Caesar Cipher Encryption and Decryption In Java

Caesar Cipher:-

Caesar cipher is one of the earliest known and simplest ciphers. It is a type of replacement cipher in which each letter of the plaintext is ‘moved’ to a certain place under the alphabet.
For example, with a shift of 1, A will be replaced by B, B becomes C, and so on.
The name of this method is named after Julius Caesar, who apparently used it to communicate with his generals.

---

Caesar Cipher Program in Java

 

Caesar Cipher Encryption

---

import java.util.Scanner;
 
public class CaesarCipher
 {
  public static void main(String args[]){
    String str_message, encrypted_Message = "";
    int key;
    char ch;
    Scanner scan = new Scanner(System.in);
    
    System.out.println("Enter a message to encrypt: ");
    str_message = scan.nextLine();
    
    System.out.println("Enter the key: ");
    key = scan.nextInt();
 
    for(int i = 0; i < str_message.length(); ++i){
      ch = str_message.charAt(i);
      
      if(ch >= 'a' && ch <= 'z'){
              ch = (char)(ch + key);
              
              if(ch > 'z'){
                  ch = (char)(ch - 'z' + 'a' - 1);
              }
              
              encrypted_Message += ch;
          }
          else if(ch >= 'A' && ch <= 'Z'){
              ch = (char)(ch + key);
              
              if(ch > 'Z'){
                  ch = (char)(ch - 'Z' + 'A' - 1);
              }
              
              encrypted_Message += ch;
          }
          else {
          	encrypted_Message += ch;
          }
    }
    
    System.out.println("Encrypted Message is : = " + encrypted_Message);
  }
}

 

---

Output:-

Example:- If you run above program then it will ask to enter the message to encrypt like below:-

Enter a message to encrypt:
walmart.com
Enter the key: –for encrypt your message
5
Encrypted Message is : = bfqrfwy.htr

 

Enter a message to encrypt:
amazon river
Enter the key: –for encrypt your message
5
Encrypted Message is : = frfets wnajw

---

Caesar Cipher Decryption

---

import java.util.Scanner;
 
public class CaesarCipher {
  public static void main(String...s){
    String str_message, decrypted_Message = "";
    int key;
    char ch;
    Scanner scan = new Scanner(System.in);
    
    System.out.println("Enter a message to decrypt: ");
    str_message = scan.nextLine();
    
    System.out.println("Enter key: ");
    key = scan.nextInt();
 
    for(int i = 0; i < str_message.length(); ++i){
      ch = str_message.charAt(i);
      
      if(ch >= 'a' && ch <= 'z'){
              ch = (char)(ch - key);
              
              if(ch < 'a'){
                  ch = (char)(ch + 'z' - 'a' + 1);
              }
              
              decrypted_Message += ch;
          }
          else if(ch >= 'A' && ch <= 'Z'){
              ch = (char)(ch - key);
              
              if(ch < 'A'){
                  ch = (char)(ch + 'Z' - 'A' + 1);
              }
              
              decrypted_Message += ch;
          }
          else {
          	decrypted_Message += ch;
          }
    }
    
    System.out.println("Decrypted Message : = " + decrypted_Message);
  }
}

 

---

Output:-

Example:- If you run above program then it will ask to enter the message to decrypt like below:-

Enter a message to decrypt:
bfqrfwy.htr
Enter key: –for decrypt your message
5
Decrypted Message : = walmart.com

---

 

Enter a message to decrypt:
frfets wnajw
Enter key: –for decrypt your message
5
Decrypted Message : = amazon river