1import javax.crypto.Cipher;
2import javax.crypto.KeyGenerator;
3import javax.crypto.SecretKey;
4import javax.crypto.spec.SecretKeySpec;
5import java.util.Base64;
6
7public class AESSymmetricEncryptionExample {
8
9    public static void main(String[] args) throws Exception {
10        // Create a key generator for AES algorithm
11        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
12        keyGen.init(128);  // Set key size (128, 192, or 256)
13
14        // Generate a secret key
15        SecretKey secretKey = keyGen.generateKey();
16
17        // Transform the key into a byte array
18        byte[] rawKey = secretKey.getEncoded();
19
20        // Create a secret key from the byte array
21        SecretKeySpec keySpec = new SecretKeySpec(rawKey, "AES");
22
23        // Encrypt
24        Cipher cipher = Cipher.getInstance("AES");
25        cipher.init(Cipher.ENCRYPT_MODE, keySpec);
26        
27        String plainText = "Hello, World!";
28        byte[] encryptedText = cipher.doFinal(plainText.getBytes());
29
30        // Encode the byte array to a base64 string for easy handling
31        String encodedText = Base64.getEncoder().encodeToString(encryptedText);
32        System.out.println("Encrypted Text: " + encodedText);
33
34        // Decrypt
35        cipher.init(Cipher.DECRYPT_MODE, keySpec);
36        byte[] decryptedText = cipher.doFinal(Base64.getDecoder().decode(encodedText));
37        System.out.println("Decrypted Text: " + new String(decryptedText));
38    }
39}

1import javax.crypto.Cipher;
2import java.security.*;
3
4public class RSAAsymmetricEncryptionExample {
5
6    public static void main(String[] args) throws Exception {
7        // Generate key pair
8        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
9        keyGen.initialize(2048);
10        KeyPair keyPair = keyGen.generateKeyPair();
11
12        PublicKey publicKey = keyPair.getPublic();
13        PrivateKey privateKey = keyPair.getPrivate();
14
15        // Encrypt
16        Cipher cipher = Cipher.getInstance("RSA");
17        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
18        
19        String plainText = "Hello, World!";
20        byte[] encryptedText = cipher.doFinal(plainText.getBytes());
21        System.out.println("Encrypted Text: " + Base64.getEncoder().encodeToString(encryptedText));
22
23        // Decrypt
24        cipher.init(Cipher.DECRYPT_MODE, privateKey);
25        byte[] decryptedText = cipher.doFinal(encryptedText);
26        System.out.println("Decrypted Text: " + new String(decryptedText));
27    }
28}