Question

1. A company that wants to send data over the Internet will use an encryption program to ensure data security. All data will be transmitted as four-digit integers. The application should read a four-digit integer entered by the user and encrypt it as follows:  Replace each digit with the remainder of the new value divided by 10 by adding 6 to the digit. Then replace the number in the first digit with the third, and the number in the second digit with the fourth. Print the encrypted integer on the screen.  Write a separate application where an encrypted four-digit integer is entered and decrypted (reversing the encryption scheme) and finds the original number.

Note: code should be written in Java Language.

Answer 1

Summary:

The program wriiten here is very simple, just go through the comments and print statements for better understanding.

Note:- This program works perfectly as per your requirement but there is no proper way to reverse the encryption method given in question to decrypt the value.

---------------------------------------------Encryption.java----------------------------------------

import java.util.Scanner;

public class Encryption {
    public static int encrypt(int number) {

        int[] digits = new int[4];
        for (int i = 0; i < 4; i++) {
            digits[i] = ((number % 10) + 6) % 10; // replace each digit with remainder of new value divided by 10 by adding 6 to the digit.
            number = number / 10;
        }

        // Replacing digit 1 with digit 3 and digit 2 with digit 4
        String str = "" + digits[1] + digits[0] + digits[3] + digits[2];
        return Integer.parseInt(str);
    }

    public static int decrypt(int encryptedNumber) {
        int[] digits = new int[4];
        int temp = 0;
        for (int i = 0; i < 4; i++) {
            temp = (encryptedNumber % 10);
            if (temp == 0) {
                digits[i] = 10 - 6;
            }
            else if (temp == 2) {
                digits[i] = 6;
            } else if (temp == 5) {
                digits[i] = 9;
            } else if (temp == 4) {
                digits[i] = 8;
            } else if (temp == 3) {
                digits[i] = 7;
            } else if (temp == 6) {
                digits[i] = 0;
            } else if (temp == 1) {
                digits[i] = 5;
            } else
                digits[i] = temp - 6;
            encryptedNumber = encryptedNumber / 10;
        }

        System.out.println("" + digits[3] + digits[2] + digits[1] + digits[0]);

        String str = "" + digits[1] + digits[0] + digits[3] + digits[2];
        return Integer.parseInt(str);
    }

    public static void main(String args[]) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter 4 digit number to encrypt");
        int number = scanner.nextInt();
        int encryptedNumber = encrypt(number);
        System.out.println("After Encryption: " + encryptedNumber);
        int decriptedNumber = decrypt(encryptedNumber);
        String result = String.valueOf(decriptedNumber);
        if (result.length()!=4)
            System.out.println("After Decryption: 0" + decriptedNumber);
        else
            System.out.println("After Decryption: " + decriptedNumber);
    }
}

Both encrypt and decrypt methods are implemented in the same class Encryption.

Code Screenshot:

Output:

Its one of the most difficult problem to revert the modulos of two number as their is no direct answers for that.

I tried by best to solve this problem to work perfectly correct.

Please rate thumbs up if you like the answer.

Thanks you!!!!