ctf2.java

package com.company;

import org.bouncycastle.jce.provider.BouncyCastleProvider;

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 javax.xml.bind.DatatypeConverter;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.security.Security;

public class Main
{

    public static void main(String[] args) throws Exception
    {
        try
        {
            String PASSWORD = "JB_MR1.1";
            String IV = "A70DC03BF2D64B036A845F15531A7E74";
            String SALT = "3BC5AC2EB90BA29C02A0CA0286B0CFCB";
            String TRANSFORMATION = "AES/CBC/PKCS5Padding";
            String ALGORITHM = "PBEwithSHA256and256bitAES-CBC-BC";
            byte[] iv = toByteArray(IV);
            byte[] salt = toByteArray(SALT);
            Security.addProvider(new BouncyCastleProvider());

            PBEKeySpec ks = new PBEKeySpec(PASSWORD.toCharArray(), salt, 1000, 256);
            SecretKeyFactory skf = SecretKeyFactory.getInstance(ALGORITHM);
            SecretKey secretKey = skf.generateSecret(ks);
            SecretKeySpec newKey = new SecretKeySpec(secretKey.getEncoded(), "AES");

            Cipher cipher = Cipher.getInstance(TRANSFORMATION);
            cipher.init(Cipher.DECRYPT_MODE, newKey, new IvParameterSpec(iv));
            byte[] data = loadFile();
            //data = Arrays.copyOfRange(data, 32, data.length);
            byte[] decData = cipher.doFinal(data);
            saveFile(decData);
        }
        catch(Exception ex)
        {
            System.out.println(ex.getMessage());
        }
    }

    private static void saveFile(byte[] bytes) throws IOException
    {
        FileOutputStream fos = new FileOutputStream("/home/alex/data.decrypted");
        fos.write(bytes);
        fos.close();
    }

    private static byte[] loadFile() throws IOException
    {
        RandomAccessFile f = new RandomAccessFile("/home/alex/Downloads/data.bin", "r");
        byte[] b = new byte[(int)f.length()];
        f.read(b);
        return b;
    }


    public static byte[] toByteArray(String s) {
        return DatatypeConverter.parseHexBinary(s);
    }
}