Java class to encrypt/decrypt strings using the AES 256 bit encryption algorithm

AES256Crypt.java

package tech.neurobyte.dev.crypt;

import org.jetbrains.annotations.Contract;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.spec.KeySpec;
import java.util.Base64;

public class AES256Crypt {

    // Member fields
    // The salt for the encryption which will be the username encrypted in DES
    private static final String cryptSalt = "NeuroByte Tech";
    // The Cipher which will be used to encrypt
    private Cipher enCipher;
    // The Cipher which will be used to decrypt
    private Cipher deCipher;
    // The random string key for the person which will be used to encrypt and decrypt details.
    private String securiKey;

    /**
     * The default constructor for the AES256Crypt class
     */
    public AES256Crypt() throws Exception {
        // Initialize the Cipher objects to encrypt and decrypt using the AES algorithm
        this.enCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        this.deCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        // Initialize the securiKey
        this.securiKey = this.randSecuriKey();

        // Creating the initialization vector for the secret key
        byte[] initVector = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
        IvParameterSpec initVectorSpec = new IvParameterSpec(initVector);
        // Setting up the secret key spec with AES
        SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        KeySpec pbeKeySpec = new PBEKeySpec(this.securiKey.toCharArray(), cryptSalt.getBytes(), 65536, 256);
        SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);
        SecretKeySpec secretKeySpec = new SecretKeySpec(secretKey.getEncoded(), "AES");

        // Initialize the cipher objects with the keys
        this.enCipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, initVectorSpec);
        this.deCipher.init(Cipher.DECRYPT_MODE, secretKeySpec, initVectorSpec);
    }

    /**
     * Constructor for the AES256Crypt class with the option to use the securiKey from the database.
     *
     * @param userSecuriKey - The securiKey stored individually for each user on the database
     */
    @Contract(pure = true)
    AES256Crypt(String userSecuriKey) throws Exception {
        // Initialize the Cipher objects to encrypt and decrypt using the AES algorithm
        this.enCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        this.deCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        // Initialize the securiKey
        this.securiKey = userSecuriKey;

        // Creating the initialization vector for the secret key
        byte[] initVector = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
        IvParameterSpec initVectorSpec = new IvParameterSpec(initVector);
        // Setting up the secret key spec with AES
        SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        KeySpec pbeKeySpec = new PBEKeySpec(this.securiKey.toCharArray(), cryptSalt.getBytes(), 65536, 256);
        SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);
        SecretKeySpec secretKeySpec = new SecretKeySpec(secretKey.getEncoded(), "AES");

        // Initialize the cipher objects with the keys
        this.enCipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, initVectorSpec);
        this.deCipher.init(Cipher.DECRYPT_MODE, secretKeySpec, initVectorSpec);
    }

    /**
     * Method to encrypt the given string using the AES256 algorithm
     *
     * @param stringToEncrypt - The string which has to be encrypted
     * @return The encrypted string
     */
    String encrypt(@NotNull String stringToEncrypt) throws Exception {
        // Encoding the string into a sequence of bytes using UTF8 and storing the result into a new byte array.
        byte[] stringToEncryptBytes = stringToEncrypt.getBytes(StandardCharsets.UTF_8);
        byte[] encryptedStringBytes = this.enCipher.doFinal(stringToEncryptBytes);
        // Convert the encryptedString bytes to a String object

        // Returning encrypted String
        return Base64.getEncoder().encodeToString(encryptedStringBytes);
    }

    /**
     * Method to decrypt the given cipher using the AES256 algorithm
     *
     * @param cipherToDecrypt - The cipher which has to be decrypted
     * @return The decrypted string
     */
    @Nullable
    String decrypt(@NotNull String cipherToDecrypt) throws Exception {
        // Decoding the cipher using BASE64 and deciphering the bytes
        byte[] cipherToDecryptBytes = Base64.getDecoder().decode(cipherToDecrypt.getBytes());
        byte[] decryptedCipherBytes = this.deCipher.doFinal(cipherToDecryptBytes);

        // Return the deciphered String after formatting in UTF8
        return new String(decryptedCipherBytes, StandardCharsets.UTF_8);
    }

    /**
     * A method to build a securiKey using random Alpha-Numeric characters
     *
     * @return A SecuriKey of random Alpha-Numeric characters
     */
    @NotNull
    private String randSecuriKey() {

        // Preparation
        // The list of Alpha-numeric characters that will be used to create the random string
        final String ALPHA_NUMERIC_STRING = Cortex.configCatClient.getValue(String.class, "aes256cryptListOfEncryptionCharacters", Cortex.databaseManager.getConfigCatUser(), "Default");
        // The length of the securiKey
        int securiKeyLength = Cortex.configCatClient.getValue(Integer.class, "aes256cryptSecurikeyLength", Cortex.databaseManager.getConfigCatUser(), 0);

        StringBuilder randStringBuilder = new StringBuilder();
        while (securiKeyLength-- != 0) {
            int character = (int) (Math.random() * ALPHA_NUMERIC_STRING.length());
            randStringBuilder.append(ALPHA_NUMERIC_STRING.charAt(character));
        }

        return randStringBuilder.toString();
    }
}