encryption - java caesar cipher code

Question

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

Answer 1

Try this:

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();
}
}

This will work for all alphabetical strings... But as per your program, this will convert the original message to lowercase. So this is not pure encryption since your program is case insensitive.

If you want your program to be case sensitive, here is the program:

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();
}
}

Hope this gives some idea. All the best.