RGSS(2) Encrypter source code

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.swing.JOptionPane;

public class Encrypt {
    private static int factor1 = 1;
    private static int factor2 = 256;
    private static int factor3 = 256*256;
    private static int factor4 = 256*256*256;
    private static int salt_multiplier = 7;
    private static int salt_addition = 3;

    private static InputStream is;
    private static OutputStream os;
    private static long key;
    private static byte[] header = "RGSSAD\000\001".getBytes();
    private static final String[] dirs = {"Data", "Graphics"};

    private static byte[] writeFiledata(long length) throws IOException {
        byte[] result = new byte[(int) length];
        long x = 0;
        int offset = 0;
        while (offset < length - 3) {
            x = readLong(is) ^ key;
            os.write((byte) x);
            os.write((byte) (x / factor2));
            os.write((byte) (x / factor3));
            os.write((byte) (x / factor4));
            key = changeKey(key);
            offset += 4;
        }
        if (offset < length) {
            x = readLong(is, (int) (length-offset)) ^ key;
            os.write((byte) x);
            if (offset < length - 1) {
                os.write((byte) (x / factor2));
            }
            if (offset < length - 2) {
                os.write((byte) (x / factor3));
            }
            key = changeKey(key);
        }
        return result;
    }

    private static void writeFilename(String filename, long length) throws IOException {
        long x = 0;
        for (int i = 0; i < length; i++) {
            x = (filename.charAt(i) ^ (key & 0xFFL));
            os.write((int)x);
            key = changeKey(key);
        }
    }

    private static long changeKey(long key) {
        return (key * salt_multiplier + salt_addition) & 0xFFFFFFFFL;
    }

    private static long readLong(InputStream is) throws IOException {
        long i1 = is.read();
        long i2 = is.read();
        long i3 = is.read();
        long i4 = is.read();
        return i1*factor1 + i2*factor2 + i3*factor3 + i4*factor4;
    }

    private static long readLong(InputStream is, int length) throws IOException {
        long i1 = is.read();
        long i2 = 0;
        long i3 = 0;
        if (length > 1)
            i2 = is.read();
        if (length > 2)
            i3 = is.read();
        return i1*factor1 + i2*factor2 + i3*factor3;
    }

    private static void writeLong(long l) throws IOException {
        int b1 = (int) (l % factor2) / factor1;
        int b2 = (int) (l % factor3) / factor2;
        int b3 = (int) (l % factor4) / factor3;
        int b4 = (int) (l / factor4);
        os.write(b1);
        os.write(b2);
        os.write(b3);
        os.write(b4);
    }

    private static void encryptFiles(File directory) throws IOException {
        for (File file :  directory.listFiles()) {
            if (file.isDirectory())
                encryptFiles(file);
            else
            {
                encryptFile(file);
            }
        }
    }

    public static void main(String[] args) {
        doEncryption();
    }

    public static void doEncryption() {
        boolean success = false;
        for (String dirString : dirs) {
            if (new File(dirString).isDirectory()) {
                success = true;
            }
        }
        if (!success) {
            JOptionPane.showMessageDialog(null, "Nothing to encrypt");
            return;
        }

        Object[] options = { "RPG Maker XP", "RPG Maker VX", "Cancel" };
        int i = JOptionPane.showOptionDialog(null, "Choose encryption type:",
                "RPG Maker XP/VX Encrypter", JOptionPane.DEFAULT_OPTION,
                JOptionPane.QUESTION_MESSAGE, null, options, options[0]);

        String filename = "";
        switch (i) {
        case 0:
            filename = "Game.rgssad";
            break;
        case 1:
            filename = "Game.rgss2a";
            break;
        default:
            return;
        }

        try {
            key = 0xDEADCAFEL;
            os = new BufferedOutputStream(new FileOutputStream(filename));

            // Write the header
            os.write(header);

            // Encrypt all the files in the relevant directories
            for (String dirString : dirs) {
                File dir = new File(dirString);
                if (dir.isDirectory()) {
                    encryptFiles(dir);
                }
            }

            os.close();

            JOptionPane.showMessageDialog(null, "Encryption completed!");
        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, "Encryption failed!", "An error has occurred",
                    JOptionPane.ERROR_MESSAGE);
        }
    }

    public static void encryptFile(File file) throws IOException {
        is = new BufferedInputStream(new FileInputStream(file));

        String path = file.getPath();
        // Write the size of the filename
        long size = path.length() ^ key;
        writeLong(size);
        // Change the key
        key = changeKey(key);
        // Write the filename
        writeFilename(path, path.length());
        // Write the size of the file data
        size = file.length() ^ key;
        writeLong(size);
        // Change the key
        key = changeKey(key);
        // Remember the key
        long rkey = key;
        // Write the file data
        writeFiledata(file.length());
        // Restore key
        key = rkey;

        is.close();
    }
}