1

Android Introduction

Wifi p2p chat application

2

Goal

• Understand applications and their components

• Concepts: – activity,

– service,

– broadcast receiver,

– content provider,

– intent,

– AndroidManifest

– Accessing Hardware

– p2p

– Security - Encryption

– Code

– Layout

3

Applications

• Written in Java (it’s possible to write native code & html / javascript also)

• 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)

4

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

5

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

6

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.

7

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

8

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

9

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

10

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()

11

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

12

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>

13

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

Accessing Hardware - wifi

• package• android.net.wifi• Provides classes to manage Wi-Fi functionality on the device.

• The Wi-Fi APIs provide a means by which applications can communicate with the lower-level wireless stack that provides Wi-Fi network access. Almost all information from the device supplicant is available, including the connected network's link speed, IP address, negotiation state, and more, plus information about other networks that are available. Some other API features include the ability to scan, add, save, terminate and initiate Wi-Fi connections.

• Some APIs may require the following user permissions:

• ACCESS_WIFI_STATE• CHANGE_WIFI_STATE• CHANGE_WIFI_MULTICAST_STATE• Note: Not all Android-powered devices provide Wi-Fi functionality. If your application uses Wi-Fi, declare so with a

<uses-feature> element in the manifest file:

• <manifest ...>• <uses-feature android:name="android.hardware.wifi" />• ...• </manifest>

class use case provided by android

• Classes• ScanResult Describes information about a detected access point. • WifiConfiguration A class representing a configured Wi-Fi network, including the security configuration. • WifiConfiguration.AuthAlgorithm Recognized IEEE 802.11 authentication algorithms. • WifiConfiguration.GroupCipher Recognized group ciphers. • WifiConfiguration.KeyMgmt Recognized key management schemes. • WifiConfiguration.PairwiseCipher Recognized pairwise ciphers for WPA. • WifiConfiguration.Protocol Recognized security protocols. • WifiConfiguration.Status Possible status of a network configuration. • WifiEnterpriseConfig Enterprise configuration details for Wi-Fi. • WifiEnterpriseConfig.Eap The Extensible Authentication Protocol method used • WifiEnterpriseConfig.Phase2 The inner authentication method used • WifiInfo Describes the state of any Wifi connection that is active or is in the process of being set up. • WifiManager This class provides the primary API for managing all aspects of Wi-Fi connectivity. • WifiManager.MulticastLock Allows an application to receive Wifi Multicast packets. • WifiManager.WifiLock Allows an application to keep the Wi-Fi radio awake. • WifiManager.WpsCallback Interface for callback invocation on a start WPS action • WpsInfo A class representing Wi-Fi Protected Setup

p2p - Peer 2 Peer

Peer 2 Peer Networking is type of networking where there is no need of any centralized server , eachnode works as both server and client

Each node has particular ID assigned , by which they can identify internally , IP number for example , there is no central dns for assigning ID , depending on number of nodes , ID's are assigned

No Central Server is Required for P2p based application

Wifi basic vs Wifi Direct

• WIFI - BASIC (central acces point)• Conventional Wi-Fi networks are typically based on the

presence of controller devices known as wireless access points.

• All nodes are connect to this AP / Router

• WIFI - Direct (p2p based)• Wi-Fi Direct essentially embeds a software access point

("Soft AP"), into any device that must support Direct.The soft AP provides a version of Wi-Fi Protected Setup with its push-button or PIN-based setup.

Encryption

• Encryption is the process of encoding messages or information in such a way that only authorized parties can read it. Encryption does not of itself prevent interception, but denies the message content to the interceptor

keys in Encryption

• As shown in example suppose A send message Hello (encrypted with key)

• that message in communication channel will be %$#^^&%$#^**^% random

• Againg on B receiver side after DeCryption

the message becames hello

• Hence , person who is not authorised(does not have key) cannot read the message

AES - Advance Encry. Sys.

• AES is based on a design principle known as a substitution-permutation network, combination of both substitution and permutation, and is fast in both software and hardware.[10] Unlike its predecessor DES, AES does not use a Feistel network. AES is a variant of Rijndael which has a fixed block size of 128 bits, and a key size of 128, 192, or 256 bits. By contrast, the Rijndael specification per se is specified with block and key sizes that may be any multiple of 32 bits, both with a minimum of 128 and a maximum of 256 bits

• We can say it block sustitution system where 128 , 192 or 256 bits block are substituted to provide encryption

wifi direct app code

• Java code logic • chatbocactivity - Android Activity class• custombroadcastreciever - Android Broadcast Reciever• encryptor - Java Cypher • mainactivity - Android Activity class• mycustomservice - Android Service class

Layout Files• activity_chat_box - the screen where chat occurs• activity_main - Main home screen of app

Layout App

• Android uses various views & views groups to display user & interact with user

• Our Main use is List View

• Home screen utilisez list view to display peers

• And chat box screen display messages

screenshots

Main Home Chatbox activity

Citation

• Android Studio 1.0

• JDK 7

• Android SDK version 21

• Gradle built script

• Java for logic coding & defination

• xml for layout defination

• xml for manifest & security permission

• java cypher for encryptor class