FPE in Java with BouncyCastle

FpeBouncyCastle.java

package org.example;

import org.bouncycastle.crypto.AlphabetMapper;
import org.bouncycastle.crypto.util.BasicAlphabetMapper;
import org.bouncycastle.jcajce.spec.FPEParameterSpec;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.AlgorithmParameterSpec;
import java.text.SimpleDateFormat;
import java.util.Arrays;


/**
 * Hello world!
 *
 */
public class App
{
    // explain the following code

    public static void main( String[] args ) throws Exception {
        SecretKey key = generateAESKey("12345678901234567890123456789012");
        byte[] tweak = getTweak();
        AlphabetMapper alphabetMapper = new BasicAlphabetMapper("0123456789");
        int radix = alphabetMapper.getRadix();
        char[] plaintext = "123456788".toCharArray();

        byte[] plain_bytes = alphabetMapper.convertToIndexes(plaintext);

        Cipher cipher = Cipher.getInstance("AES/FF3-1/NoPadding", new BouncyCastleProvider());
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
        System.out.println(sdf.format(System.currentTimeMillis()));
        byte[] cipher_bytes = null;
        for(int i = 0; i < 100000; i++) {
            cipher_bytes = encrypt(cipher, key, tweak, radix, plain_bytes);
        }
        System.out.println(sdf.format(System.currentTimeMillis()));
        byte[] decrypted = null;Fo
        for(int i = 0; i < 100000; i++) {
            decrypted = decrypt(cipher, key, tweak, radix, cipher_bytes);
        }
        System.out.println(sdf.format(System.currentTimeMillis()));
        char[] cipher_chars = alphabetMapper.convertToChars(cipher_bytes);
        System.out.println(new String(cipher_chars));

        char[] plain_chars = alphabetMapper.convertToChars(decrypted);
        System.out.println(new String(plain_chars));
        System.out.println( "Hello World!" );
    }

    public static SecretKeySpec generateAESKey(String password) throws Exception {

        // Convert password to bytes
        byte[] passwordBytes = password.getBytes("UTF-8");
        System.out.println("passwordBytes: " + passwordBytes.length);

        // Generate 256-bit key from password bytes using SHA-256 hash function
        MessageDigest sha = MessageDigest.getInstance("SHA-256");
        byte[] keyBytes = sha.digest(passwordBytes); // will create a 32-byte key

        // Truncate key to 128 bits (16 bytes) for use with AES
        keyBytes = Arrays.copyOf(keyBytes, 32);

        // Create secret key spec from AES key bytes
        SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "AES");

        return keySpec;
    }

    public static byte[] encrypt(Cipher cipher, SecretKey key, byte[] tweak, int radix, byte[] plaintext) throws Exception {
        AlgorithmParameterSpec fpeParameterSpec = new FPEParameterSpec(radix, tweak);
        cipher.init(Cipher.ENCRYPT_MODE, key, fpeParameterSpec);
        return cipher.doFinal(plaintext);
    }

    public static byte[] decrypt(Cipher cipher, SecretKey key, byte[] tweak, int radix, byte[] ciphertext) throws Exception {
        AlgorithmParameterSpec fpeParameterSpec = new FPEParameterSpec(radix, tweak);
        cipher.init(Cipher.DECRYPT_MODE, key, fpeParameterSpec);
        return cipher.doFinal(ciphertext);
    }

    private static SecretKey generateKey() throws NoSuchAlgorithmException {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        int keyLength = 256;
        keyGenerator.init(keyLength);
        return keyGenerator.generateKey();
    }

    private static byte[] getTweak() {
        byte[] byteArray = new byte[7];

        for (int i = 0; i < 7; i++) {
            byteArray[i] = 0;
        }

        return byteArray;
    }

    private int getRadix(String alphabet) {
        AlphabetMapper alphabetMapper = new BasicAlphabetMapper(alphabet);
        int radix = alphabetMapper.getRadix();
        return radix;
    }
}