Java凯撒密码

Question

在这个凯撒密码中，我获得了不正确的大写字母输出。 代码如下：

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

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

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

public static void main(String[] args)
{
    String message1 = "ABCDEFGHIJKLMOPQRSTUVWXYZ";
    System.out.println(encrypt(message1, 3));
    System.out.println(decrypt(encrypt(message1, 3), 3));
    System.out.println(encrypt(message1.toLowerCase(),5));   
    System.out.println(decrypt(encrypt(message1.toLowerCase(),5),5));  

}
}

输出看起来像： ccccccccccccccccccccccccc zzzzzzzzzzzzzzzzzzzzzzz fghijklmnopqrtuvwxyzabcde abcdefghijklmopqrstuvwxyz

所需的输出是： DEFGHIJKLMOPQRSTUVWXYZABC ABCDEFGHIJKLMOPQRSTUVWXYZ fghijklmnopqrtuvwxyzabcde abcdefghijklmopqrstuvwxyz

Answer 1

问题是您将大写字母传递给方法indexOf() ，该方法检查ALPHABET但未找到它，因此它返回-1。 您需要将大写字母转换为小写字母，或者添加大写字母。

我的解决方案，将大写字母转换为小写字母然后加密/解密是：

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

public static String encrypt(String pt, int shiftKey){
    String ct = "";
    for (int i = 0; i < pt.length(); i++){
        char letter = pt.charAt(i);
        boolean upperCase = false;
        if((int)letter < 91){
            letter = (char)((int)letter + 32);
            upperCase = true;
        }
        int charPosition = ALPHABET.indexOf(letter);
        int keyVal = (shiftKey + charPosition) % 26;
        char replaceVal = ALPHABET.charAt(keyVal);
        if(upperCase){
            replaceVal = (char)((int)replaceVal - 32);
        }
        ct += replaceVal;
    }
    return ct;
}

public static String decrypt(String ct, int shiftKey){
    String pt = "";
    for (int i = 0; i < ct.length(); i++){
        char letter = ct.charAt(i);
        boolean upperCase = false;
        if((int)letter < 91){
            letter = (char)((int)letter + 32);
            upperCase = true;
        }
        int charPosition = ALPHABET.indexOf(letter);
        int keyVal = (charPosition - shiftKey) % 26;
        if (keyVal < 0){
            keyVal = ALPHABET.length() + keyVal;
        }
        char replaceVal = ALPHABET.charAt(keyVal);
        if(upperCase){
            replaceVal = (char)((int)replaceVal - 32);
        }
        pt += replaceVal;
    }
    return pt;
}

public static void main(String[] args){
    String message1 = "ABCDEFGHIJKLMOPQRSTUVWXYZ";
    System.out.println(encrypt(message1, 3));
    System.out.println(decrypt(encrypt(message1, 3), 3));
    System.out.println(encrypt(message1.toLowerCase(),5));   
    System.out.println(decrypt(encrypt(message1.toLowerCase(),5),5));  
}
}

Answer 2

这是一个解决方案，

private static final List<String> upperAlphabets = Arrays.asList(
            "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");

    private static final List<String> upperAlphabetsRev = Arrays.asList(
            "Z", "Y", "X", "W", "V", "U", "T",
            "S", "R", "Q", "P", "O", "N", "M",
            "L", "K", "J", "I", "H", "G", "F",
            "E", "D", "C", "B", "A");

    private static List<String> lowerAlphabets = new ArrayList<>();
    private static List<String> lowerAlphabetsRev = new ArrayList<>();

    private static void init() {
        for (String c : upperAlphabets) {
            lowerAlphabets.add(c.toLowerCase());
        }

        for (String c : upperAlphabetsRev) {
            lowerAlphabetsRev.add(c.toLowerCase());
        }
    }


public static String encryptCaesar(String toEncrypt, int shiftTo) throws IllegalArgumentException {

        if (shiftTo >= 26 || shiftTo < 0) {
            throw new IllegalArgumentException("shiftTo should be lesser than 26 and greater than 0");
        }

        char[] encryptedString = new char[toEncrypt.length()];
        int position = -1, pos, newPos;
        boolean upper;
        for (char c : toEncrypt.toCharArray()) {
            position++;
            pos = upperAlphabets.indexOf(String.valueOf(c));
            if (pos == -1) {
                upper = false;
                pos = lowerAlphabets.indexOf(String.valueOf(c));
            } else {
                upper = true;
            }

            newPos = (pos + shiftTo) % 26;

            encryptedString[position] = upper ? upperAlphabets.get(newPos).charAt(0) : lowerAlphabets.get(newPos).charAt(0);
        }

        return String.valueOf(encryptedString);
    }

    public static String decryptCaesar(String toDecrypt, int shiftTo) {
        if (shiftTo >= 26 || shiftTo < 0) {
            throw new IllegalArgumentException("shiftTo should be lesser than 26 and greater than 0");
        }

        char[] decryptedString = new char[toDecrypt.length()];
        int position = -1, pos, newPos;
        boolean upper;
        for (char c : toDecrypt.toCharArray()) {
            position++;
            pos = upperAlphabetsRev.indexOf(String.valueOf(c));
            if (pos == -1) {
                upper = false;
                pos = lowerAlphabetsRev.indexOf(String.valueOf(c));
            } else {
                upper = true;
            }

            newPos = (pos + shiftTo) % 26;

            decryptedString[position] = upper ? upperAlphabetsRev.get(newPos).charAt(0) : lowerAlphabetsRev.get(newPos).charAt(0);
        }

        return String.valueOf(decryptedString);
    }