对称加密算法：替代算法与置换算法

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）；
View Code
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;
}
}。