# Caesar Cipher Java Program ISC 2017

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.io.*;
class Caesar{
public static void main(String args[])
throws IOException{
System.out.print("Enter text: ");
int len = text.length();
if(len < 4 || len > 99){
System.out.println("INVALID LENGTH");
return;
}
String cipher = "";
for(int i = 0; i < len; i++){
char ch = text.charAt(i);
if(Character.isLetter(ch)){
if(Character.isUpperCase(ch)){
if(ch > 'M')
cipher += (char)(ch - 13);
else
cipher += (char)(ch + 13);
}
else{
if(ch > 'm')
cipher += (char)(ch - 13);
else
cipher += (char)(ch + 13);
}
}
else
cipher += ch;
}
System.out.println("The cipher text is:\n" + cipher);
}
}``````

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