AES_in_Java

import javax.crypto.*;
import javax.crypto.spec.*;
import java.security.*;
import java.util.Base64;

public class AESUtil {
    private static final int KEY_SIZE = 256;
    private static final int IV_SIZE = 16;
    private static final String ALGORITHM = "AES/CBC/PKCS5Padding";

    public static String encrypt(String plainText, SecretKey key, IvParameterSpec iv) 
            throws Exception {
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, key, iv);
        byte[] encrypted = cipher.doFinal(plainText.getBytes());
        return Base64.getEncoder().encodeToString(encrypted);
    }

    public static String decrypt(String cipherText, SecretKey key, IvParameterSpec iv) 
            throws Exception {
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, key, iv);
        byte[] plainText = cipher.doFinal(
            Base64.getDecoder().decode(cipherText)
        );
        return new String(plainText);
    }

    public static SecretKey generateKey() throws NoSuchAlgorithmException {
        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(KEY_SIZE, SecureRandom.getInstanceStrong());
        return keyGen.generateKey();
    }

    public static IvParameterSpec generateIv() {
        byte[] iv = new byte[IV_SIZE];
        SecureRandom.getInstanceStrong().nextBytes(iv);
        return new IvParameterSpec(iv);
    }
}