java凯撒密码

Question

我用 java 做了凯撒密码运行s 但在用户输入密钥后没有加密任何东西！

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 = "";
        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();
    }
}

运行:

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

Answer 1

试试这个：

import java.util.*;

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++)
    {
        char replaceVal = plainText.charAt(i);
        int charPosition = ALPHABET.indexOf(replaceVal);        
        if(charPosition != -1) {
            int keyVal = (shiftKey + charPosition) % 26;
            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++)
    {
        char replaceVal = cipherText.charAt(i);
        int charPosition = ALPHABET.indexOf(replaceVal);
        if(charPosition != -1) {
            int keyVal = (charPosition - shiftKey) % 26;
            if (keyVal < 0) {
                keyVal = ALPHABET.length() + keyVal;
            }   
            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.nextLine();
    System.out.println(encrypt(message, 3));
    System.out.println(decrypt(encrypt(message, 3), 3));
    sc.close();
}
}

这适用于所有字母字符串...但是根据您的程序，这会将原始消息转换为小写。所以这不是纯加密，因为您的程序不区分大小写。

如果你想让你的程序区分大小写，这里是程序：

import java.util.*;

public class CaesarCipher
{ 
public static final String ALPHABET_LOWER = "abcdefghijklmnopqrstuvwxyz";
public static final String ALPHABET_UPPER = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
public static String encrypt(String plainText, int shiftKey)
{
    String cipherText = "";
    for (int i = 0; i < plainText.length(); i++)
    {
        int charPosition = -1;
        char replaceVal;
        int keyVal = -1;
        char val = plainText.charAt(i);
        System.out.println(val);
        if(Character.isUpperCase(val)) {
            charPosition = ALPHABET_UPPER.indexOf(val);
            if(charPosition != -1) {
                keyVal = (shiftKey + charPosition) % 26;
                replaceVal = ALPHABET_UPPER.charAt(keyVal);
            } else {
                replaceVal = plainText.charAt(i);
            }           
        } else {
            charPosition = ALPHABET_LOWER.indexOf(val);
            if(charPosition != -1) {
                keyVal = (shiftKey + charPosition) % 26;
                replaceVal = ALPHABET_LOWER.charAt(keyVal);
            } else {
                replaceVal = plainText.charAt(i);
            }
        }       
        System.out.println("Cipher: "+cipherText);
        cipherText += replaceVal;        
    }
    return cipherText;
}

public static String decrypt(String cipherText, int shiftKey)
{
    String plainText = "";
    for (int i = 0; i < cipherText.length(); i++)
    {
        int charPosition = -1;
        char replaceVal;
        int keyVal = -1;
        char val = cipherText.charAt(i);

        if(Character.isUpperCase(val)) {
            charPosition = ALPHABET_UPPER.indexOf(val);
            if(charPosition != -1) {
                keyVal = (charPosition - shiftKey) % 26;
                if (keyVal < 0) {
                    keyVal = ALPHABET_UPPER.length() + keyVal;
                }
                replaceVal = ALPHABET_UPPER.charAt(keyVal);
            } else {
                replaceVal = cipherText.charAt(i);
            }           
        } else {
            charPosition = ALPHABET_LOWER.indexOf(val);
            if(charPosition != -1) {
                keyVal = (charPosition - shiftKey) % 26;
                if (keyVal < 0) {
                    keyVal = ALPHABET_LOWER.length() + keyVal;
                }
                replaceVal = ALPHABET_LOWER.charAt(keyVal);
            } else {
                replaceVal = cipherText.charAt(i);
            }
        }
        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.nextLine();
    System.out.println(encrypt(message, 3));
    System.out.println(decrypt(encrypt(message, 3), 3));
    sc.close();
}
}

希望这能提供一些思路。祝一切顺利。

Answer 2

使用 indexOf 不是很有效...您可以对 char 值进行整数运算以获得它们的索引。

我在代码中加入了注释来解释更多，但这是我想出的。

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));

    }
}

输出应该类似于

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

Answer 3

这可能是最简单也最容易理解的方法：

import java.util.*;
public class CeaserCipher {
   public static void main (String [] args) {
      Scanner input = new Scanner(System.in);
      System.out.print("Type your message ");
      String message = input.nextLine().toUpperCase();
      System.out.print("Set Encoding Key ");
      int key = input.nextInt() % 26;
      for (int i = 0; i < message.length(); i++) {
         char c = message.charAt(i);
         if (c <= 64 || c >= 91) {
            c += 0;
          }
         else {
            c += key;
            if (c >= 91) {
               c -= 26;
            }
         }
         System.out.print(c);
      }
   }
}

Answer 4

private static final int ALPHABET_SIZE = 26;

public static String encryptOrDecrypt(String str, int rotateBy, boolean isEncryption) {
    rotateBy = rotateBy % 26;
    StringBuilder result = new StringBuilder();
    for (int i = 0; i < str.length(); i++) {
        char temp = str.charAt(i);
        temp = rotate(temp, rotateBy,isEncryption);
        result.append(temp);
    }
    return result.toString();
}
private static char rotate(char c, int rotateBy,boolean isEncryption) {
    int start=0;
    int end =0;
    if (isLowerCase(c)) {
        start='a';
        end = 'z';
    } else if (isUpperCase(c)) {
        start='A';
        end = 'Z';
    }else {
        return c;
    }
    if (isEncryption){
        c += rotateBy;
    }else {
        c -= rotateBy;
    }

    if (c < start) {
        return (char) (c + ALPHABET_SIZE);
    }
    if (c > end) {
        return (char) (c - ALPHABET_SIZE);
    }
    return c;
}
public static void main(String args[]) {
    String planeText= "TrilokiNathYadav";
    System.out.println("Plane Text : "+planeText);
    String encrypted =encryptOrDecrypt(planeText,2,true);
    System.out.println("Encrypted : "+encrypted);
    String decrypted = encryptOrDecrypt(encrypted,2,false);
    System.out.println("Decrypted : "+decrypted);
}

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