Decrypt.jar

package org.matthi.decrypt;

import java.io.*;
import javax.swing.JFileChooser;

public class App
{
    public static void main(String[] args)
        throws Exception
    {
        JFileChooser chooser = new JFileChooser();
        chooser.setDialogTitle("Verschlüsselte Datei wählen...");
        chooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
        if(chooser.showOpenDialog(null) != JFileChooser.APPROVE_OPTION)
        {
            System.exit(1);
        }

        File file = chooser.getSelectedFile();
        final byte[] key = new byte[4096];
        App.class.getResourceAsStream("/decrypt.key").read(key);

        InputStream source = new BufferedInputStream(new FileInputStream(file));
        OutputStream target = new BufferedOutputStream(new FileOutputStream(targetName(file)));

        int pos = 0;
        while(source.available() > 0)
        {
            if(pos < 4096)
            {
                target.write(source.read() ^ key[pos]);
                pos++;
            }
            else
            {
                target.write(source.read());
            }
        }

        target.flush();
        target.close();
        source.close();
    }

    private static String targetName(File file)
    {
        return file.getParent() + File.separator + file.getName().substring(7, file.getName().length() - 5);
    }
}