How to generate OTP Number with 6 digits

Question

What is an OTP number in a login authentication system? Is there any specific algorithm for generating OTP numbers using java (android). Or is an OTP something like random number? How can this be achieved, with optimization.

Answer 1

Please do not reinvent the wheel - especially in case of security and cryptography. You might end up in a really bad state.

Use algorithms, that the community agreed upon like the HOTP and TOTP algorithm specified by the Open Authentication Iniative. These algorithms are also used by the google authenticater and specified in these RFCs. Read them. They are simple.

http://tools.ietf.org/html/rfc4226

https://tools.ietf.org/html/rfc6238

Answer 2

I have the same difficulty to find simple rule about it.

There are a lot of content explaining about OTP like "Time Synchronized" etc..., however I was looking for a simple solution while keeping the system's security.

In my case I keep the 2FA (Two Factor Authentication), that already gives a lot of security.

A relevant info about JAVA for random generator (see: SecureRandom) Important if you want a unique number generation, avoiding repeats.

Examples:

https://www.securecoding.cert.org/confluence/display/java/MSC02-J.+Generate+strong+random+numbers

Details about it: http://resources.infosecinstitute.com/random-number-generation-java/

Based on examples above I implemented the following snippet:

public class SimpleOTPGenerator {


    protected SimpleOTPGenerator() {
    }

    public static String random(int size) {

        StringBuilder generatedToken = new StringBuilder();
        try {
            SecureRandom number = SecureRandom.getInstance("SHA1PRNG");
            // Generate 20 integers 0..20
            for (int i = 0; i < size; i++) {
                generatedToken.append(number.nextInt(9));
            }
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }

        return generatedToken.toString();
    }
}

Answer 3

First of all OTP stands for one time password it is used for the authentication and 
verification this is code is for java implemented in netbeans IDE
 You have to register on the msg91.com for the api genration and that gives free 250 
 msgs.
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Random;
import javax.swing.JOptionPane;
 public class SMS {
String num,otp;
SMS(String mob)
{
    num=mob;

}
 static String otpGenerator() 
{ 
    String numbers = "0123456789"; 
    String x="";
    Random rndm_method = new Random(); 
    char[] otp = new char[4]; 
    for (int i = 0; i <4; i++) 
    { 
        otp[i]=numbers.charAt(rndm_method.nextInt(numbers.length())); 
        x=x+otp[i];
    } 

    return x; 
}//this is the function for the random number generator for otp
 public void sms(String otp)
{
        try {

        String apiKey = "api key on msg91.com";
        String message = otp;
        String sender = "TESTIN";
        String numbers = num;
                    String a="http://api.msg91.com/api/sendhttp.php? 
          country=91&sender="+ sender +"&route=4&mobiles=" + numbers +"&authkey=api 
           key on msg91.com&message="+message+" ";
                    //System.out.println(a);
                    // Send data
        HttpURLConnection conn = (HttpURLConnection) new URL(a).openConnection();
        String data = apiKey + numbers + message + sender;
        conn.setDoOutput(true);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Content-Length", Integer.toString(data.length()));
        conn.getOutputStream().write(data.getBytes("UTF-8"));
        final BufferedReader rd = new BufferedReader(new 
         InputStreamReader(conn.getInputStream()));
        final StringBuffer stringBuffer = new StringBuffer();
        String line;
        while ((line = rd.readLine()) != null) {
            //stringBuffer.append(line);
                        //JOptionPane.showMessageDialog(null, "message"+line);
                        System.out.println("OTP SENT !");
        }
        rd.close();

        //return stringBuffer.toString();
    } catch (Exception e) {
                JOptionPane.showMessageDialog(null,e);

    }

}
//now you have to call this function and send your number as the parameter
 public Start() {
    this.setUndecorated(true);

    initComponents();

    jPasswordField1.setBackground(new Color(0, 0, 0, 0));

    jPasswordField1.setOpaque(false);  
    //jPasswordField1.setBorder(null); 
    this.setBounds(300, 200, 707, 390);
    SMS otp=new SMS("your number");
    x=otp.otpGenerator();
    otp.sms(x); 
    }

Answer 4

import java.util.*;

public class OTP2 {
  static char[] OTP(int len) {
    System.out.println("Generating OTP using random ()");
    System.out.print("Your OTP is:");

    // Using numeric values
    String numbers = "0123456789";

    // Using random method 
    Random rndm_method = new Random();
    char[] otp = new char[len];
    for(int i=0; i<len;i++) {
      // use of charAt() method : to get character value
      // use of nextInt() as it is scanning the value as int 
      otp[i] = numbers.charAt(rndm_method.nextInt(numbers.length()));
    }
    return otp;
  }

  public static void main(String args[]) {
    int length = 6;
    System.out.println(OTP(length));
  }
}

Answer 5

Check google authenticator. : https://github.com/google/google-authenticator it is open source project with OTP functionality

Source code for android app https://code.google.com/p/google-authenticator/source/browse/?repo=android

Here is source code for server side https://github.com/chregu/GoogleAuthenticator.php

Wikipedia article http://en.wikipedia.org/wiki/Time-based_One-time_Password_Algorithm

Answer 6

protected void onCreate(Bundle savedInstanceState)
 {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Random otp  =new Random();

        StringBuilder builder=new StringBuilder();
        for(int count=0; count<=10;count++) {
            builder.append(otp.nextInt(10));
        }
        Log.d("Number", " " + builder.toString());

        TextView txt = (TextView) findViewById(R.id.txt);

        txt.setText(builder.toString());
   }