Question

The given plaintext is “Feistel cipher structure uses the same algorithm for both encryption and decryption”. Write Java code to implement Shift cipher (Encryption and Decryption) and test your code on given plaintext. Your code must meet following conditions.

1. User must enter the value of key from command prompt and print it at command prompt.

2. Print the cipher text and the plaintext at the command prompt after encryption and decryption.

3. Test your algorithm for 5 different key values and please give screenshots of command prompt input and outputs.

Answer 1

import java.util.Scanner;
public class ShiftCipherText {
   static String encrypt(String s, int k) {
       String en = "";
       char ch;
       int x[] = new int[s.length()];
       for(int i = 0; i < s.length(); i++) {
           x[i] = s.charAt(i) - 65;
       }
       for(int i = 0; i < s.length(); i++) {
           x[i] = (x[i] + k) % 26;
           ch = (char)(x[i] + 65);
           en = en.concat(Character.toString(ch));
       }
       return en;
   }
   static String decrypt(String en, int k) {
       String dec = "";
       char ch;
       int y[] = new int[en.length()];
       for(int i = 0; i < en.length(); i++) {
           y[i] = en.charAt(i) - 65;
       }
       for(int i = 0; i < en.length(); i++) {
           y[i] = (y[i] + 26 - k) % 26;
           ch = (char)(y[i] + 65);
           dec = dec.concat(Character.toString(ch));
       }
       return dec;
   }

   public static void main(String[] args) {
       int k;
       String s, en, dec;
       Scanner sc = new Scanner(System.in);
       System.out.println("Enter the text to encode(all uppercase characters): ");
       s = sc.nextLine();      
       System.out.print("Enter the key( 0 - 25): " );
       k = sc.nextInt();
      
       System.out.println("Key: " + k);
       en = encrypt(s, k);
       System.out.println("Cipher Text: " + en);
       dec = decrypt(en, k);
       System.out.println("Plain Text: " + dec);      

   }

}