JAVA上加密算法的例子（2在JAVA中的实现）

2.1. 相关

Diffie-Hellman密钥一致协议和DES程序需要JCE工具库的支持,可以到 http://java.sun.com/security/index.html  或是www.bt285.cn 下载JCE,并进行安装。简易安装把 jce1.2.1\lib 下的所有内容复制到 %java_home%\lib\ext下,如果没有ext目录自行建立,再把jce1_2_1.jar和sunjce_provider.jar添加到 CLASSPATH内,更详细说明请看相应用户手册

2.2. 消息摘要MD5和SHA的使用

使用方法:

首先用生成一个MessageDigest类,确定计算方法

java.security.MessageDigest alga=java.security.MessageDigest.getInstance("SHA-1");

添加要进行计算摘要的信息

alga.update(myinfo.getBytes());

计算出摘要

byte[] digesta=alga.digest();

发送给其他人你的信息和摘要

其他人用相同的方法初始化,添加信息,最后进行比较摘要是否相同

algb.isEqual(digesta,algb.digest())

相关AIP

java.security.MessageDigest 类

static getInstance(String algorithm)

返回一个MessageDigest对象,它实现指定的算法

参数:算法名,如 SHA-1 或MD5

void update (byte input)

void update (byte[] input)

void update(byte[] input, int offset, int len)

添加要进行计算摘要的信息

byte[] digest()

完成计算,返回计算得到的摘要(对于MD5是16位,SHA是20位)

void reset()

复位

static boolean isEqual(byte[] digesta, byte[] digestb)

比效两个摘要是否相同

代码：

import java.security.*;
            public class myDigest {
            public static void main(String[] args)  {
            myDigest my=new myDigest();
            my.testDigest();
            }
            public void testDigest()
            {
            try {
            String myinfo="我的测试信息";
            //java.security.MessageDigest alg=java.security.MessageDigest.getInstance("MD5");
            java.security.MessageDigest alga=java.security.MessageDigest.getInstance("SHA-1");
            alga.update(myinfo.getBytes());
            byte[] digesta=alga.digest();
            System.out.println("本信息摘要是:"+byte2hex(digesta));
            //通过某中方式传给其他人你的信息(myinfo)和摘要(digesta) 对方可以判断是否更改或传输正常
            java.security.MessageDigest algb=java.security.MessageDigest.getInstance("SHA-1");
            algb.update(myinfo.getBytes());
            if (algb.isEqual(digesta,algb.digest())) {
            System.out.println("信息检查正常");
            }
            else
            {
            System.out.println("摘要不相同");
            }
            }
            catch (java.security.NoSuchAlgorithmException ex) {
            System.out.println("非法摘要算法");
            }
            }
            public String byte2hex(byte[] b) //二行制转字符串
            {
            String hs="";
            String stmp="";
            for (int n=0;n<b.length;n++)
            {
            stmp=(java.lang.Integer.toHexString(b[n] & 0XFF));
            if (stmp.length()==1) hs=hs+"0"+stmp;
            else hs=hs+stmp;
            if (n<b.length-1)  hs=hs+":";
            }
            return hs.toUpperCase();
            }
            }


2.3. 数字签名DSA

   1. 对于一个用户来讲首先要生成他的密钥对,并且分别保存

      生成一个KeyPairGenerator实例

         java.security.KeyPairGenerator  keygen=java.security.KeyPairGenerator.getInstance("DSA");
                          如果设定随机产生器就用如相代码初始化
                      SecureRandom secrand=new SecureRandom();
                      secrand.setSeed("tttt".getBytes()); //初始化随机产生器
                      keygen.initialize(512,secrand);     //初始化密钥生成器
                      否则
                      keygen.initialize(512);
                      生成密钥公钥pubkey和私钥prikey
                      KeyPair keys=keygen.generateKeyPair(); //生成密钥组
                      PublicKey pubkey=keys.getPublic();
                      PrivateKey prikey=keys.getPrivate();
                      分别保存在myprikey.dat和mypubkey.dat中,以便下次不在生成
                      (生成密钥对的时间比较长
                      java.io.ObjectOutputStream out=new java.io.ObjectOutputStream(new java.io.FileOutputStream("myprikey.dat"));
                           out.writeObject(prikey);
                      out.close();
                      out=new java.io.ObjectOutputStream(new java.io.FileOutputStream("mypubkey.dat"));
                           out.writeObject(pubkey);
                      out.close();
                     



   2. 用他私人密钥(prikey)对他所确认的信息(info)进行数字签名产生一个签名数组

      从文件中读入私人密钥(prikey)

         java.io.ObjectInputStream in=new java.io.ObjectInputStream(new java.io.FileInputStream("myprikey.dat"));
                          PrivateKey myprikey=(PrivateKey)in.readObject();
                      in.close();
                      初始一个Signature对象,并用私钥对信息签名
                      java.security.Signature signet=java.security.Signature.getInstance("DSA");
                      signet.initSign(myprikey);
                      signet.update(myinfo.getBytes());
                      byte[] signed=signet.sign();
                      把信息和签名保存在一个文件中(myinfo.dat)
                      java.io.ObjectOutputStream out=new java.io.ObjectOutputStream(new java.io.FileOutputStream("myinfo.dat"));
                            out.writeObject(myinfo);
                      out.writeObject(signed);
                      out.close();
                      把他的公钥的信息及签名发给其它用户
                     



   3. 其他用户用他的公共密钥(pubkey)和签名(signed)和信息(info)进行验证是否由他签名的信息

      读入公钥
      java.io.ObjectInputStream in=new java.io.ObjectInputStream(new java.io.FileInputStream("mypubkey.dat"));
      PublicKey pubkey=(PublicKey)in.readObject();
      in.close();

      读入签名和信息
      in=new java.io.ObjectInputStream(new java.io.FileInputStream("myinfo.dat"));
      String info=(String)in.readObject();
      byte[] signed=(byte[])in.readObject();
      in.close();

      初始一个Signature对象,并用公钥和签名进行验证
      java.security.Signature signetcheck=java.security.Signature.getInstance("DSA");
      signetcheck.initVerify(pubkey);
      signetcheck.update(info.getBytes());
      if (signetcheck.verify(signed)) { System.out.println("签名正常");}

      对于密钥的保存本文是用对象流的方式保存和传送的,也可可以用编码的方式保存.注意要
      import java.security.spec.*
      import java.security.*

      具休说明如下
          * public key是用X.509编码的,例码如下:

              byte[] bobEncodedPubKey=mypublic.getEncoded(); //生成编码
                                //传送二进制编码
                                //以下代码转换编码为相应key对象
                                X509EncodedKeySpec bobPubKeySpec = new X509EncodedKeySpec(bobEncodedPubKey);
                                KeyFactory keyFactory = KeyFactory.getInstance("DSA");
                                PublicKey bobPubKey = keyFactory.generatePublic(bobPubKeySpec);
                               



          * 对于Private key是用PKCS#8编码,例码如下:

             byte[] bPKCS=myprikey.getEncoded();
                                //传送二进制编码
                                //以下代码转换编码为相应key对象
                                PKCS8EncodedKeySpec priPKCS8=new PKCS8EncodedKeySpec(bPKCS);
                                KeyFactory keyf=KeyFactory.getInstance("DSA");
                                PrivateKey otherprikey=keyf.generatePrivate(priPKCS8);
                               



   4. 常用API

      java.security.KeyPairGenerator 密钥生成器类
      public static KeyPairGenerator getInstance(String algorithm) throws NoSuchAlgorithmException
      以指定的算法返回一个KeyPairGenerator 对象
      参数: algorithm 算法名.如:"DSA","RSA"

      public void initialize(int keysize)

      以指定的长度初始化KeyPairGenerator对象,如果没有初始化系统以1024长度默认设置

      参数:keysize 算法位长.其范围必须在 512 到 1024 之间，且必须为 64 的倍数

      public void initialize(int keysize, SecureRandom random)
      以指定的长度初始化和随机发生器初始化KeyPairGenerator对象
      参数:keysize 算法位长.其范围必须在 512 到 1024 之间，且必须为 64 的倍数
      random 一个随机位的来源(对于initialize(int keysize)使用了默认随机器

      public abstract KeyPair generateKeyPair()
      产生新密钥对

      java.security.KeyPair 密钥对类
      public PrivateKey getPrivate()
      返回私钥

      public PublicKey getPublic()
      返回公钥

      java.security.Signature 签名类
      public static Signature getInstance(String algorithm) throws NoSuchAlgorithmException
      返回一个指定算法的Signature对象
      参数 algorithm 如:"DSA"

      public final void initSign(PrivateKey privateKey)
      throws InvalidKeyException
      用指定的私钥初始化
      参数:privateKey 所进行签名时用的私钥

      public final void update(byte data)
      throws SignatureException
      public final void update(byte[] data)
      throws SignatureException
      public final void update(byte[] data, int off, int len)
      throws SignatureException
      添加要签名的信息

      public final byte[] sign()
      throws SignatureException
      返回签名的数组,前提是initSign和update

      public final void initVerify(PublicKey publicKey)
      throws InvalidKeyException
      用指定的公钥初始化
      参数:publicKey 验证时用的公钥

      public final boolean verify(byte[] signature)
      throws SignatureException
      验证签名是否有效,前提是已经initVerify初始化
      参数: signature 签名数组

       */
                      import java.security.*;
                      import java.security.spec.*;
                      public class testdsa {
                      public static void main(String[] args) throws java.security.NoSuchAlgorithmException,java.lang.Exception {
                              testdsa my=new testdsa();
                      my.run();
                      }
                      public void run()
                      {
                      //数字签名生成密钥
                      //第一步生成密钥对,如果已经生成过,本过程就可以跳过,对用户来讲myprikey.dat要保存在本地
                      //而mypubkey.dat给发布给其它用户
                      if ((new java.io.File("myprikey.dat")).exists()==false) {
                      if (generatekey()==false) {
                      System.out.println("生成密钥对败");
                      return;
                      };
                      }
                      //第二步,此用户
                      //从文件中读入私钥,对一个字符串进行签名后保存在一个文件(myinfo.dat)中
                      //并且再把myinfo.dat发送出去
                      //为了方便数字签名也放进了myifno.dat文件中,当然也可分别发送
                      try {
                      java.io.ObjectInputStream in=new java.io.ObjectInputStream(new java.io.FileInputStream("myprikey.dat"));
                        PrivateKey myprikey=(PrivateKey)in.readObject();
                      in.close();
                      // java.security.spec.X509EncodedKeySpec pubX509=new java.security.spec.X509EncodedKeySpec(bX509);
                       //java.security.spec.X509EncodedKeySpec pubkeyEncode=java.security.spec.X509EncodedKeySpec
                        String myinfo="这是我的信息";    //要签名的信息
                      //用私钥对信息生成数字签名
                      java.security.Signature signet=java.security.Signature.getInstance("DSA");
                      signet.initSign(myprikey);
                      signet.update(myinfo.getBytes());
                      byte[] signed=signet.sign();  //对信息的数字签名
                      System.out.println("signed(签名内容)="+byte2hex(signed));
                      //把信息和数字签名保存在一个文件中
                      java.io.ObjectOutputStream out=new java.io.ObjectOutputStream(new java.io.FileOutputStream("myinfo.dat"));
                        out.writeObject(myinfo);
                      out.writeObject(signed);
                      out.close();
                      System.out.println("签名并生成文件成功");
                      }
                      catch (java.lang.Exception e) {
                      e.printStackTrace();
                      System.out.println("签名并生成文件失败");
                      };
                      //第三步
                      //其他人通过公共方式得到此户的公钥和文件
                      //其他人用此户的公钥,对文件进行检查,如果成功说明是此用户发布的信息.
                      //
                      try {
                      java.io.ObjectInputStream in=new java.io.ObjectInputStream(new java.io.FileInputStream("mypubkey.dat"));
                         PublicKey pubkey=(PublicKey)in.readObject();
                      in.close();
                      System.out.println(pubkey.getFormat());
                      in=new java.io.ObjectInputStream(new java.io.FileInputStream("myinfo.dat"));
                      String info=(String)in.readObject();
                      byte[] signed=(byte[])in.readObject();
                      in.close();
                      java.security.Signature signetcheck=java.security.Signature.getInstance("DSA");
                      signetcheck.initVerify(pubkey);
                      signetcheck.update(info.getBytes());
                      if (signetcheck.verify(signed)) {
                      System.out.println("info="+info);
                      System.out.println("签名正常");
                      }
                      else  System.out.println("非签名正常");
                      }
                      catch (java.lang.Exception e) {e.printStackTrace();};
                      }
                      //生成一对文件myprikey.dat和mypubkey.dat---私钥和公钥,
                      //公钥要用户发送(文件,网络等方法)给其它用户,私钥保存在本地
                      public boolean generatekey()
                      {
                      try {
                      java.security.KeyPairGenerator  keygen=java.security.KeyPairGenerator.getInstance("DSA");
                       // SecureRandom secrand=new SecureRandom();
                      // secrand.setSeed("tttt".getBytes()); //初始化随机产生器
                      // keygen.initialize(576,secrand);     //初始化密钥生成器
                      keygen.initialize(512);
                      KeyPair keys=keygen.genKeyPair();
                      //  KeyPair keys=keygen.generateKeyPair(); //生成密钥组
                      PublicKey pubkey=keys.getPublic();
                      PrivateKey prikey=keys.getPrivate();
                      java.io.ObjectOutputStream out=new java.io.ObjectOutputStream(new java.io.FileOutputStream("myprikey.dat"));
                        out.writeObject(prikey);
                      out.close();
                      System.out.println("写入对象 prikeys ok");
                      out=new java.io.ObjectOutputStream(new java.io.FileOutputStream("mypubkey.dat"));
                      out.writeObject(pubkey);
                      out.close();
                      System.out.println("写入对象 pubkeys ok");
                      System.out.println("生成密钥对成功");
                      return true;
                      }
                      catch (java.lang.Exception e) {
                      e.printStackTrace();
                      System.out.println("生成密钥对失败");
                      return false;
                      };
                      }
                      public String byte2hex(byte[] b)
                      {
                      String hs="";
                      String stmp="";
                      for (int n=0;n<b.length;n++)
                      {
                      stmp=(java.lang.Integer.toHexString(b[n] & 0XFF));
                      if (stmp.length()==1) hs=hs+"0"+stmp;
                      else hs=hs+stmp;
                      if (n<b.length-1)  hs=hs+":";
                      }
                      return hs.toUpperCase();
                      }
                      }



2.4. DESede/DES对称算法

首先生成密钥,并保存(这里并没的保存的代码,可参考DSA中的方法)

KeyGenerator keygen = KeyGenerator.getInstance(Algorithm);

SecretKey deskey = keygen.generateKey();

用密钥加密明文(myinfo),生成密文(cipherByte)

Cipher c1 = Cipher.getInstance(Algorithm);

c1.init(Cipher.ENCRYPT_MODE,deskey);

byte[] cipherByte=c1.doFinal(myinfo.getBytes());

传送密文和密钥,本文没有相应代码可参考DSA

.............

用密钥解密密文

c1 = Cipher.getInstance(Algorithm);

c1.init(Cipher.DECRYPT_MODE,deskey);

byte[] clearByte=c1.doFinal(cipherByte);

相对来说对称密钥的使用是很简单的,对于JCE来讲支技DES,DESede,Blowfish三种加密术

对于密钥的保存各传送可使用对象流或者用二进制编码,相关参考代码如下

   SecretKey deskey = keygen.generateKey();
            byte[] desEncode=deskey.getEncoded();
            javax.crypto.spec.SecretKeySpec destmp=new javax.crypto.spec.SecretKeySpec(desEncode,Algorithm);
               SecretKey mydeskey=destmp;


相关API

KeyGenerator 在DSA中已经说明,在添加JCE后在instance进可以如下参数

DES,DESede,Blowfish,HmacMD5,HmacSHA1

javax.crypto.Cipher 加/解密器

public static final Cipher getInstance(java.lang.String transformation)
            throws java.security.NoSuchAlgorithmException,
            NoSuchPaddingException


返回一个指定方法的Cipher对象

参数:transformation 方法名(可用 DES,DESede,Blowfish)

public final void init(int opmode, java.security.Key key)
throws java.security.InvalidKeyException

用指定的密钥和模式初始化Cipher对象

参数:opmode 方式(ENCRYPT_MODE, DECRYPT_MODE, WRAP_MODE,UNWRAP_MODE)

key 密钥

public final byte[] doFinal(byte[] input)
            throws java.lang.IllegalStateException,
            IllegalBlockSizeException,
            BadPaddingException
           


对input内的串,进行编码处理,返回处理后二进制串,是返回解密文还是加解文由init时的opmode决定

注意:本方法的执行前如果有update,是对updat和本次input全部处理,否则是本inout的内容

/*
            安全程序 DESede/DES测试
            */
            import java.security.*;
            import javax.crypto.*;
            public class testdes {
            public static void main(String[] args){
            testdes my=new testdes();
            my.run();
            }
            public  void run() {
            //添加新安全算法,如果用JCE就要把它添加进去
            Security.addProvider(new com.sun.crypto.provider.SunJCE());
            String Algorithm="DES"; //定义 加密算法,可用 DES,DESede,Blowfish
            String myinfo="要加密的信息";
            try {
            //生成密钥
            KeyGenerator keygen = KeyGenerator.getInstance(Algorithm);
            SecretKey deskey = keygen.generateKey();
            //加密
            System.out.println("加密前的二进串:"+byte2hex(myinfo.getBytes()));
            System.out.println("加密前的信息:"+myinfo);
            Cipher c1 = Cipher.getInstance(Algorithm);
            c1.init(Cipher.ENCRYPT_MODE,deskey);
            byte[] cipherByte=c1.doFinal(myinfo.getBytes());
            System.out.println("加密后的二进串:"+byte2hex(cipherByte));
            //解密
            c1 = Cipher.getInstance(Algorithm);
            c1.init(Cipher.DECRYPT_MODE,deskey);
            byte[] clearByte=c1.doFinal(cipherByte);
            System.out.println("解密后的二进串:"+byte2hex(clearByte));
            System.out.println("解密后的信息:"+(new String(clearByte)));
            }
            catch (java.security.NoSuchAlgorithmException e1) {e1.printStackTrace();}
            catch (javax.crypto.NoSuchPaddingException e2) {e2.printStackTrace();}
            catch (java.lang.Exception e3) {e3.printStackTrace();}
            }
            public String byte2hex(byte[] b) //二行制转字符串
            {
            String hs="";
            String stmp="";
            for (int n=0;n<b.length;n++)
            {
            stmp=(java.lang.Integer.toHexString(b[n] & 0XFF));
            if (stmp.length()==1) hs=hs+"0"+stmp;
            else hs=hs+stmp;
            if (n<b.length-1)  hs=hs+":";
            }
            return hs.toUpperCase();
            }
            }



2.5. Diffie-Hellman密钥一致协议

公开密钥密码体制的奠基人Diffie和Hellman所提出的 "指数密钥一致协议"(Exponential Key Agreement Protocol),该协议不要求别的安全性先决条件,允许两名用户在公开媒体上交换信息以生成"一致"的,可以共享的密钥。在JCE的中实现用户 alice生成DH类型的密钥对,如果长度用1024生成的时间请,推荐第一次生成后保存DHParameterSpec,以便下次使用直接初始化.使其速度加快

System.out.println("ALICE: 产生 DH 对 ...");
            KeyPairGenerator aliceKpairGen = KeyPairGenerator.getInstance("DH");
            aliceKpairGen.initialize(512);
            KeyPair aliceKpair = aliceKpairGen.generateKeyPair();


alice生成公钥发送组bob

byte[] alicePubKeyEnc = aliceKpair.getPublic().getEncoded();


bob从alice发送来的公钥中读出DH密钥对的初始参数生成bob的DH密钥对

注意这一步一定要做,要保证每个用户用相同的初始参数生成的

   DHParameterSpec dhParamSpec = ((DHPublicKey)alicePubKey).getParams();
            KeyPairGenerator bobKpairGen = KeyPairGenerator.getInstance("DH");
            bobKpairGen.initialize(dhParamSpec);
            KeyPair bobKpair = bobKpairGen.generateKeyPair();


bob根据alice的公钥生成本地的DES密钥

   KeyAgreement bobKeyAgree = KeyAgreement.getInstance("DH");
            bobKeyAgree.init(bobKpair.getPrivate());
            bobKeyAgree.doPhase(alicePubKey, true);
            SecretKey bobDesKey = bobKeyAgree.generateSecret("DES");


bob已经生成了他的DES密钥,他现把他的公钥发给alice,

      byte[] bobPubKeyEnc = bobKpair.getPublic().getEncoded();


alice根据bob的公钥生成本地的DES密钥

       ,,,,,,解码
            KeyAgreement aliceKeyAgree = KeyAgreement.getInstance("DH");
            aliceKeyAgree.init(aliceKpair.getPrivate());
            aliceKeyAgree.doPhase(bobPubKey, true);
            SecretKey aliceDesKey = aliceKeyAgree.generateSecret("DES");


bob和alice能过这个过程就生成了相同的DES密钥,在这种基础就可进行安全能信

常用API

java.security.KeyPairGenerator 密钥生成器类
public static KeyPairGenerator getInstance(String algorithm)
throws NoSuchAlgorithmException
以指定的算法返回一个KeyPairGenerator 对象
参数: algorithm 算法名.如:原来是DSA,现在添加了 DiffieHellman(DH)

public void initialize(int keysize)
以指定的长度初始化KeyPairGenerator对象,如果没有初始化系统以1024长度默认设置
参数:keysize 算法位长.其范围必须在 512 到 1024 之间，且必须为 64 的倍数
注意:如果用1024生长的时间很长,最好生成一次后就保存,下次就不用生成了

public void initialize(AlgorithmParameterSpec params)
throws InvalidAlgorithmParameterException
以指定参数初始化

javax.crypto.interfaces.DHPublicKey
public DHParameterSpec getParams()
返回
java.security.KeyFactory

public static KeyFactory getInstance(String algorithm)
throws NoSuchAlgorithmException
以指定的算法返回一个KeyFactory
参数: algorithm 算法名:DSH,DH

public final PublicKey generatePublic(KeySpec keySpec)
throws InvalidKeySpecException
根据指定的key说明,返回一个PublicKey对象

java.security.spec.X509EncodedKeySpec
public X509EncodedKeySpec(byte[] encodedKey)
根据指定的二进制编码的字串生成一个key的说明
参数:encodedKey 二进制编码的字串(一般能过PublicKey.getEncoded()生成)
javax.crypto.KeyAgreement 密码一至类

public static final KeyAgreement getInstance(java.lang.String algorithm)
throws java.security.NoSuchAlgorithmException
返回一个指定算法的KeyAgreement对象
参数:algorithm 算法名,现在只能是DiffieHellman(DH)

public final void init(java.security.Key key)
throws java.security.InvalidKeyException
用指定的私钥初始化
参数:key 一个私钥

public final java.security.Key doPhase(java.security.Key key,
boolean lastPhase)
throws java.security.InvalidKeyException,
java.lang.IllegalStateException
用指定的公钥进行定位,lastPhase确定这是否是最后一个公钥,对于两个用户的
情况下就可以多次定次,最后确定
参数:key 公钥
lastPhase 是否最后公钥

public final SecretKey generateSecret(java.lang.String algorithm)
throws java.lang.IllegalStateException,
java.security.NoSuchAlgorithmException,
java.security.InvalidKeyException
根据指定的算法生成密钥
参数:algorithm 加密算法(可用 DES,DESede,Blowfish)

*/
            import java.io.*;
            import java.math.BigInteger;
            import java.security.*;
            import java.security.spec.*;
            import java.security.interfaces.*;
            import javax.crypto.*;
            import javax.crypto.spec.*;
            import javax.crypto.interfaces.*;
            import com.sun.crypto.provider.SunJCE;
            public class testDHKey {
            public static void main(String argv[]) {
            try {
            testDHKey my= new testDHKey();
            my.run();
            } catch (Exception e) {
            System.err.println(e);
            }
            }
            private void run() throws Exception {
            Security.addProvider(new com.sun.crypto.provider.SunJCE());
            System.out.println("ALICE: 产生 DH 对 ...");
            KeyPairGenerator aliceKpairGen = KeyPairGenerator.getInstance("DH");
            aliceKpairGen.initialize(512);
            KeyPair aliceKpair = aliceKpairGen.generateKeyPair(); //生成时间长
            // 张三(Alice)生成公共密钥 alicePubKeyEnc 并发送给李四(Bob) ,
            //比如用文件方式,socket.....
            byte[] alicePubKeyEnc = aliceKpair.getPublic().getEncoded();
            //bob接收到alice的编码后的公钥,将其解码
            KeyFactory bobKeyFac = KeyFactory.getInstance("DH");
            X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec  (alicePubKeyEnc);
            PublicKey alicePubKey = bobKeyFac.generatePublic(x509KeySpec);
            System.out.println("alice公钥bob解码成功");
            // bob必须用相同的参数初始化的他的DH KEY对,所以要从Alice发给他的公开密钥,
            //中读出参数,再用这个参数初始化他的 DH key对
            //从alicePubKye中取alice初始化时用的参数
            DHParameterSpec dhParamSpec = ((DHPublicKey)alicePubKey).getParams();
            KeyPairGenerator bobKpairGen = KeyPairGenerator.getInstance("DH");
            bobKpairGen.initialize(dhParamSpec);
            KeyPair bobKpair = bobKpairGen.generateKeyPair();
            System.out.println("BOB: 生成 DH key 对成功");
            KeyAgreement bobKeyAgree = KeyAgreement.getInstance("DH");
            bobKeyAgree.init(bobKpair.getPrivate());
            System.out.println("BOB: 初始化本地key成功");
            //李四(bob) 生成本地的密钥 bobDesKey
            bobKeyAgree.doPhase(alicePubKey, true);
            SecretKey bobDesKey = bobKeyAgree.generateSecret("DES");
            System.out.println("BOB: 用alice的公钥定位本地key,生成本地DES密钥成功");
            // Bob生成公共密钥 bobPubKeyEnc 并发送给Alice,
            //比如用文件方式,socket.....,使其生成本地密钥
            byte[] bobPubKeyEnc = bobKpair.getPublic().getEncoded();
            System.out.println("BOB向ALICE发送公钥");
            // alice接收到 bobPubKeyEnc后生成bobPubKey
            // 再进行定位,使aliceKeyAgree定位在bobPubKey
            KeyFactory aliceKeyFac = KeyFactory.getInstance("DH");
            x509KeySpec = new X509EncodedKeySpec(bobPubKeyEnc);
            PublicKey bobPubKey = aliceKeyFac.generatePublic(x509KeySpec);
            System.out.println("ALICE接收BOB公钥并解码成功");
            ;
            KeyAgreement aliceKeyAgree = KeyAgreement.getInstance("DH");
            aliceKeyAgree.init(aliceKpair.getPrivate());
            System.out.println("ALICE: 初始化本地key成功");
            aliceKeyAgree.doPhase(bobPubKey, true);
            // 张三(alice) 生成本地的密钥 aliceDesKey
            SecretKey aliceDesKey = aliceKeyAgree.generateSecret("DES");
            System.out.println("ALICE: 用bob的公钥定位本地key,并生成本地DES密钥");
            if (aliceDesKey.equals(bobDesKey)) System.out.println("张三和李四的密钥相同");
            //现在张三和李四的本地的deskey是相同的所以,完全可以进行发送加密,接收后解密,达到
            //安全通道的的目的
            /*
            * bob用bobDesKey密钥加密信息
            */
            Cipher bobCipher = Cipher.getInstance("DES");
            bobCipher.init(Cipher.ENCRYPT_MODE, bobDesKey);
            String bobinfo= "这是李四的机密信息";
            System.out.println("李四加密前原文:"+bobinfo);
            byte[] cleartext =bobinfo.getBytes();
            byte[] ciphertext = bobCipher.doFinal(cleartext);
            /*
            * alice用aliceDesKey密钥解密
            */
            Cipher aliceCipher = Cipher.getInstance("DES");
            aliceCipher.init(Cipher.DECRYPT_MODE, aliceDesKey);
            byte[] recovered = aliceCipher.doFinal(ciphertext);
            System.out.println("alice解密bob的信息:"+(new String(recovered)));
            if (!java.util.Arrays.equals(cleartext, recovered))
            throw new Exception("解密后与原文信息不同");
            System.out.println("解密后相同");
            }
            }