Java RSA 공개 키 암호 화 비밀 키 복호화

package com.lee.utils;

import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;
import java.util.Date;

import javax.crypto.Cipher;

public class RSAUtil {

    private final static String PUBLIC_KEY_PATH = "c:/publicKeyFile";
    private final static String PRIVATE_KEY_PATH = "c:/privateKeyFile";

    /**
     *        
     */
    private static void geration(){
        KeyPairGenerator keyPairGenerator;
        try {
            keyPairGenerator = KeyPairGenerator.getInstance("RSA");
            SecureRandom secureRandom = new SecureRandom(new Date().toString().getBytes()); 
            keyPairGenerator.initialize(1024, secureRandom); 
            KeyPair keyPair = keyPairGenerator.genKeyPair(); 
            byte[] publicKeyBytes = keyPair.getPublic().getEncoded(); 
            FileOutputStream fos = new FileOutputStream(PUBLIC_KEY_PATH);  
            fos.write(publicKeyBytes);  
            fos.close(); 
            byte[] privateKeyBytes = keyPair.getPrivate().getEncoded(); 
            fos = new FileOutputStream(PRIVATE_KEY_PATH);  
            fos.write(privateKeyBytes);  
            fos.close(); 
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }  
    }
    
    /**
     *     
     * @param filename
     * @return
     * @throws Exception
     */
    public static PublicKey getPublicKey(String filename) throws Exception { 
        File f = new File(filename); 
        FileInputStream fis = new FileInputStream(f);  
        DataInputStream dis = new DataInputStream(fis); 
        byte[] keyBytes = new byte[(int)f.length()];
        dis.readFully(keyBytes);  
        dis.close();
        X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes); 
        KeyFactory kf = KeyFactory.getInstance("RSA");  
        return kf.generatePublic(spec); 
    } 
    
    
    
    /**
     *     
     * @param filename
     * @return
     * @throws Exception
     */
    public static PrivateKey getPrivateKey(String filename)throws Exception { 
        File f = new File(filename); 
        FileInputStream fis = new FileInputStream(f); 
        DataInputStream dis = new DataInputStream(fis); 
        byte[] keyBytes = new byte[(int)f.length()]; 
        dis.readFully(keyBytes); 
        dis.close(); 
        PKCS8EncodedKeySpec spec =new PKCS8EncodedKeySpec(keyBytes); 
        KeyFactory kf = KeyFactory.getInstance("RSA"); 
        return kf.generatePrivate(spec); 
      } 

    public static void main(String[] args) {
        
        geration();
          
        String input = "!!!hello world!!!"; 
        RSAPublicKey pubKey;
        RSAPrivateKey privKey;
        byte[] cipherText;
        Cipher cipher;
        try {
            cipher = Cipher.getInstance("RSA");         
            pubKey = (RSAPublicKey) getPublicKey(PUBLIC_KEY_PATH);
            privKey = (RSAPrivateKey) getPrivateKey(PRIVATE_KEY_PATH);
             
            cipher.init(Cipher.ENCRYPT_MODE, pubKey); 
            cipherText = cipher.doFinal(input.getBytes()); 
            //       
            System.out.println("cipher: " + new String(cipherText));         
            //     
            cipher.init(Cipher.DECRYPT_MODE, privKey);  
            byte[] plainText = cipher.doFinal(cipherText); 
            System.out.println("publickey: " + Base64.getEncoder().encode(cipherText));
            System.out.println("plain : " + new String(plainText));
        } catch (Exception e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        } 
    } 
}