对称加密算法：替代算法与置换算法

1、替代算法：

已知替代变换函数f(a)=ak mod 26，且9k mod 26=15，试计算k

import java.util.Arrays;
import javax.swing.*;

public class HelloWorld {
    public static char[] letter={'a','b','c','d','e','f','g',
                                'h','i','j','k','l','m','n',
                                'o','p','q','r','s','t','u',
                                'v','w','x','y','z'};
    
    public static char[] Encryp_letter={'a','b','c','d','e','f','g',
                                        'h','i','j','k','l','m','n',
                                        'o','p','q','r','s','t','u',
                                        'v','w','x','y','z'};        
    
    //改变序列
    public  void changeletter(int k){
        for(int i=0;i<26;i++){
            int    b=(i*k)%26;
            Encryp_letter[i]=letter[b];
        }
    }
    
    //查找在序列中的位置
    public  int selectletter(char[] charArray,char lettervalue){
        int index=0;
        char a=charArray[index];
        while(a!=lettervalue){
            index++;
            a=charArray[index];
        }
        return index;
    }
    
    //加密
    public  String Encryption(String message){
        String encry_message="";
        for(int i=0;i<message.length();i++){
        char result_letter=' ';
        result_letter=message.charAt(i);
        result_letter=Encryp_letter[selectletter(letter, result_letter)];
        encry_message=encry_message+result_letter;
        }
        return encry_message;
    }
    
    //解密
    public  String Decryption(String message){
        String decray_message="";
        for(int i=0;i<message.length();i++){
            char result_letter=' ';
            result_letter=message.charAt(i);
            result_letter=letter[selectletter(Encryp_letter, result_letter)];            
            decray_message=decray_message+result_letter;
            }
        return decray_message;
    }
    
    public static void main(String[] args) {
        HelloWorld hw=new HelloWorld();
        int k=0;
        double b=0;
        while(b!=15){
            k++;
            b=(9*k)%26;            
        }
        
        hw.changeletter(k);
        
        while(true){
        String input=JOptionPane.showInputDialog("你希望进行加密(e)还是解密(d)操作？（注：退出输入q)");
        if(input.equals("加密")||input.equals("e")){
            input=JOptionPane.showInputDialog("您需要加密的单词是？");
            String output=hw.Encryption(input);
            JOptionPane.showMessageDialog(null, input+"加密后："+output);
        }else if(input.equals("解密")||input.equals("d")){
            input=JOptionPane.showInputDialog("您需要解密的单词是？");
            String output=hw.Decryption(input);
            JOptionPane.showMessageDialog(null, input+"解密后："+output);
        }else if(input.equals("q")){
            System.exit(0);
        }else{
            JOptionPane.showMessageDialog(null, "对不起，输入错误！");
        }
        }
    }

}

 得到结果:加密substitute得到eqtexwxqxy

2、  置换加密法

1）  给定置换表“86427531”，编程实现基于该表的加密运算；

2） 加密字符串“transposition”，输出密文（提示：如字符串长度不是8的倍数，则需在字符串结尾后填充空格，使得其总长度为8的倍数）；

import javax.swing.JOptionPane;

public class replacement {

    public static int[] order = { 8, 6, 4, 2, 7, 5, 3, 1 };

    public static void main(String[] args) {
        replacement rpm = new replacement();
        while (true) {
            String input = JOptionPane
                    .showInputDialog("你希望进行加密(e)还是解密(d)操作？（注：退出输入q)");
            if (input.equals("加密") || input.equals("e")) {
                input = JOptionPane.showInputDialog("您需要加密的单词是？");
                String output = rpm.Encryption(input);
                JOptionPane.showMessageDialog(null, input + "加密后：" + output);
            } else if (input.equals("解密") || input.equals("d")) {
                input = JOptionPane.showInputDialog("您需要解密的单词是？");
                String output = rpm.Decryption(input);
                JOptionPane.showMessageDialog(null, input + "解密后：" + output);
            } else if (input.equals("q")) {
                System.exit(0);
            } else {
                JOptionPane.showMessageDialog(null, "对不起，输入错误！");
            }
        }

    }

    // 加密
    public String Encryption(String message) {
        String result = "";
        while (message.length() % 8 != 0) {
            message = message + " ";
        }

        int Long = message.length() / 8;
        String[] messageArray = new String[Long];

        for (int i = 0; i < Long; i++) {
            messageArray[i] = message.substring(i * 8, i * 8 + 8);
        }

        for (int i = 1; i <= order.length; i++) {
            int index = selectletter(order, i);
            for (int j = 0; j < Long; j++) {
                result = result + messageArray[j].charAt(index);
            }
        }
        return result;
    }

    // 解密
    public String Decryption(String message) {
        String result = "";
        while (message.length() % 8 != 0) {
            message = message + " ";
        }

        int Long = message.length() / 8;
        String[] messageArray = new String[Long];

        for (int i = 0; i < Long; i++) {
            messageArray[i] = "";
            for (int j = i; j < message.length();) {
                messageArray[i] = messageArray[i] + message.charAt(j);
                j = j + Long;
            }
        }

        // 还原数组
        String[] messageResArray = new String[Long];
        for (int j = 0; j < Long; j++) {
            messageResArray[j] = "";
            for (int i = 0; i < order.length; i++) {
                messageResArray[j] = messageResArray[j]
                        + messageArray[j].charAt(order[i] - 1);
            }
        }

        for (int j = 0; j < Long; j++) {

            result = result + messageResArray[j];

        }

        return result;
    }

    // 查找在序列中的位置
    public int selectletter(int[] charArray, int lettervalue) {
        int index = 0;
        int a = charArray[index];
        while (a != lettervalue) {
            index++;
            a = charArray[index];
        }
        return index;
    }

}