Caesar Cipher is an encryption technique which is implemented as ROT13 ('rotate by 13 places'). It is a simple letter substitution cipher that replaces a letter with the letter 13 places after it in the alphabets, with the other characters remaining unchanged.

ROT13

A/a

B/b

C/c

D/d

E/e

F/f

G/g

H/h

I/i

J/j

K/k

L/l

M/m

↕

↕

↕

↕

↕

↕

↕

↕

↕

↕

↕

↕

↕

N/n

O/o

P/p

Q/q

R/r

S/s

T/t

U/u

V/v

W/w

X/x

Y/y

Z/z

Write a program to accept a plain text of length L, where L must be greater than 3 and less than 100.

Encrypt the text if valid as per the Caesar Cipher.

Test your program with the sample data and some random data.

Example 1

INPUT:
Hello! How are you?

OUTPUT:
The cipher text is:
Uryyb! Ubj ner lbh?

Example 2

INPUT:
Encryption helps to secure data.

OUTPUT:
The cipher text is:
Rapelcgvba urycf gb frpher qngn.

Example 3

INPUT:
You

OUTPUT:
INVALID LENGTH

import java.util.Scanner;

public class CaesarCipher
{
    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        System.out.println("Enter plain text:");
        String str = in.nextLine();
        int len = str.length();
        
        if (len <= 3 || len >= 100) {
            System.out.println("INVALID LENGTH");
            return;
        }
        
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < len; i++) {
            char ch = str.charAt(i);
            if ((ch >= 'A' && ch <= 'M') || (ch >= 'a' && ch <= 'm')) {
                sb.append((char)(ch + 13));
            }
            else if ((ch >= 'N' && ch <= 'Z') || (ch >= 'n' && ch <= 'z')) {
                sb.append((char)(ch - 13));
            }
            else {
                sb.append(ch);
            }
        }
        
        String cipher = sb.toString();
        System.out.println("The cipher text is:");
        System.out.println(cipher);
    }
}