2018-2019-2 20175214 实验五《网络编程与安全》实验报告

时间：2019-05-26 20:11:51 收藏：0 阅读：112

一、实验准备情况概述

结对对象：20175209王梓鸿
之前的结对项目已经完成过四则运算的内容，因此在完成实验时没有完全使用博客链接中给定的代码，基本采用之前结对项目的代码，并且结对项目中的四则运算还可以实现分数的运算，更加全面。
在完成实验的过程中需要参考实验三中Java密码学算法中的内容。

二、实验内容及步骤

1.提交1

实验要求：

结对实现中缀表达式转后缀表达式的功能 MyBC.java
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
上传测试代码运行结果截图和码云链接

实验原理
- 我们习惯使用的计算表达式称作中缀表达式，但计算机在计算时不使用中缀表达式；
- 因为中缀表达式需要计算机遇到符号后向后扫描一位若为括号或优先级更高的操作符还需要向后继续扫描；
- 而后缀表达式严格按照从左到右进行计算的模式符合计算机运行方式；
- 因此表达式求值分为两部分：中缀转后缀、后缀表达式求值。

实验代码

中缀转后缀MyBC.java

伪代码

1、设立空栈用于存放操作符
2、从左到右扫描中缀式，若遇到操作数，直接输出，并以空格作为分隔符；
3、若遇到运算符，则与栈顶元素比较，比栈顶级别高则进栈，否则退出栈顶元素并输出，并以空格作为分隔符，优先级从高到低为')' '/' (÷*) (+-) ；
4、若遇到左括号，进栈；若遇到右括号，则一直退栈输出，直到退到左括号止;
5、当栈变成空时，输出的结果即为后缀表达式。

产品代码

import java.util.Stack;
public class MyBC {
 String C = new String();
 String End = "";            //存储数字的字符串
 public void ChangeString(String str) {
 C = str;
 }
 public String ChangeOrder() {
Stack store = new Stack();     //创建一个存储字符的栈
for (int i = 0; i < C.length(); i++) {
   char op = C.charAt(i);     //将索引值为i处的字符的值返回
   if (op >= '0' && op <= '9') {
       End = End + op;
   }
   else if (op == '(') {
       store.push(op);
   }
   else if (op == '+' || op == '-' || op == '*' || op == '÷'|| op == '/') {
       End = End + " ";
       if (store.empty()) {
           store.push(op);
       }
       else if (compareValue(op) > compareValue((char) store.peek())) {     //比较运算符优先级
           store.push(op);
       }
       else {
           End = End + String.valueOf(store.pop());
           i--;
       }
   }
   else if (op == ')') {
       while ((char) store.peek() != '(') {
           End = End + " " + String.valueOf(store.pop());
       }
   store.pop();
   }
}
while (!store.empty()) {
   End = End + " " + String.valueOf(store.pop());
}
return End;
 }
 public int compareValue(char chi) {
int number = 0;
switch (chi) {
case '(':
   number = 1;
   break;
case '+':
case '-':
   number = 2;
   break;
case '*':
case '÷':
   number = 3;
   break;
case '/':
   number = 4;
   break;
case ')':
   number = 5;
   break;
default:
   number = 0;
   break;
}
return number;
 }
}

后缀表达式计算MyDC.java

伪代码

1、设置一个空栈用于存储数字元素；
2、从左到右扫描后缀表达式，遇操作数，进栈；
3、若遇运算符，则从栈顶弹出两个操作数，执行对应的运算，并将运算后的结果压栈栈；
4、重复执行直至后缀表达式扫描完毕，弹出栈中的最后一个元素即为表达式的值。

产品代码

import java.util.StringTokenizer;
import java.util.Stack;
public class MyDC {
 String q;
 Stack stack;
 public MyDC() {
stack = new Stack();
 }
 void set(String question) {   //输入后续排列的字符串
q = question;
 }
 public Rational get() {
Rational op1 = new Rational();
Rational op2 = new Rational();
Rational result = new Rational();
result.setNumerator(0);
StringTokenizer token = new StringTokenizer(q, " ");
String temp;
while (token.hasMoreTokens()) {
   temp = token.nextToken();
   if (Isop(temp) == 1) {     //遇到操作符，弹出栈顶的两个数进行运算
       op2 = (Rational) stack.pop();
       op1 = (Rational) stack.pop();//弹出最上面两个操作数
       result = cal(temp.charAt(0), op1, op2);//根据运算符进行运算
       stack.push(result);//将计算结果压栈
   }
   else {
       Rational num = new Rational();
       num.setNumerator(Integer.parseInt(temp));
       stack.push(num);//操作数入栈
   }
}
return result;
 }
 Rational cal(char op, Rational a, Rational b) {           //对栈顶弹出的两个数进行运算
Rational c = new Rational();
switch (op) {
   case '+':
       c = a.add(b);
       break;
   case '-':
       c = a.sub(b);
       break;
   case '*':
       c = a.muti(b);
       break;
   case '÷':
   case '/':
       if(b.getNumerator()==0) {
           System.out.println("生成的算式计算时出现了分母为0的情况！");
           System.exit(0);
       }
       else {
           c = a.div(b);
           break;
       }
   default:
       System.out.println("Wrong!");
}
return c;
 }
 int Isop(String op) {       //判断是不是运算符
if (op.equals("+") || op.equals("-") || op.equals("*") || op.equals("÷") || op.equals("/")) {
   return 1;
}
else {
   return 0;
}
 }
}

有理数类Rational

用于实现分数运算

public class Rational {
 int numerator = 1 ;   //分子
 int denominator = 1; //分母
 void setNumerator(int a) {  //设置分子
int c=f(Math.abs(a),denominator);  //计算最大公约数
numerator = a/c;
denominator = denominator/c;
if(numerator<0&&denominator<0) {
   numerator = -numerator;
   denominator = -denominator;
}
 }
 void setDenominator(int b) {  //设置分母
int c=f(numerator,Math.abs(b));  //计算最大公约数
numerator = numerator/c;
denominator = b/c;
if(numerator<0&&denominator<0) {
   numerator = -numerator;
   denominator = -denominator;
}
 }
 int getNumerator() {
return numerator;
 }
 int getDenominator() {
return denominator;
 }
 int f(int a,int b) { //求a和b的最大公约数
if(a==0) {
   return 1;
}
if(a<b) {
   int c=a;
   a=b;
   b=c;
}
int r=a%b;
while(r!=0) {
   a=b;
   b=r;
   r=a%b;
}
return b;
 }
 Rational add(Rational r) {  //加法运算
int a=r.getNumerator();
int b=r.getDenominator();
int newNumerator=numerator*b+denominator*a; //计算出新分子
int newDenominator=denominator*b;           //计算出新分母
Rational result=new Rational();
result.setNumerator(newNumerator);
result.setDenominator(newDenominator);
return result;
 }
 Rational sub(Rational r) {  //减法运算
int a=r.getNumerator();
int b=r.getDenominator();
int newNumerator=numerator*b-denominator*a;
int newDenominator=denominator*b;
Rational result=new Rational();
result.setNumerator(newNumerator);
result.setDenominator(newDenominator);
return result;
 }
 Rational muti(Rational r) { //乘法运算
int a=r.getNumerator();
int b=r.getDenominator();
int newNumerator=numerator*a;
int newDenominator=denominator*b;
Rational result=new Rational();
result.setNumerator(newNumerator);
result.setDenominator(newDenominator);
return result;
 }
 Rational div(Rational r)  { //除法运算
int a=r.getNumerator();
int b=r.getDenominator();
int newNumerator=numerator*b;
int newDenominator=denominator*a;
Rational result=new Rational();
if(a==0) {
   System.out.println("该算式无解");
   result.setNumerator(0);
}
else {
   result.setNumerator(newNumerator);
   result.setDenominator(newDenominator);
}
return result;
 }
}

测试代码Test

import java.util.*;
public class Test {
 public static void main(String[] args) {
String question = "";
String question1 = "";
Scanner scanner = new Scanner(System.in);
System.out.println("请输入题目：");
question = scanner.nextLine();
MyBC change = new MyBC();
change.ChangeString(question);
question1 = change.ChangeOrder();
System.out.println(question1);
MyDC getanswer = new MyDC();
getanswer.set(question1);
Rational answer = getanswer.get();
int a = answer.getNumerator();
int b = answer.getDenominator();
float result = (float)a/b;
System.out.println("结果为（保留两位小数）：");
System.out.println(String.format("%.2f",result));
 }
}

测试结果截图

技术分享图片

2.提交2

实验要求

1、基于Java Socket实现客户端/服务器功能，传输方式用TCP
2、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
3、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
4、客户端显示服务器发送过来的结果
5、上传测试结果截图和码云链接

实验原理
- 获取Client端的IP地址
  - 打开终端，输入ipconfig查看；
  - 在命令行输入IP地址；
  - 调用InetAddress类中的geetByName方法获取输入的IP地址；
- 创建一个套接字，可以使用Socket的构造方法；
  - 如：public Socket(java.lang.String host, int port) 其中，host是IP地址，port是端口号。
- 调用getInputStream()方法获得一个输入流
- 调用getOutputStream()方法获得一个输出流
- 服务器端调用ServerSocket实现套接字
- 使用accept()方法连接客户端和服务器的套接字
- 调用getInputStream()方法获得一个输入流
- 调用getOutputStream()方法获得一个输出流

实验代码

客户端Client

import java.io.*;
import java.net.*;
import java.util.Scanner;
public class Client {
 public static void main(String args[]) {
  Socket mysocket;
  DataInputStream in=null;
  DataOutputStream out=null;
  Scanner scanner = new Scanner(System.in);
  try{
      System.out.print("输入服务器的IP:");
      String IP = scanner.nextLine();
      InetAddress address=InetAddress.getByName(IP);
      mysocket = new Socket(address, 2010);
      in=new DataInputStream(mysocket.getInputStream());
      out=new DataOutputStream(mysocket.getOutputStream());
      System.out.println("请输入中缀表达式：");
      while (scanner.hasNext()) {
          String question = scanner.next();
          MyBC change = new MyBC();
          change.ChangeString(question);
          String question1 = change.ChangeOrder();
          System.out.println("后缀表达式为："+question1);
          out.writeUTF(question1);
          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);
          System.out.println("请输入中缀表达式:");
      }
  }
  catch(Exception e) {
      System.out.println("服务器已断开"+e);
  }
 }
}

服务器Server

import java.io.*;
import java.net.*;
public class Server {
 public static void main(String[] args) {
  ServerSocket serverForClient = null;
  Socket socketOnServer = null;
  DataOutputStream out = null;
  DataInputStream in = null;
  String question = "";
  try {
      serverForClient = new ServerSocket(2010);
  } catch (IOException e) {
      System.out.println(e);
  }
  System.out.println("等待客户呼叫");
  try {
      socketOnServer = serverForClient.accept();
      out = new DataOutputStream(socketOnServer.getOutputStream());
      in = new DataInputStream(socketOnServer.getInputStream());
      while(true) {
          question = in.readUTF(); // in读取信息，堵塞状态
          System.out.println("服务器收到客户传递的后缀表达式为:" + question);
          MyDC getanswer = new MyDC();
          getanswer.set(question);
          Rational answer = getanswer.get();
          int a = answer.getNumerator();
          int b = answer.getDenominator();
          float result = (float) a / b;
          System.out.println("计算出的结果为"+String.format("%.2f",result));
          out.writeUTF(String.format("%.2f",result));
          Thread.sleep(500);
      }
  } catch (Exception e) {
      System.out.println("客户已断开" + e);
  }
 }
}

测试结果截图
- 客户端
- 服务器

3.提交3

实验要求

1、基于Java Socket实现客户端/服务器功能，传输方式用TCP
2、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
3、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
4、客户端显示服务器发送过来的结果
5、上传测试结果截图和码云链接

实验原理
- 本部分主要参考Java密码学算法中“Java对称加密-DES算法”部分；
- 但是这次和结对伙伴没有通过对象序列化方式写入文件中，而是直接将密钥进行传递。

伪代码

客户端

1、获取密钥生成器KeyGenerator kg=KeyGenerator.getInstance("DESede")
2、初始化密钥生成器kg.init(168);
3、生成密钥SecretKey k=kg.generateKey( );
4、获取主要编码格式byte[ ] kb=k.getEncoded( );
5、传送密钥长度及密钥内容
6、创建密码器Cipher cp=Cipher.getInstance("DESede");
7、初始化密码器cp.init(Cipher.ENCRYPT_MODE, k);
8、获取等待加密的明文byte ptext[]=s.getBytes("UTF8");
9、执行加密byte []ptext=cp.doFinal(ctext)

服务器

1、接收密钥长度
2、接收密钥内容
3、创建密码器Cipher cp=Cipher.getInstance("DESede");
4、初始化密码器cp.init(Cipher.DECRYPT_MODE, k);
5、执行解密byte []ptext=cp.doFinal(ctext)

实验代码

客户端Client

import java.io.*;
import java.net.*;
import javax.crypto.*;
import java.util.Scanner;
public class Client {
 public static void main(String args[]) throws Exception{
  Socket mysocket;
  DataInputStream in=null;
  DataOutputStream out=null;
  Scanner scanner = new Scanner(System.in);
  try {
      System.out.print("输入服务器的IP:");
      String IP = scanner.nextLine();
      InetAddress address=InetAddress.getByName(IP);
      mysocket = new Socket(address, 2010);
      in = new DataInputStream(mysocket.getInputStream());
      out = new DataOutputStream(mysocket.getOutputStream());
      KeyGenerator kg = KeyGenerator.getInstance("DESede");
      kg.init(168);
      SecretKey k = kg.generateKey();
      byte []kb = k.getEncoded();
      out.writeUTF(kb.length+ "");
      System.out.println("产生的密钥为");
      for(int i=0;i<kb.length;i++) {
          System.out.print(kb[i]+ " ");
          out.writeUTF(kb[i] +"");
      }
      System.out.println("\n请输入中缀表达式：");
      while(scanner.hasNext()) {
          String question = scanner.next();
          MyBC change = new MyBC();
          change.ChangeString(question);
          String question1 = change.ChangeOrder();
          System.out.println("后缀表达式为："+question1);
          Cipher cp = Cipher.getInstance("DESede");
          cp.init(Cipher.ENCRYPT_MODE,k);
          byte ptext[] = question1.getBytes("UTF8");
          byte ctext[] = cp.doFinal(ptext);
          out.writeUTF(ctext.length + "");
          for(int i=0;i<ctext.length;i++) {
              out.writeUTF(ctext[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);
          System.out.println("请输入中缀表达式:");
      }
  }
  catch (IOException e) {
      System.out.println("服务器已断开"+e);
  }
 }
}

服务器Server

import java.io.*;
import java.net.*;
import javax.crypto.*;
import javax.crypto.spec.*;
public class Server {
 public static void main(String[] args) throws Exception{
  ServerSocket serverForClient = null;
  Socket socketOnServer = null;
  DataOutputStream out = null;
  DataInputStream in = null;
  try {
      serverForClient = new ServerSocket(2010);
  } catch (IOException e) {
  System.out.println(e);
  }
  System.out.println("等待客户呼叫");
  try {
      socketOnServer = serverForClient.accept();
      out = new DataOutputStream(socketOnServer.getOutputStream());
      in = new DataInputStream(socketOnServer.getInputStream());
      String keylength = in.readUTF();
      byte []kb = new byte[Integer.parseInt(keylength)];
      System.out.println("收到的密钥为：");
      for(int i = 0;i<Integer.parseInt(keylength);i++) {
          String str = in.readUTF();
          kb[i] = Byte.parseByte(str);
          System.out.print(kb[i] + " ");
      }
      while(true) {
          SecretKeySpec k = new SecretKeySpec(kb, "DESede");
          Cipher cp = Cipher.getInstance("DESede");
          cp.init(Cipher.DECRYPT_MODE, k);
          String clength = in.readUTF();
          byte ctext[] = new byte[Integer.parseInt(clength)];
          for (int i = 0;i<Integer.parseInt(clength);i++) {
              String temp = in.readUTF();
              ctext[i] = Byte.parseByte(temp);
          }
          byte[] ptext = cp.doFinal(ctext);
          String question = new String(ptext,"UTF8");
          System.out.print("\n后缀表达式为："+ question);
          MyDC getanswer = new MyDC();
          getanswer.set(question);
          Rational answer = getanswer.get();
          int a = answer.getNumerator();
          int b = answer.getDenominator();
          float result = (float) a / b;
          System.out.println("\n计算出的结果为"+String.format("%.2f",result));
          out.writeUTF(String.format("%.2f",result));
          Thread.sleep(500);
      }
  } catch (IOException e) {
      System.out.println("客户已断开" + e);
  }
 }
}

测试结果截图
- 客户端
- 服务器

4.提交4

实验要求

1、基于Java Socket实现客户端/服务器功能，传输方式用TCP
2、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
3、客户端和服务器用DH算法进行3DES或AES算法的密钥交换
4、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
5、客户端显示服务器发送过来的结果
6、上传测试结果截图和码云链接

实验原理
- 本部分主要参考Java密码学算法中“使用密钥协定创建共享密钥”部分
- 对博客中的代码进行了部分更改如下：
  - Key_DH和KeyAgree主类的参数改为由客户端和服务器传递，并修改方法名
    - public static void DH(String str1,String str2) throws Exception
    - public static void Agree(String str1,String str2)
  - 客户端和服务器分别产生自己的公钥和私钥，并用过字节数组的形式分别向另一方传递自己的公钥；
  - 客户端和服务器接受对方的公钥后利用自己的私钥创建共享密钥
  - 创建密钥协定对象KeyAgreement ka=KeyAgreement.getInstance("DH");
  - 初始化密钥协定对象ka.init(prk);
  - 执行密钥协定ka.doPhase(pbk,true);
  - 生成共享信息byte[ ] sb=ka.generateSecret();
  - 从文件中读取信息并给出共享密钥

实验代码

客户端Client

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.security.*;
import java.util.Scanner;
import java.net.*;
public class Client {
 public static void main(String[] args) {
  Socket mysocket;
  DataInputStream in=null;
  DataOutputStream out=null;
  Scanner scanner = new Scanner(System.in);
  try {
      System.out.print("输入服务器的IP:");
      String IP = scanner.nextLine();
      InetAddress address=InetAddress.getByName(IP);
      mysocket = new Socket(address, 2010);
      in = new DataInputStream(mysocket.getInputStream());
      out = new DataOutputStream(mysocket.getOutputStream());
      Key_DH.DH("Lpub.dat","Lpri.dat");
      FileInputStream my = new FileInputStream("Lpub.dat");
      ObjectInputStream mypub = new ObjectInputStream(my);
      Key kp = (Key) mypub.readObject();
      ByteArrayOutputStream DH = new ByteArrayOutputStream();
      ObjectOutputStream myDH = new ObjectOutputStream(DH);
      myDH.writeObject(kp);
      byte []pub = DH.toByteArray();
      out.writeUTF(pub.length+"");
      for(int i=0;i<pub.length;i++) {
          out.writeUTF(pub[i]+ "");
      }
      Thread.sleep(1000);
      int length = Integer.parseInt(in.readUTF());
      byte cpub[] = new byte[length];
      for(int i=0;i<length;i++) {
          String temp = in.readUTF();
          cpub[i] = Byte.parseByte(temp);
      }
      ByteArrayInputStream ckey1 = new ByteArrayInputStream(cpub);
      ObjectInputStream ckey = new ObjectInputStream(ckey1);
      Key k = (Key) ckey.readObject();
      FileOutputStream f2 = new FileOutputStream("W1pub.dat");
      ObjectOutputStream b2 = new ObjectOutputStream(f2);
      b2.writeObject(k);
      KeyAgree.Agree("W1pub.dat","Lpri.dat");
      FileInputStream f = new FileInputStream("sb.dat");
      byte[] keysb = new byte[24];
      f.read(keysb);
      System.out.println("公共密钥为：");
      for (int i = 0;i<24;i++) {
          System.out.print(keysb[i]+" ");
      }
      System.out.println("\n请输入中缀表达式：");
      while(scanner.hasNext()) {
          String question = scanner.next();
          MyBC change = new MyBC();
          change.ChangeString(question);
          String question1 = change.ChangeOrder();
          System.out.println("后缀表达式为：" + question1);
          SecretKeySpec k1 = new SecretKeySpec(keysb, "DESede");
          Cipher cp = Cipher.getInstance("DESede");
          cp.init(Cipher.ENCRYPT_MODE, k1);
          byte ptext[] = question1.getBytes("UTF8");
          byte ctext[] = cp.doFinal(ptext);
          System.out.println("加密后的后缀表达式为：");
          for (int i = 0; i < ctext.length; i++) {
              System.out.print(ctext[i] + " ");
          }
          out.writeUTF(ctext.length + "");
          for (int i = 0; i < ctext.length; i++) {
              out.writeUTF(ctext[i] + "");
          }
          String s=in.readUTF(); //in读取信息，堵塞状态
          System.out.println("\n客户收到服务器的回答:"+s);
          Thread.sleep(500);
          System.out.println("请输入中缀表达式:");
      }
  }
  catch (Exception e) {
      System.out.println(e);
  }
 }
}

服务器Server

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.security.*;
public class Server {
 public static void main(String[] args) throws Exception {
  ServerSocket serverForClient = null;
  Socket socketOnServer = null;
  DataOutputStream out = null;
  DataInputStream in = null;
  try {
      serverForClient = new ServerSocket(2010);
  } catch (IOException e) {
      System.out.println(e);
  }
  System.out.println("等待客户呼叫");
  try {
      socketOnServer = serverForClient.accept();
      out = new DataOutputStream(socketOnServer.getOutputStream());
      in = new DataInputStream(socketOnServer.getInputStream());
      Key_DH.DH("Wpub.dat","Wpri.dat");
      int length = Integer.parseInt(in.readUTF());
      byte cpub[] = new byte[length];
      for(int i=0;i<length;i++) {
          String temp = in.readUTF();
          cpub[i] = Byte.parseByte(temp);
      }
      ByteArrayInputStream ckey1 = new ByteArrayInputStream(cpub);
      ObjectInputStream ckey = new ObjectInputStream(ckey1);
      Key k1 = (Key) ckey.readObject();
      FileOutputStream f2 = new FileOutputStream("Lpub.dat");
      ObjectOutputStream b2 = new ObjectOutputStream(f2);
      b2.writeObject(k1);
      FileInputStream my = new FileInputStream("Wpub.dat");
      ObjectInputStream mypub = new ObjectInputStream(my);
      Key kp = (Key) mypub.readObject();
      ByteArrayOutputStream DH = new ByteArrayOutputStream();
      ObjectOutputStream myDH = new ObjectOutputStream(DH);
      myDH.writeObject(kp);
      byte []pub = DH.toByteArray();
      out.writeUTF(pub.length+"");
      for(int i=0;i<pub.length;i++) {
          out.writeUTF(pub[i]+ "");
      }
      KeyAgree.Agree("Lpub.dat","Wpri.dat");
      FileInputStream f = new FileInputStream("sb.dat");
      byte[] keysb = new byte[24];
      f.read(keysb);
      System.out.println("公共密钥为：");
      for (int i = 0;i<24;i++) {
          System.out.print(keysb[i]+" ");
      }
      while(true) {
          SecretKeySpec k = new SecretKeySpec(keysb, "DESede");
          Cipher cp = Cipher.getInstance("DESede");
          cp.init(Cipher.DECRYPT_MODE, k);
          String clength = in.readUTF();
          byte ctext[] = new byte[Integer.parseInt(clength)];
          for (int i = 0; i < Integer.parseInt(clength); i++) {
              String temp = in.readUTF();
              ctext[i] = Byte.parseByte(temp);
          }
          byte[] ptext = cp.doFinal(ctext);
          String question = new String(ptext, "UTF8");
          System.out.print("\n解密后的后缀表达式为：" + question);
          MyDC getanswer = new MyDC();
          getanswer.set(question);
          Rational answer = getanswer.get();
          int a = answer.getNumerator();
          int b = answer.getDenominator();
          float result = (float) a / b;
          System.out.println("\n计算出的结果为"+String.format("%.2f",result));
          out.writeUTF(String.format("%.2f",result));
          Thread.sleep(500);
      }
  }
  catch(Exception e) {
      System.out.println("客户已断开" + e);
  }
 }
}

测试结果截图
- 客户端
- 服务器

5.任务五

实验要求

1、基于Java Socket实现客户端/服务器功能，传输方式用TCP
2、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
3、客户端和服务器用DH算法进行3DES或AES算法的密钥交换
4、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
5、客户端显示服务器发送过来的结果
6、上传测试结果截图和码云链接

实验原理
- 本部分主要参考Java密码学算法中“Java摘要算法- MD5”部分；
- 主要在任务四基础上进行操作。

实验代码

客户端Client

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.net.Socket;
import java.security.*;
import java.util.Scanner;
import java.net.*;
public class Client {
 public static void main(String[] args) {
  Socket mysocket;
  DataInputStream in=null;
  DataOutputStream out=null;
  Scanner scanner = new Scanner(System.in);
  try {
      System.out.print("输入服务器的IP:");
      String IP = scanner.nextLine();
      InetAddress address=InetAddress.getByName(IP);
      mysocket = new Socket(address, 2010);
      in = new DataInputStream(mysocket.getInputStream());
      out = new DataOutputStream(mysocket.getOutputStream());
      Key_DH.DH("Lpub.dat","Lpri.dat");
      FileInputStream my = new FileInputStream("Lpub.dat");
      ObjectInputStream mypub = new ObjectInputStream(my);
      Key kp = (Key) mypub.readObject();
      ByteArrayOutputStream DH = new ByteArrayOutputStream();
      ObjectOutputStream myDH = new ObjectOutputStream(DH);
      myDH.writeObject(kp);
      byte []pub = DH.toByteArray();
      out.writeUTF(pub.length+"");
      for(int i=0;i<pub.length;i++) {
          out.writeUTF(pub[i]+ "");
      }
      Thread.sleep(1000);
      int length = Integer.parseInt(in.readUTF());
      byte cpub[] = new byte[length];
      for(int i=0;i<length;i++) {
          String temp = in.readUTF();
          cpub[i] = Byte.parseByte(temp);
      }
      ByteArrayInputStream ckey1 = new ByteArrayInputStream(cpub);
      ObjectInputStream ckey = new ObjectInputStream(ckey1);
      Key k = (Key) ckey.readObject();
      FileOutputStream f2 = new FileOutputStream("W1pub.dat");
      ObjectOutputStream b2 = new ObjectOutputStream(f2);
      b2.writeObject(k);
      KeyAgree.Agree("W1pub.dat","Lpri.dat");
      FileInputStream f = new FileInputStream("sb.dat");
      byte[] keysb = new byte[24];
      f.read(keysb);
      System.out.println("公共密钥为：");
      for (int i = 0;i<24;i++) {
          System.out.print(keysb[i]+" ");
      }
      System.out.println("\n请输入中缀表达式：");
      while(scanner.hasNext()) {
          String question = scanner.next();
          MyBC change = new MyBC();
          change.ChangeString(question);
          String question1 = change.ChangeOrder();
          System.out.println("后缀表达式为：" + question1);
          String mtoMD5 = DigestPass.MD5(question1);
          System.out.println("明文的MD5值为："+mtoMD5);
          out.writeUTF(mtoMD5);
          SecretKeySpec k1 = new SecretKeySpec(keysb, "DESede");
          Cipher cp = Cipher.getInstance("DESede");
          cp.init(Cipher.ENCRYPT_MODE, k1);
          byte ptext[] = question1.getBytes("UTF8");
          byte ctext[] = cp.doFinal(ptext);
          System.out.println("加密后的后缀表达式为：");
          for (int i = 0; i < ctext.length; i++) {
              System.out.print(ctext[i] + " ");
          }
          out.writeUTF(ctext.length + "");
          for (int i = 0; i < ctext.length; i++) {
              out.writeUTF(ctext[i] + "");
          }
          String s=in.readUTF(); //in读取信息，堵塞状态
          System.out.println("\n客户收到服务器的回答:"+s);
          Thread.sleep(500);
          System.out.println("请输入中缀表达式:");
      }
  }
  catch (Exception e) {
      System.out.println(e);
  }
 }
}

服务器Server

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.security.*;
public class Server {
 public static void main(String[] args) throws Exception {
  ServerSocket serverForClient = null;
  Socket socketOnServer = null;
  DataOutputStream out = null;
  DataInputStream in = null;
  try {
      serverForClient = new ServerSocket(2010);
  } catch (IOException e) {
      System.out.println(e);
  }
  System.out.println("等待客户呼叫");
  try {
      socketOnServer = serverForClient.accept();
      out = new DataOutputStream(socketOnServer.getOutputStream());
      in = new DataInputStream(socketOnServer.getInputStream());
      Key_DH.DH("Wpub.dat","Wpri.dat");
      int length = Integer.parseInt(in.readUTF());
      byte cpub[] = new byte[length];
      for(int i=0;i<length;i++) {
          String temp = in.readUTF();
          cpub[i] = Byte.parseByte(temp);
      }
      ByteArrayInputStream ckey1 = new ByteArrayInputStream(cpub);
      ObjectInputStream ckey = new ObjectInputStream(ckey1);
      Key k1 = (Key) ckey.readObject();
      FileOutputStream f2 = new FileOutputStream("L1pub.dat");
      ObjectOutputStream b2 = new ObjectOutputStream(f2);
      b2.writeObject(k1);
      FileInputStream my = new FileInputStream("Wpub.dat");
      ObjectInputStream mypub = new ObjectInputStream(my);
      Key kp = (Key) mypub.readObject();
      ByteArrayOutputStream DH = new ByteArrayOutputStream();
      ObjectOutputStream myDH = new ObjectOutputStream(DH);
      myDH.writeObject(kp);
      byte []pub = DH.toByteArray();
      out.writeUTF(pub.length+"");
      for(int i=0;i<pub.length;i++) {
          out.writeUTF(pub[i]+ "");
      }
      KeyAgree.Agree("L1pub.dat","Wpri.dat");
      FileInputStream f = new FileInputStream("sb.dat");
      byte[] keysb = new byte[24];
      f.read(keysb);
      System.out.println("公共密钥为：");
      for (int i = 0;i<24;i++) {
          System.out.print(keysb[i]+" ");
      }
      while(true) {
          String c = in.readUTF();
          SecretKeySpec k = new SecretKeySpec(keysb, "DESede");
          Cipher cp = Cipher.getInstance("DESede");
          cp.init(Cipher.DECRYPT_MODE, k);
          String clength = in.readUTF();
          byte ctext[] = new byte[Integer.parseInt(clength)];
          for (int i = 0; i < Integer.parseInt(clength); i++) {
              String temp = in.readUTF();
              ctext[i] = Byte.parseByte(temp);
          }
          byte[] ptext = cp.doFinal(ctext);
          String question = new String(ptext, "UTF8");
          System.out.println("\n解密后的后缀表达式为：" + question);
          String mtoMD5 = DigestPass.MD5(question);
          System.out.println("MD5的值为"+ mtoMD5);
          if(mtoMD5.equals(c)) {
              System.out.println("传递的MD5值和解密的后缀表达式的MD5值相同，可以解密！");
              MyDC getanswer = new MyDC();
              getanswer.set(question);
              Rational answer = getanswer.get();
              int a = answer.getNumerator();
              int b = answer.getDenominator();
              float result = (float) a / b;
              System.out.println("计算出的结果为"+String.format("%.2f",result));
              out.writeUTF(String.format("%.2f",result));
          }
          else {
              System.out.println("密文有误，不能解密！");
          }
          Thread.sleep(500);
      }
  }
  catch(Exception e) {
      System.out.println("客户已断开" + e);
  }
 }
}

测试结果截图
- 客户端
- 服务器

三、代码托管

码云链接
- 链接
伙伴的码云链接
- 链接

四、实验心得体会

本次实验综合了教材第十三章和Java密码学的相关内容，在和伙伴的讨论中，对于java的网络和安全方面的编程有了更好地掌握。

五、参考资料

原文：https://www.cnblogs.com/fzlzc/p/10927148.html