Encrypting configuration files

Question

I have an application and a configuration file which is xml format.To prevent the user from fiddling with the xml file with a text editor I want to only provide an encrypted version of the file in the released product which I decrypt in memory.
Ive done this using the DES algorithm but of course to decrypt the file you need to use the same key that you encrypted it with so Ive converted the key to a transparent key and written it to another file. So when the application starts it reads the key from the file and then uses it to decrypt the config file on the fly.
This works but because the key is in a plain text file it would be fairly easy for someone to recognise it as a key try it with the various known key algorithms and decode the config file. How can I avoid this, (I could encrypt the key but then I would need to store the key I encrypted it with in another file and so on,,)
Thanks Paul

Answer 1

OK,sorry I dont quite get the multiple key thing
The program below encode a file using key defined in the file then decrypts the file,if you have any spare time I would be grateful if you could explain how would I modify this t o support mutiple keys,
public class ConvertFile
    private static byte[]    rawKey={111,50,78,45,12,78,90,99};
    public static void main(String[] args)
        throws Exception
        encryptFile(new File("originalfile"),
                    new File("encryptedfile"));
        decryptFile(new File("settings.xml.decrypt"),
                    new File("encryptedfile"));
    public static SecretKey retrieveKey()
        try
            //Rebuild Transparent key and convert to secret key
            DESKeySpec keySpec = new DESKeySpec(rawKey);
            SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
            SecretKey key = keyFactory.generateSecret(keySpec);
            return key;
        catch(Exception e)
            e.printStackTrace();
            return null;
    public static void createKey()
        try
            //Create Secret key
            KeyGenerator keyGen = KeyGenerator.getInstance("DES");
            SecretKey key = keyGen.generateKey();
            //Now get transparent form of key
            SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
            DESKeySpec keySpec =(DESKeySpec)keyFactory.getKeySpec(key,javax.crypto.spec.DESKeySpec.class);
            byte[] rawKey = keySpec.getKey();
        catch (Exception e)
            e.printStackTrace();
    /** Encrypt a file */
    public static void encryptFile(File plainFile, File encryptedFile)
        try
            byte[] buf = new byte[1024];
            int len;
            //Create Cipher
            Cipher cipher = Cipher.getInstance("DES");
            cipher.init(Cipher.ENCRYPT_MODE, retrieveKey());
            //Encrypt the Data
            FileInputStream fis = new FileInputStream(plainFile);
            FileOutputStream fos = new FileOutputStream(encryptedFile);
            while ( (len = fis.read(buf)) != -1)
                fos.write(cipher.update(buf, 0, len));
            fos.write(cipher.doFinal());
            fos.close();
            fis.close();
        catch (Exception e)
            e.printStackTrace();
    /** Decrypt a file */
    public static void decryptFile(File plainFile, File encryptedFile)
        try
            byte[] buf = new byte[1024];
            int len;
            //Create Cipher
            Cipher cipher = Cipher.getInstance("DES");
            cipher.init(Cipher.DECRYPT_MODE,retrieveKey());
            //Decrypt the Data
            FileInputStream fis = new FileInputStream(encryptedFile);
            FileOutputStream fos = new FileOutputStream(plainFile);
            while ( (len = fis.read(buf)) != -1)
                fos.write(cipher.update(buf, 0, len));
            fos.write(cipher.doFinal());
            fos.close();
            fis.close();
        catch (Exception e)
            e.printStackTrace();
}