Android Overview

Android Overview

•Android (Google) is a widely anticipated open

source operating system for mobile devices, •Supporting

Bluetooth (wireless for short distance)

Wi-Fi (wireless for 150 feet indoors, 300 ft outdoors)

3G(200 kbits/sec) and 4G (100 Mbit -1Gbit/sec)

•Android software stack–Android Linux operating system–Middleware(Dalvik Runtime Optimized Java virtual machineVM, Java API) and Library(Phone, contact, GPS map, SQLite, OpenGL.)

Android Architecture

Linux kernel Layer

• Android relies on Linux kernel• Supplies management of security, memory

process, network, and drivers • Acts as an abstraction layer between the

hardware and the rest of the Android software stack

Library Layer

• System C libraries and function Libraries, supporting multimedia, web browser, SQLite... Native Services to hardware

• Android runtime Dalvik Virtual Machine

– Executes files in the Dalvik Executable (.dex) format Java core Libraries

– Provides most of the functionality of the Java programming language.

Java core libraries rely on the Dalvik VM and the underlying Linux kernel

Every Android application runs in its own process, with its own instance of the Dalvik virtual machine

Application Framework Layer• Simplify the reuse of components

– Applications can publish their capabilities and any other application may then make use of those capabilities

• Applications is a set of services – Views system, content providers, resources

managers such as• Activity Manager, manages the lifecycle of applications

and provides a common navigation backstack• Notification Manager, enables all applications to

display custom alerts in the status bar• Resource Manager, providing access to non-code

resources such as localized strings, graphics, and layout files

• Views, used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser

Applications Layer

• A set of core applications shipped with Android platform– an email client, SMS program, calendar, maps,

browser, contacts, and others• All written in Java• User applications are also here

Features of Android• Popularity (High market share)• AWAT • Enabled SMS• Enabled GPS• Cameras & microphones• Open source apps• Development with Java• Linux based• Short learning curve with IDE Java Eclipse IDE for

Android app development• Easy deployment to mobile device• Easy to distribute apps via Android Market Share app, Sell app, Download & reuse open source apps

Cont.

• Hot job market – Market for mobile software surges from $4.1

billion in 2009 to $17.5 billion by 2012– 2010 Dice.com survey: 60% for Android– Dice.com: mobile app developers made

$85,000 in 2010 and salaries expected to rise2

Limitations

• screen size

• battery life time

• processor capacity

• Slow network access and Web browser

• Input: soft keyboard, phone keypad, touch screen, or stylus

• Security

Android App software components

– Activity– Service– Broadcast Receiver– Intent– Content Provider

Android App Development Tutorial:http://www.slideserve.com/lyndon/android-development-tutorial

Activity

• Activities provide a user interface for one specific task, Basic component of most applications

• Most applications have several activities that start each other as needed

• Each is implemented as a subclass of the base Activity class

Service

• Services execute background processing, no visual interface

Ex: Downloads, Playing Music, TCP/UDP Server

• You can bind to an existing service, control its operation, and run in background

• Play music, alarm clock, etc.• Secured if using permissions• Callers may need to verify that service is the

correct one

Content provider

• Content providers are data storage facilities which supports data exchange between applications

• Make data available to other applications• Transfer data between applications in Android • Other applications use a ContentResolver

object to access the data provided via a ContentProvider

ContentProviders

• Generally SQL backend• Used to share content between apps• Access controlled through permission tags• Apps can be dynamically authorized access

control– Possible security hole

• Must protect against SQL injection– verify input using parameterization

Broadcast receivers

• Broadcast receivers act as mailboxes for messages from other applications. It receives and reacts to broadcast announcements

• If an app registered the receiver in adv., the event will notify and call back the registered software

• Ex: Low battery, power connected, shutdown, timezone changed, etc.

Broadcast receivers

• Act as receivers for multiple components• Provide secure IPC• Done by specifying permissions on

BroadcastReceiver regarding sender• Otherwise, behave like activities in terms of IPC

– Can’t define permission• Don’t send sensitive data

Component life cycle

• Activities– Can terminate itself via finish();– Can terminate other activities it started via

finishActivity();• Services

– Can terminate via stopSelf(); or Context.stopService();

• Content Providers– Are only active when responding to ContentResolvers

• Broadcast Receivers– Are only active when responding to broadcasts

Intent– Intent is a goal action component which takes care of

the process of inter-components communication (ICC)– Intent is simply a message object containing a

destination component address and data– Protection– Each application executes as its own user identity,

such that OS provides system-level isolation;

– Android middleware contains a reference monitor that mediates the inter-component communication (ICC).

Intent(cont.)

Intent action:– Start an Activity– Broadcast events or changes– Start, stop, resume. or communicate with

background Services– Access data held by ContentProviders– Call back to handle events– Carry data with Extras (key, value)

Android component activation• An intent is an object which can have a message content

and start Activities, services and broadcast receivers

- ContentProvider is started by ContentResolvers– An activity is started by Context.startActivity(Intent

intent) or Activity.startActivityForResult(Intent intent, int RequestCode)

– A service is started by Context.startService(Intent service)

– An application can initiate a broadcast by using an Intent in any of Context.sendBroadcast(Intent intent), Context.sendOrderedBroadcast(), and Context.sendStickyBroadcast()

Intent Filters

• Used to determine recipient of Intent

• Specify the main entrance for activities

• A user interface consists of a series of Activities

• Each Activity is a “screen”.

• Intent may leave a security flaw (hole)

– Solution: Intents explicitly define receiver

@2011 Mihail L. Sichitiu 24

Goal

• Understand applications and their components

• Concepts: – activity, – service, – broadcast receiver, – content provider, – intent, – AndroidManifest

@2011 Mihail L. Sichitiu 25

Applications

• Written in Java (it’s possible to write native code – will not cover that here)

• Good separation (and corresponding security) from other applications:– Each application runs in its own process– Each process has its own separate VM– Each application is assigned a unique Linux user

ID – by default files of that application are only visible to that application (can be explicitly exported)

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Application Components

• Activities – visual user interface focused on a single thing a user can do

• Services – no visual interface – they run in the background

• Broadcast Receivers – receive and react to broadcast announcements

• Content Providers – allow data exchange between applications

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Activities

• Basic component of most applications

• Most applications have several activities that start each other as needed

• Each is implemented as a subclass of the base Activity class

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Activities – The View

• Each activity has a default window to draw in (although it may prompt for dialogs or notifications)

• The content of the window is a view or a group of views (derived from View or ViewGroup)

• Example of views: buttons, text fields, scroll bars, menu items, check boxes, etc.

• View(Group) made visible via Activity.setContentView() method.

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Services

• Does not have a visual interface

• Runs in the background indefinitely

• Examples– Network Downloads– Playing Music– TCP/UDP Server

• You can bind to a an existing service and control its operation

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Broadcast Receivers

• Receive and react to broadcast announcements

• Extend the class BroadcastReceiver

• Examples of broadcasts:– Low battery, power connected, shutdown,

timezone changed, etc.– Other applications can initiate broadcasts

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Content Providers

• Makes some of the application data available to other applications

• It’s the only way to transfer data between applications in Android (no shared files, shared memory, pipes, etc.)

• Extends the class ContentProvider;• Other applications use a ContentResolver

object to access the data provided via a ContentProvider

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Intents

• An intent is an Intent object with a message content.• Activities, services and broadcast receivers are started

by intents. ContentProviders are started by ContentResolvers:– An activity is started by Context.startActivity(Intent intent) or

Activity.startActivityForResult(Intent intent, int RequestCode)– A service is started by Context.startService(Intent service)– An application can initiate a broadcast by using an Intent in any

of Context.sendBroadcast(Intent intent), Context.sendOrderedBroadcast(), and Context.sendStickyBroadcast()

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Shutting down components

• Activities– Can terminate itself via finish();– Can terminate other activities it started via finishActivity();

• Services– Can terminate via stopSelf(); or Context.stopService();

• Content Providers– Are only active when responding to ContentResolvers

• Broadcast Receivers– Are only active when responding to broadcasts

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Android Manifest

• Its main purpose in life is to declare the components to the system: <?xml version="1.0" encoding="utf-8"?>

<manifest . . . >    <application . . . >        <activity android:name="com.example.project.FreneticActivity"                  android:icon="@drawable/small_pic.png"                  android:label="@string/freneticLabel"                   . . .  >        </activity>        . . .    </application></manifest>

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Intent Filters• Declare Intents handled by the current application (in the

AndroidManifest):

<?xml version="1.0" encoding="utf-8"?><manifest . . . >    <application . . . >        <activity android:name="com.example.project.FreneticActivity"                  android:icon="@drawable/small_pic.png"                  android:label="@string/freneticLabel"                   . . .  >            <intent-filter . . . >                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>            <intent-filter . . . >                <action android:name="com.example.project.BOUNCE" />                <data android:mimeType="image/jpeg" />                <category android:name="android.intent.category.DEFAULT" />            </intent-filter>        </activity>        . . .    </application></manifest>

Shows in the Launcher and is the main activity to start

Handles JPEG images in some way

System level protection for Android app

• Each app runs as a unique user identity such that Android can limit the potential damage of programming flaws.

• Each app runs in own VM sandbox using unique UID

• Each app requests a simple permission label assignment model to restrict access to resources and other applications if necessary

• Ex. of permission: Internet, camera, GPS• Permission specifies an access policy to protect

its resources.

Android Permissions• All permission of Android’s policy are set at install time

and can’t change until the application is reinstalled.• Android’s permission only restricts access to

components and doesn’t currently provide information flow guarantees.

• A permission is listed in app’s manifest definition XML file.

• If a public component doesn’t explicitly declare any access permission, Android permits any application to access it.

• Component A’s ability to access components B and C is determined by comparing the access permission labels on B and C to the collection of permission labels assigned to application A.

Android App Signature• All Android applications must be signed, but are usually self-signed

• Why self signing?– Market ties identity to developer account– No CA in Google, Google does not have central

control over the app’s signature certificates– No applications are trusted.  No "magic key"

• What does signing determine?– Author-update– In signature schemes, the private key is used to sign

a app or message; anyone can check the signature using the public key.

Permissions Levels

• User can assign permissions to applications at

- normal

– dangerous– signature– signatureOrSystem

• http://developer.android.com/guide/developing/building/index.html#detailed-build

Reference1.http://www.businessweek.com/technology/content/oct2010/

tc20101020_639668.htm2. http://it-jobs.fins.com/Articles/SB129606993144879991/Mobile-

App-Developers-Wanted-at-Ad-Agencies3.http://www.gartner.com/it/page.jsp?id=14663134.http://developer.android.com/guide/developing/index.html5.Android Overview, http://www.google.com/url?

sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CEcQFjAG&url=http%3A%2F%2Fai.arizona.edu%2Fmis510%2Fslides%2FAndroid%2520Overview.ppt&ei=4HBXUNPvMuPe0QGm3oCYCg&usg=AFQjCNE2Li9vyh34rECKYDuOjKjI5pjyzw&sig2=E-wfIL1bPNJacCi6ZaAWCA

6. Mobile Application Security on Android, Originally presented by Jesse Burns at Black Hat 2009