Caesar Cipher ISC Computer Science 2017 Practical

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;
class CaesarCipher{
    public static void main(String args[]){
        Scanner in = new Scanner(System.in);
        System.out.print("Enter the string: ");
        String s = in.nextLine();
        if(s.length() < 4 || s.length() > 99){
            System.out.println("INVALID LENGTH");
            return;
        }
        String c = "";
        for(int i = 0; i < s.length(); i++){
            char ch = s.charAt(i);
            if((ch >= 'A' && ch <= 'M') || (ch >= 'a' && ch <= 'm'))
                c += (char)(ch + 13);
            else if((ch >= 'N' && ch <= 'Z') || (ch >= 'n' && ch <= 'z'))
                c += (char)(ch - 13);
            else
                c += ch;
        }
        System.out.println(c);
    }
}