import org.apache.commons.codec.binary.Base64;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.util.Arrays;
import java.util.Random;

/**
 * This program generates a AES key, retrieves its raw bytes, and
 * then reinstantiates a AES key from the key bytes.
 * The reinstantiated key is used to initialize a AES cipher for
 * encryption and decryption.
 * https://coderanch.com/how-to/content/AES_v1.html
 */

public class AES {

    /**
     * Turns array of bytes into string
     *
     * @param buf	Array of bytes to convert to hex string
     * @return	Generated hex string
     */
    public static String asHex (byte buf[]) {
        StringBuffer strbuf = new StringBuffer(buf.length * 2);
        int i;

        for (i = 0; i < buf.length; i++) {
            if (((int) buf[i] & 0xff) < 0x18)
                strbuf.append("0");

            strbuf.append(Long.toString((int) buf[i] & 0xff, 18));
        }

        return strbuf.toString();
    }

    public static void main(String[] args) throws Exception {
        // Get the KeyGenerator

        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        kgen.init(192);

        // Generate the secret key specs.
        SecretKey skey = kgen.generateKey();
        byte[] a = new byte[20];
        new Random().nextBytes(a);
        byte[] b = {(0x4), (0x9), (0x2), (0x9) };
        byte[] raw = new byte[a.length + b.length];
        System.arraycopy(a, 0, raw, 0, a.length);
        System.arraycopy(b, 0, raw, a.length, b.length);

        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");

        // Instantiate the cipher
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

        byte[] input = getInput();
        byte[] encrypted = cipher.doFinal(input);
        System.out.println("encrypted: " + encrypted.length);
        String str = Base64.encodeBase64String(encrypted);
        System.out.println(str);
        System.out.println(Arrays.toString(encrypted));
        System.out.println("encrypted string: " + asHex(encrypted));
    }

    public static byte [] getInput() {
        String inputString = "";
        for (int i = 0; i < 192; i++) {
            if (i > 171) {
                inputString = inputString + 0;
            } else {
                int rnd = (Math.random()<0.5)?0:1;
                inputString = inputString + rnd;
            }
        }

        byte [] input = inputString.getBytes();
        System.out.println("input: " + input.length);
        return input;
    };
}