EncryptionUtil.java

import javax.crypto.*;
import javax.crypto.spec.IvParameterSpec;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Base64;

public class EncryptionUtil {



    public static SecretKey generateKey(int n) throws NoSuchAlgorithmException {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(n);
        SecretKey key = keyGenerator.generateKey();
        return key;
    }


    public static byte[] generateIv() {
        byte[] iv = new byte[16];
        new SecureRandom().nextBytes(iv);
        return iv;

    }

    public static String encrypt( String input, SecretKey key, byte[] iv) throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidAlgorithmParameterException, InvalidKeyException,
            BadPaddingException, IllegalBlockSizeException {

        String algorithm = "AES/CBC/PKCS5Padding";

        IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.ENCRYPT_MODE, key, ivParameterSpec);
        byte[] cipherText = cipher.doFinal(input.getBytes());
        return Base64.getEncoder()
                .encodeToString(cipherText);
    }

    public static String decrypt( String cipherText, SecretKey key, byte[] iv) throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidAlgorithmParameterException, InvalidKeyException,
            BadPaddingException, IllegalBlockSizeException {

        String algorithm = "AES/CBC/PKCS5Padding";

        IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);



        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.DECRYPT_MODE, key, ivParameterSpec);
        byte[] plainText = cipher.doFinal(Base64.getDecoder()
                .decode(cipherText));
        return new String(plainText);
    }


    public static String getMac(SecretKey key, String cipherText) throws NoSuchAlgorithmException, InvalidKeyException {
        Mac mac = Mac.getInstance("HmacSHA256");
        mac.init(key);

        byte[] bytes = cipherText.getBytes();
        byte[] macResult = mac.doFinal(bytes);
        return new String(macResult);
    }


}