stocks-be/src/main/java/com/danielbohry/stocks/service/EncryptService.java

package com.danielbohry.stocks.service;

import com.danielbohry.stocks.exception.DecryptionKeyException;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;
import java.util.Base64;

@Service
public class EncryptService {

    @Value("${encryption.key}")
    private String secret;

    private static final String ALGORITHM = "AES/CBC/PKCS5Padding";
    private static final int IV_LENGTH = 16;
    private static final int AES_KEY_SIZE = 16;

    public String encrypt(String data) throws Exception {
        SecretKeySpec key = getSecretKey();

        byte[] iv = new byte[IV_LENGTH];
        new SecureRandom().nextBytes(iv);
        IvParameterSpec ivSpec = new IvParameterSpec(iv);

        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);

        byte[] encrypted = cipher.doFinal(data.getBytes(StandardCharsets.UTF_8));
        byte[] combined = new byte[IV_LENGTH + encrypted.length];
        System.arraycopy(iv, 0, combined, 0, IV_LENGTH);
        System.arraycopy(encrypted, 0, combined, IV_LENGTH, encrypted.length);

        return Base64.getEncoder().encodeToString(combined);
    }

    public String decrypt(String encryptedData) throws Exception {
        try {
            SecretKeySpec key = getSecretKey();

            byte[] combined = Base64.getDecoder().decode(encryptedData);
            byte[] iv = new byte[IV_LENGTH];
            byte[] encrypted = new byte[combined.length - IV_LENGTH];

            System.arraycopy(combined, 0, iv, 0, IV_LENGTH);
            System.arraycopy(combined, IV_LENGTH, encrypted, 0, encrypted.length);

            Cipher cipher = Cipher.getInstance(ALGORITHM);
            cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));

            byte[] decrypted = cipher.doFinal(encrypted);
            return new String(decrypted, StandardCharsets.UTF_8);
        } catch (BadPaddingException e) {
            throw new DecryptionKeyException("Cannot decrypt data", e);
        }
    }

    private SecretKeySpec getSecretKey() {
        byte[] keyBytes = new byte[AES_KEY_SIZE];
        byte[] secretBytes = secret.getBytes(StandardCharsets.UTF_8);

        int length = Math.min(secretBytes.length, AES_KEY_SIZE);
        System.arraycopy(secretBytes, 0, keyBytes, 0, length);

        return new SecretKeySpec(keyBytes, "AES");
    }
}