[转]RSA实例

package com.lj.rsa;

import java.io.IOException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

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

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

@SuppressWarnings("restriction")
public class RSAHelper
{
	/**
	 * 得到公钥
	 * @throws IOException 
	 * @throws NoSuchAlgorithmException 
	 * @throws InvalidKeySpecException 
	 */

	public static PublicKey getPublicKey(String key) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException{
		byte[] keyBytes;

		keyBytes=(new BASE64Decoder()).decodeBuffer(key);

		X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);

		KeyFactory keyFactory=KeyFactory.getInstance("RSA");

		PublicKey publicKey=keyFactory.generatePublic(keySpec);


		return publicKey;
	}


	public static PrivateKey getPrivateKey(String key) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException{
		byte[] keyBytes;
		keyBytes= new BASE64Decoder().decodeBuffer(key);

		PKCS8EncodedKeySpec keySpec=new PKCS8EncodedKeySpec(keyBytes);
		KeyFactory keyFactory=KeyFactory.getInstance("RSA");
		PrivateKey privateKey=keyFactory.generatePrivate(keySpec);
		return privateKey;

	}

	public static String getKeyString(Key key){
		byte[] keyBytes=key.getEncoded();
		String s=new BASE64Encoder().encode(keyBytes);
		return s;
	}


	public static void main(String[] args) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException
	{
	//	System.out.println(RSAHelper.getPublicKey("hello"));

		KeyPairGenerator keyPairGen=KeyPairGenerator.getInstance("RSA");

		keyPairGen.initialize(1024);

		KeyPair keyPair=keyPairGen.generateKeyPair();

		System.out.println(keyPair); //null


		//公钥
		PublicKey publicKey=(RSAPublicKey)keyPair.getPublic();

		System.out.println(publicKey);

		//秘钥
		PrivateKey privateKey=keyPair.getPrivate();

		byte[] publicKeyBytes=publicKey.getEncoded();
		String publicKeyString=(new BASE64Encoder()).encode(publicKeyBytes);


		byte[] privateKeyBytes=privateKey.getEncoded();
		String privateKeyString=(new BASE64Encoder()).encode(privateKeyBytes);

		//加解密类
		Cipher cipher=Cipher.getInstance("RSA");

		//明文
		byte[] plainText="你好世界".getBytes();

		//加密
		cipher.init(Cipher.ENCRYPT_MODE, publicKey);
		byte[] enBytes=cipher.doFinal(plainText);

		//通过秘钥字符串得到秘钥
		publicKey=getPublicKey(publicKeyString);
		privateKey=getPrivateKey(privateKeyString);

		String encodedStr=new String(enBytes,"utf-8");
		System.out.println("加密密文为:\n"+encodedStr);





		//解密
		cipher.init(Cipher.DECRYPT_MODE, privateKey);

		byte[] deBytes=cipher.doFinal(enBytes);

		publicKeyString = getKeyString(publicKey);

	//	System.out.println("publicKeyString=\n"+publicKeyString);


		privateKeyString=getKeyString(privateKey);
		//	System.out.println("privateKeyString=\n"+privateKeyString);

		String s=new String(deBytes);
		System.out.println(s);

	}


}