Encryption with RSA

RSA is a asymmetric encryption algorithm. It has a public key used to encrypt and a private key used to decrypt.

Let us do the same example we did in the previous post, this time with RSA.

In your /src/org/confucius folder, create a class RSAEncryption.java, like this:

 package org.confucius;  
   
 import java.security.InvalidKeyException;  
 import java.security.Key;  
 import java.security.KeyPair;  
 import java.security.KeyPairGenerator;  
 import java.security.NoSuchAlgorithmException;  
   
 import javax.crypto.BadPaddingException;  
 import javax.crypto.Cipher;  
 import javax.crypto.IllegalBlockSizeException;  
 import javax.crypto.NoSuchPaddingException;  
   
 public class RSAEncryption {  
   
      public static void main(String[] args) {  
           String secretMessageString = "For your eyes only...";  
             
           try {  
                KeyPairGenerator kpg;  
                kpg = KeyPairGenerator.getInstance("RSA");  
                kpg.initialize(2048);  
                KeyPair kp = kpg.genKeyPair();  
                Key publicKey = kp.getPublic();  
                Key privateKey = kp.getPrivate();  
                  
             // Encrypt  
                Cipher encryptCipher = Cipher.getInstance("RSA");  
                encryptCipher.init(Cipher.ENCRYPT_MODE, publicKey);  
                byte[] secretMessage = secretMessageString.getBytes();  
                byte[] encryptedMessage = encryptCipher.doFinal(secretMessage);  
                System.out.println("Encrypted Message = " + new String(encryptedMessage));  
                  
                // Decrypt  
                Cipher decryptCipher = Cipher.getInstance("RSA");  
                decryptCipher.init(Cipher.DECRYPT_MODE, (Key) privateKey);  
                byte[] decryptedMessage = decryptCipher.doFinal(encryptedMessage);  
                System.out.println("Decrypted message = " + new String(decryptedMessage));  
   
           } catch (NoSuchAlgorithmException e) {  
                e.printStackTrace();  
           } catch (InvalidKeyException e) {  
                e.printStackTrace();  
           } catch (NoSuchPaddingException e) {  
                e.printStackTrace();  
           } catch (IllegalBlockSizeException e) {  
                e.printStackTrace();  
           } catch (BadPaddingException e) {  
                e.printStackTrace();  
           }  
      }  
   
 }  
   

If you run this program (R-click in navigator view, select Run As --> Java application) you will see the encrypted and decrypted string printed to the console.