google was not attracted to it. Nevertheless, it is now considered one of Google's best acquisitions to date.

1.2 Key Dates​

  • October 2003: Android Inc. was founded.
  • July 2005: Google acquired Android Inc.
  • November 5th, 2007: OHA (Open Handset Alliance) was formed.
  • October 22nd, 2008: First Android Smartphone, the HTC Dream, was launched.
  • September 8th, 2020: Android OS’s Latest version, Android 11, was released.

2. Android Hardware and Software​

2.1 Android Hardware​

2.1.1 Supported Architectures​

  • Primary Platform: The main hardware platform for Android is ARM (the ARMv7 and ARMv8-A architectures).
  • x86 Support: x86 and x86-64 architectures are also officially supported in later versions.
    • The unofficial Android-x86 project provided support for x86 architectures ahead of the official support.
    • Since 2012, Android devices with Intel processors began to appear, including phones and tablets.
  • 64-bit Evolution: Android was first made to run on 64-bit x86. Since Android 5.0 ("Lollipop"), 64-bit variants of all platforms are supported in addition to the 32-bit variants.
  • RISC-V: An unofficial experimental port of the operating system to the RISC-V architecture was released in 2021.

2.2 Android Software Architecture​

2.2.1 Architecture Diagram​

2.2.2 Applications​

  • Definition: The top layer of the Android architecture.
  • Contents: Includes pre-installed applications (like home, contacts, camera, gallery, etc.) and third-party applications downloaded from the Play Store (like chat applications, games, etc.).
  • Execution: Runs within the Android runtime with the help of classes and services provided by the application framework.

2.2.3 Application Framework​

  • Definition: Provides several important classes used to create an Android application.
  • Features:
    • Provides a generic abstraction for hardware access.
    • Helps in managing the user interface with application resources.
    • Provides services to create particular classes that are helpful for application creation.
  • Components: Includes different types of services according to prerequisites:
    • Activity Manager
    • Notification Manager
    • View System
    • Package Manager

2.2.4 Android Runtime​

  • Definition: One of the most important parts of Android. It provides the base for the application framework and powers the application using core libraries.
  • Components:
    • Core Libraries: Enable the implementation of Android applications using standard JAVA or Kotlin programming languages.
    • Dalvik Virtual Machine (DVM):
      • Like Java Virtual Machine (JVM), DVM is a register-based virtual machine specially designed and optimized for Android to ensure a device can run multiple instances efficiently.
      • Depends on the Linux kernel layer for threading and low-level memory management.

2.2.5 Platform Libraries​

  • Definition: Includes various C/C++ core libraries and Java-based libraries providing support for Android development.
  • Key Libraries:
    • Media Library: Provides support to play and record audio and video formats.
    • Surface Manager: Responsible for managing access to the display subsystem.
    • SGL and OpenGL: Both cross-language, cross-platform application program interfaces (APIs) used for 2D and 3D computer graphics.
    • SQLite: Provides database support.
    • FreeType: Provides font support.
    • Web-Kit: Open source web browser engine that provides all the functionality to display web content and simplify page loading.
    • SSL (Secure Sockets Layer): Security technology to establish an encrypted link between a web server and a web browser.

2.2.6 Linux Kernel​

  • Definition: The heart of the Android architecture. It manages all available drivers (display, camera, Bluetooth, audio, memory, etc.) required during runtime.
  • Function: Provides an abstraction layer between the device hardware and other components of the Android architecture. It manages memory, power, devices, etc.
  • Key Features:
    • Security: Handles the security between the application and the system.
    • Memory Management: Efficiently handles memory management, providing freedom to develop apps.
    • Process Management: Allocates resources to processes whenever they need them.
    • Network Stack: Effectively handles network communication.
    • Driver Model: Ensures that the application works properly on the device, with hardware manufacturers responsible for building their drivers into the Linux build.

3. Android Security and Permission Models​

3.1 Understanding the Android Security Model​

3.1.1 User Isolation vs Traditional Linux​

  • Android takes advantage of user isolation but treats users differently than a traditional Linux system (desktop or server).
  • Traditional Linux: A UID is given to a physical user that logs in and executes shell commands, or to a system service (daemon) to limit damage if compromised over a network.
  • Android Sandboxing: Because mobile phones are personal devices, there is no need to register different physical users. The physical user is implicit.
  • Core Principle: In Android, UIDs are used to distinguish applications instead of physical users. This forms the foundational basis of Android’s application sandboxing.

3.1.2 Key Security Controls​

  • Permission Control: Determines what data and features an app can access.
  • Privilege Control: Allocates a separate PID (Process ID) to each app to enforce boundaries.

3.2 Security Mechanisms​

3.2.1 Application Sandbox​

  • Definition: Each Android app operates in its own sandbox, an isolated environment preventing it from accessing other apps' data and system resources without proper permissions.
  • User ID (UID): Each app is assigned a unique UID at install time. The Linux kernel enforces isolation by associating each UID with a specific app and its data.
  • File Permissions: By default, an app can only access its own files and directories. This ensures that even if an app is compromised, it cannot tamper with other apps or the system.

3.2.2 Permissions​

  • Definition: A mechanism controlling an app's access to system features and user data.
  • Manifest Declaration: Apps declare the permissions they need in their AndroidManifest.xml file.
  • Runtime Permissions: Since Android 6.0 (Marshmallow), sensitive permissions (e.g., access to camera, location) must be requested at runtime, allowing users to grant or deny them interactively.

3.2.3 Application Signing​

  • Definition: Each Android app must be signed with a developer's private key before it can be installed.
  • Signature Verification: During installation, the system verifies the signature against the developer's public key to ensure integrity and that it hasn't been tampered with.
  • Update Verification: For updates, the new version must be signed with the identical key as the original app, preventing unauthorized malicious updates.

3.2.4 Security-Enhanced Linux (SELinux)​

  • Definition: A mandatory access control (MAC) system that enhances the security of the Linux kernel.
  • Policies: SELinux enforces strict policies that define how processes can interact with each other and the system, helping to prevent privilege escalation and unauthorized access.
  • Enforcement Modes: Android uses SELinux in "enforcing mode," meaning policy violations are strictly blocked and logged.

3.2.5 Verified Boot​

  • Definition: Ensures that the device's software hasn’t been tampered with and only runs software verified by the manufacturer.
  • Boot Verification: During the boot process, each stage verifies the integrity and authenticity of the next stage (from the bootloader up to the system partition).
  • Rollback Protection: Prevents downgrading to a previous, potentially vulnerable version of the operating system.

3.2.6 Google Play Protect​

  • Definition: A security service that continuously scans devices and apps for harmful behavior.
  • App Scanning: Scans apps both in the Google Play Store and on users’ devices to detect and remove malicious applications.
  • SafetyNet: A set of APIs that help apps determine whether the device they're running on is secure and not tampered with.

3.2.7 Encryption and User Authentication​

  • Encryption: Ensures data stored on the device is protected from unauthorized access.
    • Full Disk Encryption: Encrypts all user data on the device.
    • File-Based Encryption: Introduced in Android 7.0 (Nougat), replacing Full Disk Encryption to encrypt individual files.
    • Encryption Keys: Managed by the Trusted Execution Environment (TEE), ensuring keys are protected and never exposed to the main OS.
  • User Authentication: Mechanisms to verify the user's identity.
    • Biometrics: Fingerprint, face recognition, and other methods.
    • Passwords/PINs/Patterns: Traditional authentication methods to unlock the device.

3.2.8 Network Security and Updates​

  • Network Security: Measures to protect data transmitted over networks.
    • HTTPS: Apps are highly encouraged to use HTTPS to encrypt data in transit.
    • Network Security Config: Allows developers to define strict network security settings in a configuration file, ensuring secure connections and preventing insecure traffic.
  • Security Updates: Regular updates to address vulnerabilities.
    • Monthly Security Patches: Google releases monthly patches to address known security vulnerabilities.
    • Project Treble: Aims to simplify and expedite the delivery of Android updates by separating the underlying vendor implementation from the Android OS framework.

4. Rooting (Android)​

4.1 Introduction to Rooting​

  • Definition: Rooting is the process of allowing users of the Android mobile operating system to attain privileged control (known as root access) over various Android subsystems.
  • Linux Comparison: Because Android is based on a modified Linux kernel, rooting gives similar administrative (superuser) permissions as found on Linux or Unix-like systems (like FreeBSD or macOS).
  • Goal: Often performed to overcome limitations imposed by carriers and hardware manufacturers.
  • Capabilities: Gives the ability to alter or replace system applications and settings, run specialized applications ("apps") that require administrator-level permissions, or perform inaccessible operations. It can also facilitate the complete removal and replacement of the operating system (usually with a newer custom ROM).

4.2 Checking Root Status​

  • Superuser Applications: The presence of applications like Kinguser or Superuser on the device is an obvious sign that the device has been rooted, as they manage access to superuser permissions.
    • These apps are installed as part of the rooting process and are also used to check the root status.
  • Settings Check: For some devices, a user can go to Settings -> "About Phone" to review software versions. Any irregularities in the software will be noted here.

4.3 Benefits of Android Rooting​

  • Custom ROMs: Install custom versions of Android (ROMs) for better performance, extended features, or newer versions of Android not officially available for the specific device.
  • Full Control: Complete access to the system files and settings allows for extensive, deep customization.
  • Remove Bloatware: Uninstall pre-installed apps (bloatware) that are typically non-removable on unrooted devices.
  • Advanced Apps: Run apps that require root access, offering advanced features like system-level backups, ad-blocking, and CPU overclocking.
  • Performance Enhancements: Adjust low-level system settings to improve battery life, increase performance, and heavily tweak hardware components.