一、实验报告封面

课程：Java程序设计 班级：1752班 姓名：吕正宏 学号：20175213

指导教师：娄嘉鹏 实验日期：2019年5月27日

实验时间：13:45 - 21:00 实验序号：实验五

实验名称：网络编程与安全

实验要求：
1、完成实验、撰写实验报告，实验报告以博客方式发表在博客园，注意实验报告重点是运行结果，遇到的问题(工具查找，安装，使用，程序的编辑，调试，运行等)、解决办法（空洞的方法如“查网络”、“问同学”、“看书”等一律得0分）以及分析（从中可以得到什么启示，有什么收获，教训等）。

2、严禁抄袭，有该行为者实验成绩归零，并附加其他惩罚措施。

二、实验内容与步骤

（一）任务一

要求：

两人一组结对编程：

  1. 参考http://www.cnblogs.com/rocedu/p/6766748.html#SECDSA

  2. 结对实现中缀表达式转后缀表达式的功能 MyBC.java

  3. 结对实现从上面功能中获取的表达式中实现后缀表达式求值的功能,调用MyDC.java

  4. 上传测试代码运行结果截图和码云链接

实验步骤：

1.参考娄老师提供的博客[http://www.cnblogs.com/rocedu/p/6766748.html#SECDSA]中的MyDC.java，将31-40行的代码填充可得如下代码：

import java.util.StringTokenizer;
import java.util.Stack;

public class MyDC {
    /**
     * constant for addition symbol
     */
    private final char ADD = '+';
    /**
     * constant for subtraction symbol
     */
    private final char SUBTRACT = '-';
    /**
     * constant for multiplication symbol
     */
    private final char MULTIPLY = '*';
    /**
     * constant for division symbol
     */
    private final char DIVIDE = '/';
    /**
     * the stack
     */
    private Stack<Integer> stack;

    public MyDC() {
        stack = new Stack<Integer>();
    }

    public int evaluate(String expr) {
        int op1, op2, result = 0;
        String token;
        StringTokenizer tokenizer = new StringTokenizer(expr);
        while (tokenizer.hasMoreTokens()) {
            token = tokenizer.nextToken();

            //如果是运算符，调用isOperator
            if (isOperator(token)) {
                //从栈中弹出操作数2
                op2 = stack.pop();
                //从栈中弹出操作数1
                op1 = stack.pop();
                //根据运算符和两个操作数调用evalSingleOp计算result;
                result=evalSingleOp(token.charAt(0), op1, op2);
                //计算result入栈;
                stack.push(result);
            } else//如果是操作数
                //操作数入栈;
                stack.push(Integer.parseInt(token));
        }

        return result;
    }

    private boolean isOperator(String token) {
        return (token.equals("+") || token.equals("-") ||
                token.equals("*") || token.equals("/"));
    }

    private int evalSingleOp(char operation, int op1, int op2) {
        int result = 0;

        switch (operation) {
            case ADD:
                result = op1 + op2;
                break;
            case SUBTRACT:
                result = op1 - op2;
                break;
            case MULTIPLY:
                result = op1 * op2;
                break;
            case DIVIDE:
                result = op1 / op2;
        }

        return result;
    }
}

2.实验原理：

栈的一个应用是用来对四则运算表达式进行求值。

表达式Exp = S1 + OP + S2(S1 ，S2是两个操作数，OP为运算符)有三种标识方法：

  • OP + S1 + S2 为前缀表示法

  • S1 + OP + S2 为中缀表示法

  • S1 + S2 + OP 为后缀表示法

例如：Exp = a * b + (c - d / e) * f

  • 前缀式: + * a b * - c / d e f

  • 中缀式: a * b + c - d / e * f

  • 后缀式: a b * c d e / - f * +

我们可以看出：

  • 1.操作数之间的相对次序不变;

  • 2.运算符的相对次序不同;

  • 3.中缀式丢失了括弧信息，致使运算次序不确定;

  • 4.前缀式的运算规则为:连续出现的两个操作数和在它们之前且紧靠它们的运算符构成一个最小表达式;

*5.后缀式的运算规则为:运算符在式中出现的顺序恰为表达式的运算顺序;每个运算符和在它之前出现且紧靠它的两个操作数构成一个最小表达式。

3.查找资料后根据理解后得出的MyBC.java

public class MyBC {
    private Stack theStack;
    private String input;
    private String output = "";
    public MyBC(String in) {
        input = in;
        int stackSize = input.length();
        theStack = new Stack(stackSize);
    }
    public String doTrans() {
        for (int j = 0; j < input.length(); j++) {
            char ch = input.charAt(j);
            switch (ch) {
                case '+':
                case '-':
                    gotOper(ch, 1);
                    break;
                case '*':
                case '/':
                    gotOper(ch, 2);
                    break;
                case '(':
                    theStack.push(ch);
                    break;
                case ')':
                    gotParen(ch);
                    break;
                default:
                    output = output + ch;
                    break;
            }
        }
        while (!theStack.isEmpty()) {
            output = output + theStack.pop();
        }
        return output;
    }
    public void gotOper(char opThis, int prec1) {
        while (!theStack.isEmpty()) {
            char opTop = theStack.pop();
            if (opTop == '(') {
                theStack.push(opTop);
                break;
            }
            else {
                int prec2;
                if (opTop == '+' || opTop == '-')
                    prec2 = 1;
                else
                    prec2 = 2;
                if (prec2 < prec1) {
                    theStack.push(opTop);
                    break;
                }
                else
                    output = output + opTop;
            }
        }
        theStack.push(opThis);
    }
    public void gotParen(char ch){
        while (!theStack.isEmpty()) {
            char chx = theStack.pop();
            if (chx == '(')
                break;
            else
                output = output + chx;
        }
    }
    class Stack {
        private int maxSize;
        private char[] stackArray;
        private int top;
        public Stack(int max) {
            maxSize = max;
            stackArray = new char[maxSize];
            top = -1;
        }
        public void push(char j) {
            stackArray[++top] = j;
        }
        public char pop() {
            return stackArray[top--];
        }
        public char peek() {
            return stackArray[top];
        }
        public boolean isEmpty() {
            return (top == -1);
        }
    }
}

4.Calculate代码

import java.util.Scanner;
public class Caculate {
    public static void main(String[] args) {
        MyDC a = new MyDC();
        MyBC b = new MyBC();
        String str;
        int result;
        System.out.println("输入算式：");
        Scanner reader = new Scanner(System.in);
        str = reader.nextLine();
        str = b.result(str);
        result = a.evaluate(str);
        System.out.println("答案为："+result);
    }
}

5.运行截图

（二）任务二

要求：

结对编程：1人负责客户端，一人负责服务器

  1. 注意责任归宿，要会通过测试证明自己没有问题

  2. 基于Java Socket实现客户端/服务器功能，传输方式用TCP

  3. 客户端让用户输入中缀表达式，然后把中缀表达式调用MyBC.java的功能转化为后缀表达式，把后缀表达式通过网络发送给服务器

  4. 服务器接收到后缀表达式，调用MyDC.java的功能计算后缀表达式的值，把结果发送给客户端

  5. 客户端显示服务器发送过来的结果

实验步骤：

1.首先是客户端Client代码：

import java.io.*;
import java.net.*;
public class Client {
    public static void main(String args[]) {
        String [] mess ={"我是严顺尧的爸爸吗？"};
        Socket mysocket;
        DataInputStream in=null;
        DataOutputStream out=null;
        try{  mysocket=new Socket("127.0.0.1",2010);
            in=new DataInputStream(mysocket.getInputStream());
            out=new DataOutputStream(mysocket.getOutputStream());
            for(int i=0;i<mess.length;i++) {
                out.writeUTF(mess[i]);
                String  s=in.readUTF();   //in读取信息，堵塞状态
                System.out.println("客户收到服务器的回答:"+s);
                Thread.sleep(500);
            }
        }
        catch(Exception e) {
            System.out.println("服务器已断开"+e);
        }
    }
}

2.再是服务器端Server代码：

import java.io.*;
import java.net.*;
public class Server {
    public static void main(String args[]) {
        String [] answer ={"那必须是他爸爸呀！"};
        ServerSocket serverForClient=null;
        Socket socketOnServer=null;
        DataOutputStream out=null;
        DataInputStream  in=null;
        try { serverForClient = new ServerSocket(2010);
        }
        catch(IOException e1) {
            System.out.println(e1);
        }
        try{ System.out.println("等待客户呼叫");
            socketOnServer = serverForClient.accept(); //堵塞状态，除非有客户呼叫
            out=new DataOutputStream(socketOnServer.getOutputStream());
            in=new DataInputStream(socketOnServer.getInputStream());
            for(int i=0;i<answer.length;i++) {
                String s=in.readUTF(); // in读取信息，堵塞状态
                System.out.println("服务器收到客户的提问:"+s);
                out.writeUTF(answer[i]);
                Thread.sleep(500);
            }
        }
        catch(Exception e) {
            System.out.println("客户已断开"+e);
        }
    }
}

3.代码运行截图：

（三）任务三

要求：

加密结对编程：1人负责客户端，一人负责服务器

  1. 注意责任归宿，要会通过测试证明自己没有问题

  2. 基于Java Socket实现客户端/服务器功能，传输方式用TCP

  3. 客户端让用户输入中缀表达式，然后把中缀表达式调用MyBC.java的功能转化为后缀表达式，把后缀表达式用3DES或AES算法加密后通过网络把密文发送给服务器

  4. 服务器接收到后缀表达式表达式后，进行解密（和客户端协商密钥，可以用数组保存），然后调用MyDC.java的功能计算后缀表达式的值，把结果发送给客户端

  5. 客户端显示服务器发送过来的结果

实验步骤：

1.首先创造密钥：

import java.io.*;
import java.security.*;
public class Skey_kb{
    public static void main(String args[]) throws Exception{
        FileInputStream f=new FileInputStream("key1.dat");
        ObjectInputStream b=new ObjectInputStream(f);
        Key k=(Key)b.readObject( );
        byte[ ] kb=k.getEncoded( );
        FileOutputStream  f2=new FileOutputStream("keykb1.dat");
        f2.write(kb);
        // 打印密钥编码中的内容
        for(int i=0;i<kb.length;i++){
            System.out.print(kb[i]+",");
        }
    }
}

import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.io.*;
import java.security.*;

public class Skey {
    public static void main(String args[]) throws Exception {
        KeyGenerator kg = KeyGenerator.getInstance("DESede");
        kg.init(168);
        SecretKey k = kg.generateKey();
        FileOutputStream f = new FileOutputStream("key1.txt");
        ObjectOutputStream b = new ObjectOutputStream(f);
        b.writeObject(k);
    }
}

2、建立服务器server

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class Server_2 {
    public static void main(String args[]) {
        ServerSocket serverForClient = null;
        Socket socketOnServer = null;
        DataOutputStream out = null;
        DataInputStream in = null;
        try {
            serverForClient = new ServerSocket(3001);
        } catch (IOException e1) {
            System.out.println(e1);
        }
        try {
            System.out.println("等待客户呼叫");
            socketOnServer = serverForClient.accept(); //堵塞状态，除非有客户呼叫
            System.out.println("客户已连接");
            out = new DataOutputStream(socketOnServer.getOutputStream());
            in = new DataInputStream(socketOnServer.getInputStream());
            String leng = in.readUTF(); // in读取信息，堵塞状态
            byte ctext[] = new byte[Integer.parseInt(leng)];
            for (int i = 0;i<Integer.parseInt(leng);i++) {
                 String temp = in.readUTF();
                 ctext[i] = Byte.parseByte(temp);
            }
            // 获取密钥
            FileInputStream f2 = new FileInputStream("keykb1.txt");
            int num2 = f2.available();
            byte[] keykb = new byte[num2];
            f2.read(keykb);
            SecretKeySpec k = new SecretKeySpec(keykb, "DESede");
            // 解密
            Cipher cp = Cipher.getInstance("DESede");
            cp.init(Cipher.DECRYPT_MODE, k);
            byte[] ptext = cp.doFinal(ctext);
            System.out.println("后缀表达式已被解密：");
            for (int i = 0; i < ptext.length; i++) {
                System.out.print(ptext[i] + ",");
            }
            System.out.println("");
            // 显示明文
            String p = new String(ptext, "UTF8");
            System.out.println("服务器收到客户的请求:计算后缀表达式" + p);
            out.writeUTF(MyDC.jisuan(new StringBuffer(p))+"");
        } catch (Exception e) {
            System.out.println("客户已断开" + e);
        }
    }
}

3.建立client

import javax.crypto.Cipher;
import java.io.*;
import java.net.Socket;
import java.security.Key;
import java.util.Scanner;

public class Client_2 {
    public static void main(String args[]) {
        Socket mysocket;
        DataInputStream in = null;
        DataOutputStream out = null;
        Scanner scanner = new Scanner(System.in);
        String str;
        try {
            FileInputStream f = new FileInputStream("key1.txt");
            ObjectInputStream b = new ObjectInputStream(f);
            Key k = (Key) b.readObject();
            Cipher cp = Cipher.getInstance("DESede");
            cp.init(Cipher.ENCRYPT_MODE, k);
            mysocket = new Socket("192.168.1.125", 3001);
            in = new DataInputStream(mysocket.getInputStream());
            out = new DataOutputStream(mysocket.getOutputStream());
            System.out.println("已连接服务器，请输入中缀表达式：");
            str = scanner.nextLine();
            byte ptext[] = MyBC.tran(new StringBuffer(str)).toString().getBytes("UTF-8");
            byte ctext[] = cp.doFinal(ptext);
            System.out.println("后缀表达式已被加密：");
            for (int i = 0; i < ctext.length; i++) {
                System.out.print(ctext[i] + ",");
            }
            System.out.println("");
            out.writeUTF(ctext.length + "");
            for (int i = 0; i < ctext.length; i++) {
                out.writeUTF(ctext[i] + "");
                //System.out.print();
            }
            String s = in.readUTF();   //in读取信息，堵塞状态
            System.out.println("客户收到服务器的回应:" + s);
        } catch (Exception e) {
            System.out.println("服务器已断开" + e);
        }
    }
}

4.代码运行截图

（四）任务四

要求：

密钥分发结对编程：1人负责客户端，一人负责服务器

  1. 注意责任归宿，要会通过测试证明自己没有问题

  2. 基于Java Socket实现客户端/服务器功能，传输方式用TCP

  3. 客户端让用户输入中缀表达式，然后把中缀表达式调用MyBC.java的功能转化为后缀表达式，把后缀表达式用3DES或AES算法加密通过网络把密文发送给服务器

  4. 客户端和服务器用DH算法进行3DES或AES算法的密钥交换

  5. 服务器接收到后缀表达式表达式后，进行解密，然后调用MyDC.java的功能计算后缀表达式的值，把结果发送给客户端

  6. 客户端显示服务器发送过来的结果

实验步骤：

1.建立dh算法代码：

import java.io.*;
import java.math.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import javax.crypto.interfaces.*;

public class Key_DH{
    private static final byte skip1024ModulusBytes[] = {
            (byte)0xF4, (byte)0x88, (byte)0xFD, (byte)0x58,
            (byte)0x4E, (byte)0x49, (byte)0xDB, (byte)0xCD,
            (byte)0x20, (byte)0xB4, (byte)0x9D, (byte)0xE4,
            (byte)0x91, (byte)0x07, (byte)0x36, (byte)0x6B,
            (byte)0x33, (byte)0x6C, (byte)0x38, (byte)0x0D,
            (byte)0x45, (byte)0x1D, (byte)0x0F, (byte)0x7C,
            (byte)0x88, (byte)0xB3, (byte)0x1C, (byte)0x7C,
            (byte)0x5B, (byte)0x2D, (byte)0x8E, (byte)0xF6,
            (byte)0xF3, (byte)0xC9, (byte)0x23, (byte)0xC0,
            (byte)0x43, (byte)0xF0, (byte)0xA5, (byte)0x5B,
            (byte)0x18, (byte)0x8D, (byte)0x8E, (byte)0xBB,
            (byte)0x55, (byte)0x8C, (byte)0xB8, (byte)0x5D,
            (byte)0x38, (byte)0xD3, (byte)0x34, (byte)0xFD,
            (byte)0x7C, (byte)0x17, (byte)0x57, (byte)0x43,
            (byte)0xA3, (byte)0x1D, (byte)0x18, (byte)0x6C,
            (byte)0xDE, (byte)0x33, (byte)0x21, (byte)0x2C,
            (byte)0xB5, (byte)0x2A, (byte)0xFF, (byte)0x3C,
            (byte)0xE1, (byte)0xB1, (byte)0x29, (byte)0x40,
            (byte)0x18, (byte)0x11, (byte)0x8D, (byte)0x7C,
            (byte)0x84, (byte)0xA7, (byte)0x0A, (byte)0x72,
            (byte)0xD6, (byte)0x86, (byte)0xC4, (byte)0x03,
            (byte)0x19, (byte)0xC8, (byte)0x07, (byte)0x29,
            (byte)0x7A, (byte)0xCA, (byte)0x95, (byte)0x0C,
            (byte)0xD9, (byte)0x96, (byte)0x9F, (byte)0xAB,
            (byte)0xD0, (byte)0x0A, (byte)0x50, (byte)0x9B,
            (byte)0x02, (byte)0x46, (byte)0xD3, (byte)0x08,
            (byte)0x3D, (byte)0x66, (byte)0xA4, (byte)0x5D,
            (byte)0x41, (byte)0x9F, (byte)0x9C, (byte)0x7C,
            (byte)0xBD, (byte)0x89, (byte)0x4B, (byte)0x22,
            (byte)0x19, (byte)0x26, (byte)0xBA, (byte)0xAB,
            (byte)0xA2, (byte)0x5E, (byte)0xC3, (byte)0x55,
            (byte)0xE9, (byte)0x2F, (byte)0x78, (byte)0xC7
    };
    private static final BigInteger skip1024Modulus = new BigInteger(1, skip1024ModulusBytes);
    private static final BigInteger skip1024Base = BigInteger.valueOf(2);
    public static void fun(String s1,String s2) throws Exception{
        DHParameterSpec DHP= new DHParameterSpec(skip1024Modulus,skip1024Base);
        KeyPairGenerator kpg= KeyPairGenerator.getInstance("DH");
        kpg.initialize(DHP);
        KeyPair kp=kpg.genKeyPair();
        PublicKey pbk=kp.getPublic();
        PrivateKey prk=kp.getPrivate();
        FileOutputStream  f1=new FileOutputStream(s1);
        ObjectOutputStream b1=new  ObjectOutputStream(f1);
        b1.writeObject(pbk);        FileOutputStream  f2=new FileOutputStream(s2);
        ObjectOutputStream b2=new  ObjectOutputStream(f2);
        b2.writeObject(prk);
    }
}

2.建立KeyAgree.java

import java.io.*;
import java.math.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import javax.crypto.interfaces.*;

public class KeyAgree{
    public static void fun(String s1,String s2) throws Exception{
        // 读取对方的DH公钥
        FileInputStream f1=new FileInputStream(s1);
        ObjectInputStream b1=new ObjectInputStream(f1);
        PublicKey  pbk=(PublicKey)b1.readObject( );
//读取自己的DH私钥
        FileInputStream f2=new FileInputStream(s2);
        ObjectInputStream b2=new ObjectInputStream(f2);
        PrivateKey  prk=(PrivateKey)b2.readObject( );
        // 执行密钥协定
        KeyAgreement ka=KeyAgreement.getInstance("DH");
        ka.init(prk);
        ka.doPhase(pbk,true);
        //生成共享信息
        byte[ ] sb=ka.generateSecret();
        FileOutputStream fsb = new FileOutputStream("sb.txt");
        fsb.write(sb);
    }
}

3.建立server

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.security.Key;
import java.util.Optional;

public class Server_3 {
    public static void main(String args[]) {
        ServerSocket serverForClient = null;
        Socket socketOnServer = null;
        DataOutputStream out = null;
        DataInputStream in = null;
        try {
            serverForClient = new ServerSocket(3001);
        } catch (IOException e1) {
            System.out.println(e1);
        }
        try {
            System.out.println("等待客户呼叫");
            socketOnServer = serverForClient.accept(); //堵塞状态，除非有客户呼叫
            System.out.println("客户已连接");
            out = new DataOutputStream(socketOnServer.getOutputStream());
            in = new DataInputStream(socketOnServer.getInputStream());

            Key_DH.fun("Spub.txt","Spri.txt");
            int len = Integer.parseInt(in.readUTF());
            byte np[] = new byte[len];
            for (int i = 0;i<len;i++) {
                String temp = in.readUTF();
                np[i] = Byte.parseByte(temp);
            }
            ObjectInputStream ois = new ObjectInputStream (new ByteArrayInputStream (np));
            Key k2 = (Key)ois.readObject();;
            FileOutputStream f2 = new FileOutputStream("Cpub.txt");
            ObjectOutputStream b2 = new ObjectOutputStream(f2);
            b2.writeObject(k2);

            FileInputStream fp = new FileInputStream("Spub.txt");
            ObjectInputStream bp = new ObjectInputStream(fp);
            Key kp = (Key) bp.readObject();
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(baos);
            oos.writeObject(kp);
            byte[] kb = baos.toByteArray();
            out.writeUTF(kb.length + "");
            for (int i = 0; i < kb.length; i++) {
                out.writeUTF(kb[i] + "");
            }

            KeyAgree.fun("Cpub.txt","Spri.txt");

            String leng = in.readUTF(); // in读取信息，堵塞状态
            byte ctext[] = new byte[Integer.parseInt(leng)];
            for (int i = 0;i<Integer.parseInt(leng);i++) {
                String temp = in.readUTF();
                ctext[i] = Byte.parseByte(temp);
            }
            // 获取密钥
            FileInputStream f = new FileInputStream("sb.txt");
            byte[] keysb = new byte[24];
            f.read(keysb);
            System.out.println("公共密钥：");
            for (int i = 0;i<24;i++) {
                System.out.print(keysb[i]+",");
            }
            System.out.println("");
            SecretKeySpec k = new SecretKeySpec(keysb, "DESede");
            // 解密
            Cipher cp = Cipher.getInstance("DESede");
            cp.init(Cipher.DECRYPT_MODE, k);
            byte[] ptext = cp.doFinal(ctext);
            System.out.println("后缀表达式已被解密：");
            for (int i = 0; i < ptext.length; i++) {
                System.out.print(ptext[i] + ",");
            }
            System.out.println("");
            // 显示明文
            String p = new String(ptext, "UTF8");
            System.out.println("服务器收到客户的请求:计算后缀表达式" + p);
            out.writeUTF(MyDC.jisuan(new StringBuffer(p))+"");
        } catch (Exception e) {
            System.out.println("客户已断开" + e);
        }
    }
}

4.代码运行结果

（五）任务五

要求：

完整性校验结对编程：1人负责客户端，一人负责服务器

  1. 注意责任归宿，要会通过测试证明自己没有问题

  2. 基于Java Socket实现客户端/服务器功能，传输方式用TCP

  3. 客户端让用户输入中缀表达式，然后把中缀表达式调用MyBC.java的功能转化为后缀表达式，把后缀表达式用3DES或AES算法加密通过网络把密文和明文的MD5値发送给服务器

  4. 客户端和服务器用DH算法进行3DES或AES算法的密钥交换

  5. 服务器接收到后缀表达式表达式后，进行解密，解密后计算明文的MD5值，和客户端传来的MD5进行比较，一致则调用MyDC.java的功能计算后缀表达式的值，把结果发送给客户端

  6. 客户端显示服务器发送过来的结果

实验步骤：

1.DigestPass代码：

import java.security.*;
public class DigestPass{
    static String MD5(String str) throws Exception{
        MessageDigest m=MessageDigest.getInstance("MD5");
        m.update(str.getBytes("UTF8"));
        byte s[ ]=m.digest( );
        String result="";
        for (int i=0; i<s.length; i++){
            result+=Integer.toHexString((0x000000ff & s[i]) |
                    0xffffff00).substring(6);
        }
        return result;
    }
}

2.ServerThree代码（服务器端）：

import java.io.*;
import java.net.*;
public class ServerThree {
    public static void main(String args[]) throws  IOException{
        String sharekey="";
        int n=-1;
        byte [] a=new byte[128];
        try{  File f=new File("Sharekey.dat");
            InputStream in = new FileInputStream(f);
            while((n=in.read(a,0,100))!=-1) {
                sharekey=sharekey+new String (a,0,n);
            }
            in.close();
        }
        catch(IOException e) {
            System.out.println("File read Error"+e);
        }

        ServerSocket serverForClient=null;
        Socket socketOnServer=null;
        DataOutputStream out=null;
        DataInputStream  in=null;
        try { serverForClient = new ServerSocket(2010);
        }
        catch(IOException e1) {
            System.out.println(e1);
        }
        try{ System.out.println("等待客户呼叫");
            socketOnServer = serverForClient.accept(); //堵塞状态，除非有客户呼叫
            out=new DataOutputStream(socketOnServer.getOutputStream());
            in=new DataInputStream(socketOnServer.getInputStream());
            String keyone =in.readUTF();//读取被DH算法加密的密钥
            String truekey = Encoder.AESDncode(sharekey,keyone);//使用共享密钥对被加密的原密钥解密。
            String secret =in.readUTF(); // in读取信息，堵塞状态
            System.out.println("服务器收到的信息:"+secret);
            String mdClient=in.readUTF();
            System.out.println("客户端提供的MD5为:"+ mdClient);
            String clear = Encoder.AESDncode(truekey,secret);//使用原密钥解密表达式
            MyDC d=new MyDC();
            int answer=d.evaluate(clear);
            if((mdClient.equals(DigestPass.MD5(clear)))==true) {//判断MD5值是否相等，若相等，则返回答案
                System.out.println("MD5值匹配");
                System.out.println("服务器提供的解密:" + clear);
                System.out.println("服务器解出密文的MD5为:" + DigestPass.MD5(clear));
                out.writeUTF(answer + "");
            }
            Thread.sleep(500);
        }
        catch(Exception e) {
            System.out.println("客户已断开"+e);
        }
    }
}

3.ClientThree代码（客户端）：

import java.io.*;
import java.net.*;
import java.util.Scanner;

public class ClientThree {
    public static void main(String args[]) throws Exception {
        String key1="";
        int n1=-1;
        byte [] a1=new byte[128];
        try{  File f=new File("key1.dat");
            InputStream in = new FileInputStream(f);
            while((n1=in.read(a1,0,100))!=-1) {
                key1=key1+new String (a1,0,n1);
            }
            in.close();
        }
        catch(IOException e) {
            System.out.println("File read Error"+e);
        }
        String sharekey="";
        int n=-1;
        byte [] a=new byte[128];
        try{  File f=new File("Sharekey.dat");
            InputStream in = new FileInputStream(f);
            while((n=in.read(a,0,100))!=-1) {
                sharekey=sharekey+new String (a,0,n);
            }
            in.close();
        }
        catch(IOException e) {
            System.out.println("File read Error"+e);
        }
        Socket mysocket;
        DataInputStream in=null;
        DataOutputStream out=null;
        System.out.println("请输入算式：");
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();//输入算式
        MyBC b=new MyBC();
        str=b.result(str);
        String secret=Encoder.AESEncode(key1, str);//客户端对表达式进行加密
        String md=DigestPass.MD5(str);//客户端提供的MD5
        key1 = Encoder.AESEncode(sharekey,key1);//客户端对密钥进行DH加密
        try{  mysocket=new Socket("127.1.0.0",2010);
            in=new DataInputStream(mysocket.getInputStream());
            out=new DataOutputStream(mysocket.getOutputStream());
            out.writeUTF(key1);
            out.writeUTF(secret);
            out.writeUTF(md);
            String  s=in.readUTF();   //in读取信息，堵塞状态
            System.out.println("客户收到服务器的回答:"+s);
            Thread.sleep(50000);
        }
        catch(Exception e) {
            System.out.println("服务器已断开"+e);
        }
    }
}

4.实验截图：

实验感想

通过这次实验，对java和密码学知识有了更好的认识，也对密码学中类似AES、DES的各种算法有了更深一步的学习。