java caesar密码 [英] java caesar cipher code

问题描述

这是我的代码

  public class CaesarCipher 
 {
 public static final String ALPHABET =abcdefghijklmnopqrstuvwxyz; 
 
 public static String encrypt（String plainText，int shiftKey）
 {
 plainText = plainText.toLowerCase（）; 
 String cipherText =; （int i = 0; i< plainText.length（）; i ++）
 {
 int charPosition = ALPHABET.indexOf（plainText.charAt（i））; 
 
 int keyVal =（shiftKey + charPosition）％26; 
 char replaceVal = ALPHABET.charAt（keyVal）; 
 cipherText + = replaceVal; 
} 
 return cipherText; 
} 
 
 public static String decrypt（String cipherText，int shiftKey）
 {
 cipherText = cipherText.toLowerCase（）; 
 String plainText =; （int i = 0; i< cipherText.length（）; i ++）
 {
 int charPosition = ALPHABET.indexOf（cipherText.charAt（i））; 
 
 int keyVal =（charPosition  -  shiftKey）％26; 
 if（keyVal< 0）
 {
 keyVal = ALPHABET.length（）+ keyVal; 
} 
 char replaceVal = ALPHABET.charAt（keyVal）; 
 plainText + = replaceVal; 
} 
返回plainText; 
} 
 
 public static void main（String [] args）
 {
扫描仪sc =新扫描仪（System.in）; 
 System.out.println（输入加密字符串）; 
 String message = new String（）; 
 message = sc.next（）; 
 System.out.println（encrypt（message，3））; 
 System.out.println（decrypt（encrypt（message，3），3））; 
 sc.close（）; 
} 
} 
  

运行：

 输入纯文本：
 Reem LA 
输入密钥：
 2 
密码文本
  

解决方案

使用 indexOf 不是非常有效...您可以在 char 值上执行整数运算以获取其索引。

我在代码中添加了注释来解释更多，但这是我想出来的。

  public class CaesarCipher {
 //旋转一个字符k位置
 public static char cipher c，int k）{
 //声明一些帮助常量
 final int alphaLength = 26; 
 final char asciiShift = Character.isUpperCase（c）？ 'A'：'a' 
 final int cipherShift = k％alphaLength; 
 
 //转移到0..25为a..z 
 char shif =（char）（c  -  asciiShift）; 
 //旋转字母并处理负面和值的wrap-around> = 26 
 shif =（char）（（shift + cipherShift + alphaLength）％alphaLength）; 
 //换回英文字符
 return（char）（shift + asciiShift）; 
} 
 
 //旋转一个字符串k位置
 public static String cipher（String s，int k）{
 StringBuilder sb = new StringBuilder（）; （int i = 0; i< s.length（）; i ++）{
 sb.append（cipher（s.charAt（i），k））; 
 
} 
 return sb.toString（）; 
} 
 
 public static void main（String [] args）{
扫描仪键盘=新的扫描仪（System.in）; 
字符串密码; 
 int key; 
 
 System.out.print（请输入密码：）; 
 password = keyboard.nextLine（）; 
 
 do {
 System.out.print（请输入1-25之间的键：）; 
 key = keyboard.nextInt（）; 
 
 if（key< 1 || key> 25）{
 System.out.printf（该键必须介于1和25之间，您输入％d.\\\
 ，键）; 
} 
} while（key< 1 || key> 25）; 
 
 
 System.out.println（密码：\t+密码）; 
字符串加密=密码（密码，密钥）; 
 System.out.println（加密：\t+加密）; 
 System.out.println（Decrypted：\t+ cipher（encryption，-key））; 
 
} 
} 
  

输出应该是像/ p>

 请输入密码：ABCDEFGHIJKLMNOPQRSTUVWXYZ 
请输入1-25：1之间的密钥
密码：ABCDEFGHIJKLMNOPQRSTUVWXYZ 
加密：BCDEFGHIJKLMNOPQRSTUVWXYZA 
解密：ABCDEFGHIJKLMNOPQRSTUVWXYZ 
  

i did caesar cipher code by java it runs but doesnt encrypt anything after user enter the key !

here is my code

public class CaesarCipher
{
    public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz";

    public static String encrypt(String plainText, int shiftKey)
    {
        plainText = plainText.toLowerCase();
        String cipherText = "";
        for (int i = 0; i < plainText.length(); i++)
        {
            int charPosition = ALPHABET.indexOf(plainText.charAt(i));
            int keyVal = (shiftKey + charPosition) % 26;
            char replaceVal = ALPHABET.charAt(keyVal);
            cipherText += replaceVal;
        }
        return cipherText;
    }

    public static String decrypt(String cipherText, int shiftKey)
    {
        cipherText = cipherText.toLowerCase();
        String plainText = "";
        for (int i = 0; i < cipherText.length(); i++)
        {
            int charPosition = ALPHABET.indexOf(cipherText.charAt(i));
            int keyVal = (charPosition - shiftKey) % 26;
            if (keyVal < 0)
            {
                keyVal = ALPHABET.length() + keyVal;
            }
            char replaceVal = ALPHABET.charAt(keyVal);
            plainText += replaceVal;
        }
        return plainText;
    }

    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the String for Encryption: ");
        String message = new String();
        message = sc.next();
        System.out.println(encrypt(message, 3));
        System.out.println(decrypt(encrypt(message, 3), 3));
        sc.close();
    }
}

run:

Enter The Plain Text:
Reem LA
Enter The Key:
2
The Cipher Text

解决方案

Using indexOf is not very efficient... You can do integer arithmetic on char values to get their indices.

I included comments in the code to explain more, but this is what I came up with.

public class CaesarCipher {
    // Rotate a character k-positions
    public static char cipher(char c, int k) {
        // declare some helping constants
        final int alphaLength = 26;
        final char asciiShift = Character.isUpperCase(c) ? 'A' : 'a';
        final int cipherShift = k % alphaLength;

        // shift down to 0..25 for a..z
        char shifted = (char) (c - asciiShift);
        // rotate the letter and handle "wrap-around" for negatives and value >= 26
        shifted = (char) ((shifted + cipherShift + alphaLength) % alphaLength);
        // shift back up to english characters
        return (char) (shifted + asciiShift);
    }

    // Rotate a string k-positions
    public static String cipher(String s, int k) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            sb.append(cipher(s.charAt(i), k));
        }
        return sb.toString();
    }

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        String password;
        int key;

        System.out.print("Please enter a password: ");
        password = keyboard.nextLine();

        do {
            System.out.print("Please enter a key between 1-25: ");
            key = keyboard.nextInt();

            if (key < 1 || key > 25) {
                System.out.printf(" The key must be between 1 and 25, you entered %d.\n", key);
            }
        } while (key < 1 || key > 25);


        System.out.println("Password:\t" + password);
        String encryption = cipher(password, key);
        System.out.println("Encrypted:\t" + encryption);
        System.out.println("Decrypted:\t" + cipher(encryption, -key));

    }
}

The output should be something like

Please enter a password: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Please enter a key between 1-25: 1
Password:   ABCDEFGHIJKLMNOPQRSTUVWXYZ
Encrypted:  BCDEFGHIJKLMNOPQRSTUVWXYZA
Decrypted:  ABCDEFGHIJKLMNOPQRSTUVWXYZ

这篇关于java caesar密码的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！