RSA crypto example

Crypto.java

package com.volnoboy.util;

import sun.security.rsa.RSAPublicKeyImpl;

import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;

public class Crypto {

    private final String RSA = "RSA";

    private final int KEY_SIZE = 3072;

    public static void main(String [] args) throws Exception {
        Crypto crypto = new Crypto();
        KeyPair keyPair = crypto.buildKeyPair();
        PublicKey pubKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

        byte [] encrypted = crypto.encrypt(privateKey, "This is secret a message...");
        System.out.println(new String(encrypted));

        byte[] secret = crypto.decrypt(pubKey, encrypted);
        System.out.println(new String(secret));
    }

    public String decrypt(BigInteger n, BigInteger e,  byte [] encrypted) throws Exception {
        RSAPublicKeyImpl publicKey = new RSAPublicKeyImpl(n, e);
        return new String(decrypt(publicKey, encrypted));
    }

    private KeyPair buildKeyPair() throws NoSuchAlgorithmException {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(RSA);
        keyPairGenerator.initialize(KEY_SIZE);
        return keyPairGenerator.genKeyPair();
    }

    private byte[] encrypt(PrivateKey privateKey, String message) throws Exception {
        Cipher cipher = Cipher.getInstance(RSA);
        cipher.init(Cipher.ENCRYPT_MODE, privateKey);
        return cipher.doFinal(message.getBytes());
    }

    private byte[] decrypt(PublicKey publicKey, byte [] encrypted) throws Exception {
        Cipher cipher = Cipher.getInstance(RSA);
        cipher.init(Cipher.DECRYPT_MODE, publicKey);
        return cipher.doFinal(encrypted);
    }
}