OneTimePad Encryption

Question

I'm working on encrypted text using ascii value and I have this code:

import java.util.*;
public class OneTimePad{
   public static void main(String[] args){

        Scanner _user_ = new Scanner(System.in);  //Scanner Obj
    
        System.out.print(" Enter your Message : ");
        String Message = _user_.next();
        System.out.print(" Enter your Key : ");
        String Key = _user_.next();
        
        char Fnal;
        int Total;

         for(int l = 0 , m = 0; (l < Message.length() && m < Key.length()); l++,m++){   
            Total = (int)Message.charAt(l) + (int)Key.charAt(m);
           
            if((Total >=65 && Total <= 90) || (Total >= 97 && Total <=122 )){
                    System.out.print("Case 1");
                    Fnal = (char)Total;
                    System.out.print(Fnal);
            }else{
                System.out.print("Case 2");
                int a    = Total % 26;
                Fnal = (char)a;
                System.out.print(Fnal);
            }
        }
    }
}

Here is my output:

Enter your Message : hello

Enter your Key : hihih

Why only this two lines are printed on console? I don't see any error.

UPDATE

Here's my new code:

for(int l = 0 , m = 0; (l < Message.length() && m < Key.length()); l++,m++) {   
  Total = (int)Message.charAt(l) + (int)Key.charAt(m);
  //char s = Message.charAt(l);
  char dos = Message.charAt(l);
  String comp = String.valueOf(dos);

  if (comp.contains("ABCDEFGHIJKLMNOPQRSTUVWXYZ")){
    if(Total >=65 && Total <= 90){
      Fnal = (char)Total;
      System.out.print(Fnal);
    }else{
       int a    = Total % 26 + 65 ;
       Fnal = (char)a;
       System.out.print(Fnal);
    }
  }
}

Why it didn't Working?

It is because the results of addition is out-of-range of `(Total >=65 && Total <= 90) || (Total >= 97 && Total <=122 )` and therefore only control characters (character code less than 32) are printed. What is your desired behavior? — MikeCAT, Jul 30 '20 at 16:57
I am printing encrypted text using ascii value , i can resolve it. — sketch hacker, Jul 30 '20 at 17:06

Calaf · Accepted Answer · 2020-07-30T20:05:36.863

0

Not every integer has a visible character associated with it. You can use this simple method to print a list of integer and the relative char:

public static void printChars(){
    for (int i=0; i<1000; i++){
        System.out.println(i+" -> "+(char)i);
    }//for
}//printChars

So, why you don't see any output? Lets try with an example.

Enter your Message: a

Enter your Key: s

(int)Message.charAt(l) will be 97;
(int)Key.charAt(m) will be 115;
Finally, Total = (int)Message.charAt(l) + (int)Key.charAt(m) will be 212.

The two conditions Total >=65 && Total <= 90 and Total >= 97 && Total <=122 are not verified, so we have to see what happens in the "else" block.

int a = Total % 26 will be 4

As you can see by using the previous method printChars(), no visible character is associated with the number 4, therefore nothing is shown as output.

Tip: try to use some numeric input, for example

Enter your Message: 0

Enter your Key: 3

Total will be 48+51=99

The conditions are verified, so we have to go in the "if" block. The output will be (int)99, so we will see:

c

UPDATE

In your new code, first of all you have to define Total and Fnal as int. For example:

int Total = (int)Message.charAt(l) + (int)Key.charAt(m);

The main error is the use of contains(...).

If you write comp.contains("ABCDEFGHIJKLMNOPQRSTUVWXYZ"), you say that the string must have ABCDEFGHIJKLMNOPQRSTUVWXYZ as a substring (and not "A or B or C ...").

Probably you need a Pattern, and you can read a similar question here: Check if String contains only letters

edited Jul 30 '20 at 20:05

answered Jul 30 '20 at 17:46

Calaf

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Thanks a lot , it is very usefull for me. – sketch hacker Jul 30 '20 at 18:40
@sketchhacker Glad to have been helpful! If my answer has solved your problem, you can select it as "accepted" by clicking on the "v" button to the left of my answer. :D – Calaf Jul 30 '20 at 18:50
Hey , please check again , i edited my code , and please resolve my code. – sketch hacker Jul 30 '20 at 19:42
Thanks a lot Again – sketch hacker Jul 30 '20 at 20:10
Hey ,, i posted a question please tell me that the logic is right or not. – sketch hacker Jul 31 '20 at 19:51
It's work's fine , but my friend is telling that the logic is wrong , – sketch hacker Aug 01 '20 at 04:08
What is the logic you should follow? Is there a trace for this homework? The code reflects your comments, so if the logic is that the code is right. – Calaf Aug 01 '20 at 06:35

score 0 · Answer 2 · answered Jul 31 '20 at 19:50

import java.util.Scanner;
public class Onetimepad{
    public static void main(String[] args){
    
    Scanner _user_ = new Scanner(System.in);    // A Scanner Obj for to take input from user.
                            // System.in is to writing something on console
    
       // Take Message and key from user
    
    System.out.print(" Enter Message : ");
    String Message = _user_.next();

    System.out.print(" Enter Key ");
    String Key = _user_.next();

    // Converting each String latter into Character . And finding that latter's ascii value and 
    // And add that value to key's ascii value , and if it is greater than max than % 26.

    if (Message.length() == Key.length())
      { 
    for(int i = 0 , j = 0 ; i < Message.length() && j < Key.length() ; i++,j++)
    {
        char chmsg = Message.charAt(i);      // "V" = 'V'    
        char chkey = Key.charAt(j);    // "D" = 'D' 
        
        int chpr = (int)chmsg + (int)chkey; 
        
        if(chpr >= 65 && chpr <= 90)
        {
                 System.out.print((char)chpr);
        }
        else
        {
             chpr = chpr % 26+ 65;
             System.out.print((char)chpr);
        }
    } 
    
      }
    else
    {
      System.out.print(" Length of Message and Key is not same : ");
    }

}
} 


// What it is write code and the logic is right.
//Please Tell, It's a OneTimePad Encryption.

OneTimePad Encryption

2 Answers2