Hands-on Lab Practice

Software Requirement

Android Studio

Android SDK

Tutorial: Generate and Save Keys

Use JAVA tool keytool.exe for Windows $keytool for Unix to generate Keystore on the server-side:

Open "Terminal" and run the following command

keytool -genkey -alias mydomain -keyalg RSA -keystore keystore.jks -keysize 2048

2. Create android projects for server and client

Server

Layout

In this lab, the main layout for the server contains a button to start the server to listen to the connection from clients; and the layout for the client contains a text box for users to input messages to send and buttons for sending messages and close a connection.

//main.xml

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context=".MainActivity">

<TextView

android:id="@+id/textview"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginBottom="348dp"

android:text="Client Message"

app:layout_constraintBottom_toBottomOf="parent"

app:layout_constraintHorizontal_bias="0.464"

app:layout_constraintLeft_toLeftOf="parent"

app:layout_constraintRight_toRightOf="parent" />

<Button

android:id="@+id/button"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Start Server"

tools:layout_editor_absoluteX="148dp"

tools:layout_editor_absoluteY="214dp"

tools:ignore="MissingConstraints"

android:onClick="connect"/>

</android.support.constraint.ConstraintLayout>

Server side

//MainActivity.java

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements DataDisplay {

TextView serverMessage;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

serverMessage = findViewById(R.id.textview);

}

public void connect(View view){

MyServer server = new MyServer(getBaseContext());

server.setEventListerner(this);

server.startListening();

}

public void Display(String message){

serverMessage.setText(""+message);

}

}

//MyServer.Java

import android.content.Context;

import android.os.Handler;

import android.os.Message;

import android.util.Log;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.net.ServerSocket;

import java.net.Socket;

import java.security.KeyStore;

import javax.net.ssl.KeyManagerFactory;

import javax.net.ssl.SSLContext;

import javax.net.ssl.SSLServerSocket;

public class MyServer {

Thread m_objThread;

ServerSocket m_server;

DataDisplay m_dataDisplay;

private static final int SERVER_PORT = 5000;

private static final String SERVER_KEY_PASSWORD = "123456";

private static final String SERVER_AGREEMENT = "TLS";

private static final String SERVER_KEY_MANAGER = "X509";

private static final String SERVER_KEY_KEYSTORE = "BKS";

Context ctx;

SSLServerSocket serverSocket;

public MyServer(Context context){

this.ctx = context;

}

public void setEventListerner(DataDisplay dataDisplay){

m_dataDisplay = dataDisplay;

}

public void startListening(){

m_objThread = new Thread(new Runnable() {

@Override

public void run() {

try{

SSLContext sslContext = SSLContext.getInstance(SERVER_AGREEMENT);

KeyManagerFactory keyManager = KeyManagerFactory.getInstance(SERVER_KEY_MANAGER);

KeyStore kks = KeyStore.getInstance(SERVER_KEY_KEYSTORE);

kks.load(ctx.getResources().openRawResource(R.raw.bksserver), SERVER_KEY_PASSWORD.toCharArray());

keyManager.init(kks,SERVER_KEY_PASSWORD.toCharArray());

sslContext.init(keyManager.getKeyManagers(),null,null);

serverSocket = (SSLServerSocket)sslContext.getServerSocketFactory().createServerSocket(SERVER_PORT);

if (serverSocket != null) Log.i("ServerSocket", "Server Socket is ready to accept!!");

Socket connectedSocket = serverSocket.accept();

Message clientMessage = Message.obtain();

ObjectInputStream ois = new ObjectInputStream(connectedSocket.getInputStream());

String strMessage = (String)ois.readObject();

clientMessage.obj = strMessage;

mHandler.sendMessage(clientMessage);

ObjectOutputStream oos = new ObjectOutputStream(connectedSocket.getOutputStream());

oos.writeObject("Hello Client");

ois.close();

oos.close();

m_server.close();

}catch (Exception e){

Message msg = Message.obtain();

msg.obj = e.getMessage();

mHandler.sendMessage(msg);

}

}

});

m_objThread.start();

}

Handler mHandler = new Handler(){

@Override

public void handleMessage(Message msg) {

m_dataDisplay.Display(msg.obj.toString());

}

};

}

//DataDisplay.Java

public interface DataDisplay {

void Display(String message);

}

// AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="com.smsd.arabin.smsd_server">

<uses-permission android:name="android.permission.INTERNET"/>

<application

android:allowBackup="true"

android:icon="@mipmap/ic_launcher"

android:label="@string/app_name"

android:roundIcon="@mipmap/ic_launcher_round"

android:supportsRtl="true"

android:theme="@style/AppTheme">

<activity android:name=".MainActivity">

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

</application>

</manifest>

//Client

//main.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context=".MainActivity">

<TextView

android:id="@+id/text"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignStart="@+id/button"

android:layout_alignParentTop="true"

android:layout_marginStart="7dp"

android:layout_marginTop="164dp"

android:text="Server Message"

tools:ignore="RtlCompat" />

<Button

android:id="@+id/button"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_centerInParent="true"

android:text="Start Client"

android:onClick="Start"/>

</RelativeLayout>

//Client side

//MainActivity.java

import android.content.Context;

import android.net.wifi.WifiInfo;

import android.net.wifi.WifiManager;

import android.os.Handler;

import android.os.Message;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.text.format.Formatter;

import android.util.Log;

import android.view.View;

import android.widget.TextView;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.security.KeyStore;

import javax.net.ssl.KeyManagerFactory;

import javax.net.ssl.SSLContext;

import javax.net.ssl.SSLSocket;

import javax.net.ssl.TrustManagerFactory;

public class MainActivity extends AppCompatActivity {

TextView serverMessage;

Thread m_objectThreadClient;

private static final String CLIENT_KEY_PASSWORD = "123456";

private static final String CLIENT_TRUST_PASSWORD = "123456";//

private static final String CLIENT_AGREEMENT = "TLS";// the protocol used

private static final String CLIENT_KEY_MANAGER = "X509";// key manager

private static final String CLIENT_TRUST_MANAGER = "X509";

private static final String CLIENT_KEY_KEYSTORE = "BKS";// key store，use

// BouncyCastle

private static final String CLIENT_TRUST_KEYSTORE = "BKS";//

private SSLSocket clientSocket;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

serverMessage = findViewById(R.id.text);

}

public void Start(View view){

m_objectThreadClient = new Thread(new Runnable() {

@Override

public void run() {

try{

SSLContext sslContext = SSLContext.getInstance(CLIENT_AGREEMENT);

// get the X509 key manager instance of KeyManagerFactory and

// TrustManagerFactory

KeyManagerFactory keyManager = KeyManagerFactory.getInstance(CLIENT_KEY_MANAGER);

TrustManagerFactory trustManager = TrustManagerFactory.getInstance(CLIENT_TRUST_MANAGER);

// get BKS

KeyStore kks = KeyStore.getInstance(CLIENT_KEY_KEYSTORE);

KeyStore tks = KeyStore.getInstance(CLIENT_TRUST_KEYSTORE);

// load certificate and key of client by reading the key and

// trustful certificate in the resources file

kks.load(getBaseContext().getResources().openRawResource(R.raw.bksclient), CLIENT_KEY_PASSWORD.toCharArray());

tks.load(getBaseContext().getResources().openRawResource(R.raw.cacerts), CLIENT_TRUST_PASSWORD.toCharArray());

// initial key manager

keyManager.init(kks, CLIENT_KEY_PASSWORD.toCharArray());

trustManager.init(tks);

// initial SSLContext

sslContext.init(keyManager.getKeyManagers(), trustManager.getTrustManagers(), null);

Log.i("SslActivity", "start ssl connecting");

WifiManager wifi = (WifiManager)getApplicationContext().getSystemService(Context.WIFI_SERVICE);

String ip;

if (wifi.isWifiEnabled()){

wifi.setWifiEnabled(true);

WifiInfo wifiInfo = wifi.getConnectionInfo();

ip = Formatter.formatIpAddress(wifiInfo.getIpAddress());

}else {

ip = "127.0.0.1";

}

clientSocket = (SSLSocket) sslContext.getSocketFactory().createSocket(ip,5000);

if(clientSocket!=null) Log.i("SslActivity", "ssl connected");

ObjectOutputStream oos = new ObjectOutputStream(clientSocket.getOutputStream());

oos.writeObject("Hello there");

Message serverMessage = Message.obtain();

ObjectInputStream ois = new ObjectInputStream(clientSocket.getInputStream());

String strMessage = (String)ois.readObject();

serverMessage.obj = strMessage;

mHandler.sendMessage(serverMessage);

oos.close();

ois.close();

}catch (Exception e){

e.printStackTrace();

}

}

});

m_objectThreadClient.start();

}

Handler mHandler = new Handler(){

@Override

public void handleMessage(Message msg) {

messageDisplay(msg.obj.toString());

}

};

private void messageDisplay(String s) {

serverMessage.setText(""+s);

}

}

//AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="com.smsd.arabin.smsd_client">

<uses-permission android:name="android.permission.INTERNET"/>

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>

<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>

<application

android:allowBackup="true"

android:icon="@mipmap/ic_launcher"

android:label="@string/app_name"

android:roundIcon="@mipmap/ic_launcher_round"

android:supportsRtl="true"

android:theme="@style/AppTheme">

<activity android:name=".MainActivity">

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

</application>

</manifest>

Why we need SSL?

The primary reason why SSL is used is to keep sensitive information sent across the Internet encrypted so that only the intended recipient can understand it. This is important because the information you send on the Internet is passed from computer to computer to get to the destination server. Any computer in between you and the server can see your credit card numbers, usernames and passwords, and other sensitive information if it is not encrypted with an SSL certificate. When an SSL certificate is used, the information becomes unreadable to everyone except for the server you are sending the information to. This protects it from hackers and identity thieves.

In addition to encryption, a proper SSL certificate also provides authentication. This means you can be sure that you are sending information to the right server and not to a criminal’s server.

Comparison between applications without SSL and with SSL