Caesar Cipher Java Decryption

Question

I have a problem when I'm trying to decode an encrypted message. It decrypts almost everything as it should be, but when I try to decrypt 'w x y z' (all lower case), it doesn't work properly. It only decrypts those letters when they are UPPERCASE. What did I do wrong?

@SuppressWarnings("unused")
public static void main(String[] args) {

    String message = "ABCDEFGHILMNOPQRSTU hello giordano WORLD HOW wxyZ XyZ XYZ YOU  xyz";

    System.out.println(message);
    String encr = encrypt(message);
    String decr = decrypt(encr);

    System.out.println(encr + "\n" + decr);

}



@SuppressWarnings("unused")
private static String encrypt(String message) {
    StringBuilder temp = new StringBuilder();

    for(int i=0; i<message.length(); i++) {
        char c = (char)(message.charAt(i) + 3);

        if(c >= 'x') {
            c = (char)(message.charAt(i) - 23);
        } else {
            c = (char)(message.charAt(i) + 3);
        }

        temp.append(c);
    }

    return temp.toString();
}



private static String decrypt(String message) {
    StringBuilder temp = new StringBuilder();

    for(int i=0; i<message.length(); i++) {
            char c = (char)(message.charAt(i) - 3);

        // HELLO WORLD
        // KHOOR ZRUOG

        if(c > 'x') {
            c = (char)(message.charAt(i) + 26);
        } else {
            c = (char)(message.charAt(i) - 3);
        }

        temp.append(c);
    }

    return temp.toString();
}

OUTPUT:

Text: ABCDEFGHILMNOPQRSTU hello giordano WORLD HOW wxyZ XyZ XYZ YOU  xyz
Encrypted: DEFGHIJKLOPQRSTUVWX#khoor#jlrugdqr#ZRUOG#KRZ#`ab]#[b]#[\]#\RX##abc
Decrypted: ABCDEFGHILMNOPQRSTU hello giordano WORLD HOW ]^_Z X_Z XYZ YOU  ^_`

EXPECTED OUTPUT:

Text: ABCDEFGHILMNOPQRSTU hello giordano WORLD HOW wxyZ XyZ XYZ YOU  xyz
Encrypted: DEFGHIJKLOPQRSTUVWX#khoor#jlrugdqr#ZRUOG#KRZ#`ab]#[b]#[\]#\RX##abc
Decrypted: ABCDEFGHILMNOPQRSTU hello giordano WORLD HOW wxyZ XyZ XYZ YOU  xyz

Please describe the exact intention of your code how exactly should your plain text be shifted what is the intention of each line of your code - maybe this way you solve your own question. — baxbear, Nov 26 '19 at 18:01
Shift = 3. Basically I'm developing a software server/client where the client sends a message to the server. The client transfers the encrypted message and the server decrypts it. — Lorenzo Orlando, Nov 26 '19 at 18:06

score 1 · Answer 1 · answered Nov 26 '19 at 17:58

1

The issue you are facing only for small case is because you have written this code in encrypt

        if(c >= 'x') {
            c = (char)(message.charAt(i) - 23);
        } else {
            c = (char)(message.charAt(i) + 3);
        }

and this one for decrypt

        if(c > 'x') {
            c = (char)(message.charAt(i) + 26);
        } else {
            c = (char)(message.charAt(i) - 3);
        }

they only handle small 'x' while for capital 'X' you have not written any such condition. So if you remove above mentioned code from your function it will start working. But this will not caesar-cipher, for that matter you can start looking by "how to traverse in cyclic order".

answered Nov 26 '19 at 17:58

Himanshu Singh

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If I add the condition when c >= 'X' it does not work anyway – Lorenzo Orlando Nov 26 '19 at 18:03
@LorenzoOrlando i know it won't work. You have to think it through. Food for your thought:- what if instead of replacing current character by +3rd character replace it with +150th character. Then what will be your solution. – Himanshu Singh Nov 26 '19 at 18:13
Sir I still can't find a solution. Can you just help me please? – Lorenzo Orlando Nov 26 '19 at 18:35

score 0 · Answer 2 · answered Jan 22 '21 at 18:24

After Searching and Testing found that is the correct way to decoding.

private static String decrypt(String message) {
        StringBuilder temp = new StringBuilder();
       //key = 4
        for(int i=0; i<message.length(); i++) {
                char  c = (char)((message.charAt(i) - 4 - 97) %26 +97);
                if(c < 'a') {
                    c = (char) (message.charAt(i) - 4 - 'a' + 'z' + 1);
                }
            temp.append(c);
        }

        return temp.toString();
    }

Caesar Cipher Java Decryption

2 Answers2