CNS Lab Exercise-8

EXERCISE – 8

Write a Java program to implement the RSA Algorithm using Java Cryptography.

---

✅ Step 1: Create Java Program

Create a new file named:

RSAExample.java

Now copy and paste the following code:

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import javax.crypto.Cipher;
import java.util.Base64;

public class RSAExample {

    public static void main(String[] args) {

        try {

            String text = "Hello world";

            // Generate RSA Key Pair
            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
            keyGen.initialize(2048); // Key size
            KeyPair pair = keyGen.generateKeyPair();

            PublicKey publicKey = pair.getPublic();
            PrivateKey privateKey = pair.getPrivate();

            // Create Cipher object
            Cipher cipher = Cipher.getInstance("RSA");

            // Encrypt using Public Key
            cipher.init(Cipher.ENCRYPT_MODE, publicKey);
            byte[] encryptedBytes = cipher.doFinal(text.getBytes());
            String encryptedText = Base64.getEncoder().encodeToString(encryptedBytes);

            System.out.println("Original Text: " + text);
            System.out.println("Encrypted Text: " + encryptedText);

            // Decrypt using Private Key
            cipher.init(Cipher.DECRYPT_MODE, privateKey);
            byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
            String decryptedText = new String(decryptedBytes);

            System.out.println("Decrypted Text: " + decryptedText);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

---

✅ Step 2: Compile the Program

javac RSAExample.java

If there are no errors, compilation is successful.

---

✅ Step 3: Run the Program

java RSAExample

You will see output like:

Original Text: Hello world
Encrypted Text: ksjdfhksjdfhksjdfhksjdfhksjdfh==
Decrypted Text: Hello world

Note: Encrypted text will be different every time because RSA generates new keys each run.

---

🎯 How RSA Works

• RSA generates a Public Key and Private Key.
• Public Key is used to Encrypt data.
• Private Key is used to Decrypt data.
• It is an Asymmetric Encryption Algorithm.

---

✅ Result

• RSA key pair generated successfully
• Text encrypted using Public Key
• Text decrypted using Private Key