Question

Write a java program to encrypt and decrypt a message. The user should be able to choose between a Caesar cipher or a Vigenere cipher for their message. Use JOptionPane for user input.

Answer 1

Code

import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class EncryptDecrypt
{
public static void main(String[] args)
{
int userChoice,shift,enryptDecryptChoice;
String plainText,cipherText,msg;
String vignerkey;
JFrame f;
f=new JFrame();
do
{
userChoice=getUserInput("1. Ceaser Cipher 2. Vigenere cipher 3. Exit");
switch(userChoice)
{
case 1:
enryptDecryptChoice=getUserInput("1. Encryption 2. Decryption ");
if(enryptDecryptChoice==1)
{
shift=getUserInput("Enter the shift: ");
plainText=JOptionPane.showInputDialog("Enter the plain Text. ");
cipherText=encryptCeaser(plainText, shift);
msg="The cipher text is: "+cipherText;
JOptionPane.showMessageDialog(f,msg);
}
else if(enryptDecryptChoice==2)
{
shift=getUserInput("Enter the shift: ");
cipherText=JOptionPane.showInputDialog("Enter the encrypted Text. ");
plainText=decryptCeaser(cipherText, shift);
msg="The plaintext is: "+plainText;
JOptionPane.showMessageDialog(f,msg);
}
break;
case 2:
enryptDecryptChoice=getUserInput("1. Encryption 2. Decryption ");
if(enryptDecryptChoice==1)
{
plainText=JOptionPane.showInputDialog("Enter the plain Text. ");
vignerkey=JOptionPane.showInputDialog("Enter the key: ");
cipherText=encryptVigenere(plainText, vignerkey);
msg="The cipher text is: "+cipherText;
JOptionPane.showMessageDialog(f,msg);
}
else if(enryptDecryptChoice==2)
{
cipherText=JOptionPane.showInputDialog("Enter the encrypted Text. ");
vignerkey=JOptionPane.showInputDialog("Enter the key: ");
plainText=decryptVigenere(cipherText, vignerkey);
msg="The plaintext is: "+plainText;
JOptionPane.showMessageDialog(f,msg);
}
break;
case 3:
break;
default:
JOptionPane.showMessageDialog(f,"Invalid Choice. Please try again.");
break;
}
}while(userChoice!=3);
  
}

private static int getUserInput(String msg) {
return Integer.parseInt(JOptionPane.showInputDialog(msg));
}
public static String encryptCeaser(String plaintext,int shift)
{
char alphabet;
String ciphertext="";
for(int i=0; i < plaintext.length();i++)
{
// Shift one character at a time
alphabet = plaintext.charAt(i);
  
// if alphabet lies between a and z
if(alphabet >= 'a' && alphabet <= 'z')
{
// shift alphabet
alphabet = (char) (alphabet + shift);
// if shift alphabet greater than 'z'
if(alphabet > 'z') {
// reshift to starting position
alphabet = (char) (alphabet+'a'-'z'-1);
}
ciphertext = ciphertext + alphabet;
}
  
// if alphabet lies between 'A'and 'Z'
else if(alphabet >= 'A' && alphabet <= 'Z') {
// shift alphabet
alphabet = (char) (alphabet + shift);
  
// if shift alphabet greater than 'Z'
if(alphabet > 'Z') {
//reshift to starting position
alphabet = (char) (alphabet+'A'-'Z'-1);
}
ciphertext = ciphertext + alphabet;
}
else {
ciphertext = ciphertext + alphabet;   
}
  
}
return ciphertext;
}
public static String decryptCeaser(String ciphertext,int shift)
{
String decryptMessage = "";
for(int i=0; i < ciphertext.length();i++)
{
// Shift one character at a time
char alphabet = ciphertext.charAt(i);
// if alphabet lies between a and z
if(alphabet >= 'a' && alphabet <= 'z')
{
// shift alphabet
alphabet = (char) (alphabet - shift);
  
// shift alphabet lesser than 'a'
if(alphabet < 'a') {
//reshift to starting position
alphabet = (char) (alphabet-'a'+'z'+1);
}
decryptMessage = decryptMessage + alphabet;
}
// if alphabet lies between A and Z
else if(alphabet >= 'A' && alphabet <= 'Z')
{
// shift alphabet
alphabet = (char) (alphabet - shift);
  
//shift alphabet lesser than 'A'
if (alphabet < 'A') {
// reshift to starting position
alphabet = (char) (alphabet-'A'+'Z'+1);
}
decryptMessage = decryptMessage + alphabet;
}
else
{
decryptMessage = decryptMessage + alphabet;
}
}
return decryptMessage;
}
  
public static String encryptVigenere(String text, final String key)
{
String res = "";
text = text.toUpperCase();
for (int i = 0, j = 0; i < text.length(); i++)
{
char c = text.charAt(i);
if (c < 'A' || c > 'Z')
continue;
res += (char) ((c + key.charAt(j) - 2 * 'A') % 26 + 'A');
j = ++j % key.length();
}
return res;
}

public static String decryptVigenere(String text, final String key)
{
String res = "";
text = text.toUpperCase();
for (int i = 0, j = 0; i < text.length(); i++)
{
char c = text.charAt(i);
if (c < 'A' || c > 'Z')
continue;
res += (char) ((c - key.charAt(j) + 26) % 26 + 'A');
j = ++j % key.length();
}
return res;
}
}

outputs

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