Java，如何实现移位密码(凯撒密码)

I want to implement a Caesar Cipher shift to increase each letter in a string by 3.

我想要实现一个凯撒密码转换，将每一个字母在一个字符串中增加3。

I am receiving this error:

我收到这个错误:

possible loss of precision required char; found int

Here is my code so far:

下面是我的代码:

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

public class CaesarCipher
{
    public static void main (String [] args) {

        char[] letters = {'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'};

        char[] message = "onceuponatime".toCharArray();
        char[] eMessage = new char[message.length];
        char shift = 3;

        //encrypting message
        for(int i = 0; i <= message.length; ++i)
        {
            eMessage[i] = (message[i] + shift) % (char) letters.length;
            System.out.println(x);               
        }              
    }
}

What causes this error? How can I implement a caesar Cipher shift to increase each letter in a string by 3?

导致这个错误的原因是什么?我怎样才能实现一个凯撒密码转换，将每一个字母在一个字符串中增加3?

5 个解决方案

#1

Java Shift Caesar Cipher by shift spaces.

Restrictions:

限制:

1. Only works with a positive number in the shift parameter.
2. 只在移位参数中使用正数。
3. Only works with shift less than 26.
4. 只适用于小于26的移动。
5. Does a += which will bog the computer down for bodies of text longer than a few thousand characters.
6. a +=会使计算机的正文长度超过几千个字符。
7. Does a cast number to character, so it will fail with anything but ascii letters.
8. 将一个数字转换成字符，因此它将以任何形式失败，而不是ascii字符。
9. Only tolerates letters a through z. Cannot handle spaces, numbers, symbols or unicode.
10. 只允许字母a到z。不能处理空格、数字、符号或unicode。
11. Code violates the DRY (don't repeat yourself) principle by repeating the calculation more than it has to.
12. 代码违背了DRY(不要重复自己)的原则，重复计算比它必须要多。

Pseudocode:

伪代码:

1. Loop through each character in the string.
2. 循环遍历字符串中的每个字符。
3. Add shift to the character and if it falls off the end of the alphabet then subtract shift from the number of letters in the alphabet (26)
4. 增加字符的转换，如果它从字母表的末尾掉下来，那么将字母表中的字母的数量从字母表中减去。
5. If the shift does not make the character fall off the end of the alphabet, then add the shift to the character.
6. 如果转换不能使字符从字母表的末尾下降，那么就增加字符的转换。
7. Append the character onto a new string. Return the string.
8. 将字符追加到一个新字符串中。返回字符串。

Function:

功能:

String cipher(String msg, int shift){
    String s = "";
    int len = msg.length();
    for(int x = 0; x < len; x++){
        char c = (char)(msg.charAt(x) + shift);
        if (c > 'z')
            s += (char)(msg.charAt(x) - (26-shift));
        else
            s += (char)(msg.charAt(x) + shift);
    }
    return s;
}

How to invoke it:

如何调用它:

System.out.println(cipher("abc", 3));  //prints def
System.out.println(cipher("xyz", 3));  //prints abc

#2

Below code handles upper and lower cases as well and leaves other character as it is.

下面的代码处理上和下的情况，并留下其他字符。

import java.util.Scanner;

public class CaesarCipher
{
    public static void main(String[] args)
    {
    Scanner in = new Scanner(System.in);
    int length = Integer.parseInt(in.nextLine());
    String str = in.nextLine();
    int k = Integer.parseInt(in.nextLine());

    k = k % 26;

    System.out.println(encrypt(str, length, k));

    in.close();
    }

    private static String encrypt(String str, int length, int shift)
    {
    StringBuilder strBuilder = new StringBuilder();
    char c;
    for (int i = 0; i < length; i++)
    {
        c = str.charAt(i);
        // if c is letter ONLY then shift them, else directly add it
        if (Character.isLetter(c))
        {
        c = (char) (str.charAt(i) + shift);
        // System.out.println(c);

        // checking case or range check is important, just if (c > 'z'
        // || c > 'Z')
        // will not work
        if ((Character.isLowerCase(str.charAt(i)) && c > 'z')
            || (Character.isUpperCase(str.charAt(i)) && c > 'Z'))

            c = (char) (str.charAt(i) - (26 - shift));
        }
        strBuilder.append(c);
    }
    return strBuilder.toString();
    }
}

#3

The warning is due to you attempting to add an integer (int shift = 3) to a character value. You can change the data type to char if you want to avoid that.

警告是由于您试图向一个字符值添加一个整数(int shift = 3)。如果想要避免，可以将数据类型更改为char。

A char is 16 bits, an int is 32.

一个字符是16位，一个整数是32。

char shift = 3;
// ...
eMessage[i] = (message[i] + shift) % (char)letters.length;

As an aside, you can simplify the following:

顺便提一下，你可以简化以下内容:

char[] message = {'o', 'n', 'c', 'e', 'u', 'p', 'o', 'n', 'a', 't', 'i', 'm', 'e'}; 

To:

:

char[] message = "onceuponatime".toCharArray();

#4

Two ways to implement a Caesar Cipher:

实现凯撒密码的两种方法:

Option 1: Change chars to ASCII numbers, then you can increase the value, then revert it back to the new character.

选项1:将chars更改为ASCII码，然后您可以增加该值，然后将其还原为新的字符。

Option 2: Use a Map map each letter to a digit like this.

选项2:用地图把每个字母都映射成这样的数字。

A - 0
B - 1
C - 2
etc...

With a map you don't have to re-calculate the shift every time. Then you can change to and from plaintext to encrypted by following map.

有了地图，你不需要每次都重新计算移位。然后，您可以通过以下映射更改为和从纯文本到加密。

#5

Hello...I have created a java client server application in swing for caesar cipher...I have created a new formula that can decrypt the text properly... sorry only for lower case..!

你好……我在swing中创建了一个java客户端服务器应用程序，用于凯撒密码…我已经创建了一个可以正确解密文本的新公式……抱歉，只是为了小写。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import java.net.*;
import java.util.*;
public class ceasarserver extends JFrame implements ActionListener
{
static String cs="abcdefghijklmnopqrstuvwxyz";
static JLabel l1,l2,l3,l5,l6;
JTextField t1;
JButton close,b1;
static String en;
int num=0;
JProgressBar progress;
ceasarserver()
{
super("SERVER");
JPanel p=new JPanel(new GridLayout(10,1));
l1=new JLabel("");
l2=new JLabel("");
l3=new JLabel("");
l5=new JLabel("");
l6=new JLabel("Enter the Key...");
t1=new JTextField(30);
progress = new JProgressBar(0, 20);
progress.setValue(0);
progress.setStringPainted(true);
close=new JButton("Close");
close.setMnemonic('C');
close.setPreferredSize(new Dimension(300, 25));
close.addActionListener(this);
b1=new JButton("Decrypt");
b1.setMnemonic('D');
b1.addAction
Listener(this);
p.add(l1);
p.add(l2);
p.add(l3);
p.add(l6);
p.add(t1);
p.add(b1);
p.add(progress);
p.add(l5);
p.add(close);
add(p);
setVisible(true);
pack();
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==close)
System.exit(0);
else if(e.getSource()==b1)
{
int key=Integer.parseInt(t1.getText());
String d="";
int i=0,j,k;
while(i<en.length())
{
j=cs.indexOf(en.charAt(i));
k=(j+(26-key))%26;
d=d+cs.charAt(k);
i++;
}
while (num < 21)
{
progress.setValue(num);
try {
Thread.sleep(100);
} catch (InterruptedException ex) { }
progress.setValue( num );
Rectangle progressRect = progress.getBounds();
progressRect.x=0;
progressRect.y=0;
progress.paintImmediately( progressRect );
num++;
}
l5.setText("Decrypted text: "+d);
}
}
public static void main(String args[])throws IOException
{
new ceasarserver();
String strm =new String();
ServerSocket
ss=new ServerSocket(4321);
l1.setText("Secure data transfer Server Started....");
Socket s=ss.accept();
l2.setText("Client Connected !");
while(true)
{
Scanner br1= new Scanner(s.getInputStream());
en=br1.nextLine();
l3.setText("Client:"+en);
}
}
}



import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import java.net.*;
import java.util.*;
public class ceasarclient extends JFrame
{
String cs="abcdefghijklmnopqrstuvwxyz";
static JLabel l1,l2,l3,l4,l5;
JButton b1,b2,b3;
JTextField t1,t2;
JProgressBar progress;
int num=0;
String en="";
ceasarclient(final Socket s)
{
super("CLIENT");
JPanel p=new JPanel(new GridLayout(10,1));
setSize(500,500);
t1=new JTextField(30);
b1=new JButton("Send");
b1.setMnemonic('S');
b2=new JButton("Close");
b2.setMnemonic('C');
l1=new JLabel("Welcome to Secure Data transfer!");
l2=new JLabel("Enter the word here...");
l3=new JLabel("");
l4=new JLabel("Enter the Key:");
b3=new JButton("Encrypt");
b3.setMnemonic('E');
t2=new JTextField(30);
progress = new JProgressBar(0, 20);
progress.setValue(0);
progress.setStringPainted(true);
p.add(l1);
p.add(l2);
p.add(t1);
p.add(l4);
p.add(t2);
p.add(b3);
p.add(progress);
p.add(b1);
p.add(l3);
p.add(b2);
add(p);
setVisible(true);
b1.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
try{
PrintWriter pw=new PrintWriter(s.getOutputStream(),true);
pw.println(en);
}catch(Exception ex){};
l3.setText("Encrypted Text Sent.");
}
});
b3.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
String strw=t1.getText();
int key=Integer.parseInt(t2.getText());
int i=0,j,k;
while(i<strw.length())
{
j=cs.indexOf(strw.charAt(
i));
k=(j+key)%26;
en=en+cs.charAt(k);
i++;
}
while (num < 21)
{
progress.setValue(num);
try {
Thread.sleep(100);
} catch (InterruptedException exe) { }
progress.setValue( num );
Rectangle progressRect = progress.getBounds();
progressRect.x=0;
progressRect.y=0;
progress.paintImmediately( progressRect );
num++;
}
}
});
b2.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e) 
{
System.exit(0);
}
});
pack();
}
public static void main(String args[])throws IOException
{
final Socket s =new Socket(InetAddress.getLocalHost(),4321);
new ceasarclient(s);
}
}