AESService.java

package ftn.security.minikms.service;

import ftn.security.minikms.entity.KeyMaterial;

import javax.crypto.*;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Base64;

public class AESService implements ICryptoService {
    public KeyMaterial generateKey() throws NoSuchAlgorithmException {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(256, SecureRandom.getInstanceStrong());
        var key = keyGenerator.generateKey();
        return KeyMaterial.of(key);
    }
    public String encrypt(String input, KeyMaterial key) throws NoSuchAlgorithmException,
            NoSuchPaddingException, IllegalBlockSizeException, BadPaddingException,
            InvalidAlgorithmParameterException, InvalidKeyException {
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");

        byte[] iv = new byte[12];
        SecureRandom random = new SecureRandom();
        random.nextBytes(iv);
        GCMParameterSpec gcmSpec = new GCMParameterSpec(128, iv);

        SecretKey secretKey = new SecretKeySpec(key.getKey(),"AES");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey, gcmSpec);

        byte[] cipherText = cipher.doFinal(input.getBytes(StandardCharsets.UTF_8));

        ByteBuffer byteBuffer = ByteBuffer.allocate(iv.length + cipherText.length);
        byteBuffer.put(iv);
        byteBuffer.put(cipherText);

        return Base64.getEncoder().encodeToString(byteBuffer.array());
    }
    public String decrypt(String encrypted, KeyMaterial key)
            throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidAlgorithmParameterException, InvalidKeyException,
            BadPaddingException, IllegalBlockSizeException {
        byte[] decoded = Base64.getDecoder().decode(encrypted);
        ByteBuffer byteBuffer = ByteBuffer.wrap(decoded);

        byte[] iv = new byte[12];
        byteBuffer.get(iv);

        byte[] cipherText = new byte[byteBuffer.remaining()];
        byteBuffer.get(cipherText);

        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        SecretKey secretKey = new SecretKeySpec(key.getKey(),"AES");
        GCMParameterSpec gcmSpec = new GCMParameterSpec(128, iv);

        cipher.init(Cipher.DECRYPT_MODE, secretKey, gcmSpec);
        byte[] plainText = cipher.doFinal(cipherText);
        return new String(plainText, StandardCharsets.UTF_8);
    }
}