RSA的应用

RSA是一种非对称加密算法。现在，很多登陆表单的密码的都采用RSA加密，例如京东中的登陆使用公钥对密码进行加密。

Base64编码

apache.commons-codex包提供了许多编码格式转换，例如Base64。

以下为Base64编码表
使用commons-codec进行Base64对字符串进行编码与解码的程序如下：

<dependency>
  <groupId>commons-codec</groupId>
  <artifactId>commons-codec</artifactId>
  <version>1.10</version>
</dependency>

package com.qian.encoded;

import org.apache.commons.codec.binary.Base64;

public class Base64Coded {
	public static void main(String[] args) {
		String string = "qianyang123";
		//编码
		String encode = encode(string.getBytes());
		System.out.println(string + "\t编码后的字符串为：" + encode);
		//解码
		String decode = decode(encode.getBytes());
		System.out.println(encode + "\t字符串解码后为：" + decode);
	}
	//base64 解码
    public static String decode(byte[] bytes) {  
        return new String(Base64.decodeBase64(bytes));  
    }  
  
    //base64 编码
    public static String encode(byte[] bytes) {  
        return new String(Base64.encodeBase64(bytes));  
    }  
}

程序的输出结果为：

qianyang123	编码后的字符串为：cWlhbnlhbmcxMjM=
cWlhbnlhbmcxMjM=	字符串解码后为：qianyang123

RSA加密与解密

使用RSA一般需要产生公钥和私钥，当采用公钥加密时，使用私钥解密；采用私钥加密时，使用公钥解密。以下为Java程序：

package com.yinhai.lipan.rsa;

import org.apache.commons.codec.binary.Base64;
import javax.crypto.Cipher;
import java.security.*;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

/**
 * Hello world!
 *
 */
public class App 
{
    private static Map<Integer,String> keyMap=new HashMap<>();
    public static void main( String[] args ) throws Exception {
        //生成公钥和私钥
        getKeyPair();
        //加密字符串
        String password="123456";
        System.out.println("随机生成的公钥为："+keyMap.get(0));
        System.out.println("随机生成的私钥为："+keyMap.get(1));
        String passwordEn=encrypt(password,keyMap.get(0));
        System.out.println(password+"\t加密后的字符串为："+passwordEn);
        String passwordDe=decrypt(passwordEn,keyMap.get(1));
        System.out.println("还原后的字符串为："+passwordDe);
    }
    /**
     * 随机生成密钥对
     * @throws NoSuchAlgorithmException
     */
    public static void getKeyPair() throws Exception {
        //KeyPairGenerator类用于生成公钥和密钥对，基于RSA算法生成对象
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
        //初始化密钥对生成器，密钥大小为96-1024位
        keyPairGen.initialize(1024,new SecureRandom());
        //生成一个密钥对，保存在keyPair中
        KeyPair keyPair = keyPairGen.generateKeyPair();
//        RSAPublicKey  privateKey = (RSAPublicKey) keyPair.getPrivate();//得到私钥
//        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();//得到公钥
        PrivateKey privateKey = keyPair.getPrivate();//得到私钥
        PublicKey publicKey = keyPair.getPublic();//得到公钥
//得到公钥字符串
        String publicKeyString=new String(Base64.encodeBase64(publicKey.getEncoded()));
        //得到私钥字符串
        String privateKeyString=new String(Base64.encodeBase64(privateKey.getEncoded()));
        //将公钥和私钥保存到Map
        keyMap.put(0,publicKeyString);//0表示公钥
        keyMap.put(1,privateKeyString);//1表示私钥
    }
    /**
     * RSA公钥加密
     *
     * @param str
     *            加密字符串
     * @param publicKey
     *            公钥
     * @return 密文
     * @throws Exception
     *             加密过程中的异常信息
     */
    public static String encrypt(String str,String publicKey) throws Exception {
        //base64编码的公钥
        byte[] decoded = Base64.decodeBase64(publicKey);
        RSAPublicKey pubKey= (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(decoded));
        //RAS加密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE,pubKey);
        String outStr=Base64.encodeBase64String(cipher.doFinal(str.getBytes("UTF-8")));
        return outStr;
    }

    /**
     * RSA私钥解密
     *
     * @param str
     *            加密字符串
     * @param privateKey
     *            私钥
     * @return 铭文
     * @throws Exception
     *             解密过程中的异常信息
     */
    public static String decrypt(String str,String privateKey) throws Exception {
        //Base64解码加密后的字符串
        byte[] inputByte = Base64.decodeBase64(str.getBytes("UTF-8"));
        //Base64编码的私钥
        byte[] decoded = Base64.decodeBase64(privateKey);
        PrivateKey priKey = KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(decoded));
        //RSA解密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE,priKey);
        String outStr=new String(cipher.doFinal(inputByte));
        return outStr;

    }
}

 在程序中，我们首先利用genKeyPair()函数生成公钥和私钥并将其保存到Map集合中。然后，基于产生的公钥对明文进行加密。针对已经已经加密的密文，我们再次使用私钥解密，得到明文。
上述程序的输出结果为：

随机生成的公钥为：MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCcjCMNuYGDhMD6ekWrKAZU4yE2Bj2mhJn6hJLiw6mpyu6sXITjbqyt+ZCpgmHNTrEYxaRPYTdrKTAEynl28Sk6pzquXEEk4oHivFcDZiDOam8JuyYlT1zDRs/muWtyv1hrDPZA0/EvTH6WCHIxToVYRvLDRH4/TB5u2MPAGKMx3wIDAQAB
随机生成的私钥为：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
123456	加密后的字符串为：iOtM4l+nrkePMxEcLeCa6n7jw1VwiWwtC1o6m0DpDowpsbZ7Pm1ZL2isb+TkoZU0uCgq6T3AJW7GzZ/3oESrQQwKjXHVA6yH3BfAJvXfw9uKUJIudOYpvgIn+1zvw3hsocuYiWLBARInZV+40leHl0nVfv2EcmxsEhKuOr5xFcM=
还原后的字符串为：123456