Encrypting/Decrypting files in Java

O want to encrypt and decrypt files using my Java program. These files are compiled Java .class files, I don't know what I am doing wrong. I am just testing now, but after encrypt and decrypt with the same key. It shows that file is

Exception in thread "AWT-EventQueue-0" java.lang.ClassFormatError: Truncated class file 

and that class cannot be loaded. There is my encrypter/decrypter class code:

import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import javax.crypto.Cipher; import javax.crypto.CipherInputStream; import javax.crypto.CipherOutputStream; import javax.crypto.SecretKey; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.DESKeySpec; public class EncTool { public static void encrypt(String key, String filename) throws Throwable { InputStream is = new FileInputStream("SomeFile.class"); OutputStream os = new FileOutputStream("SomeFile.class"); encrypt(key, Cipher.ENCRYPT_MODE, is, os); } public static void decrypt(String key, String filename) throws Throwable { InputStream is = new FileInputStream("SomeFile.class"); OutputStream os = new FileOutputStream("SomeFile.class"); decrypt(key, Cipher.DECRYPT_MODE, is, os); } public static void encrypt(String key, int mode, InputStream is, OutputStream os) throws Throwable { DESKeySpec dks = new DESKeySpec(key.getBytes()); SecretKeyFactory skf = SecretKeyFactory.getInstance("DES"); SecretKey desKey = skf.generateSecret(dks); Cipher cipher = Cipher.getInstance("DES"); // DES/ECB/PKCS5Padding for SunJCE cipher.init(Cipher.ENCRYPT_MODE, desKey); CipherInputStream cis = new CipherInputStream(is, cipher); doCopy(cis, os); } public static void decrypt(String key, int mode, InputStream is, OutputStream os) throws Throwable { DESKeySpec dks = new DESKeySpec(key.getBytes()); SecretKeyFactory skf = SecretKeyFactory.getInstance("DES"); SecretKey desKey = skf.generateSecret(dks); Cipher cipher = Cipher.getInstance("DES"); // DES/ECB/PKCS5Padding for SunJCE cipher.init(Cipher.DECRYPT_MODE, desKey); CipherOutputStream cos = new CipherOutputStream(os, cipher); doCopy(is, cos); } public static void doCopy(InputStream is, OutputStream os) throws IOException { byte[] bytes = new byte[64]; int numBytes; while ((numBytes = is.read(bytes)) != -1) { os.write(bytes, 0, numBytes); } os.flush(); os.close(); is.close(); } } 

and for testing im executing it that way:

 try { EncTool.encrypt("somekey123", "SomeFile"); EncTool.decrypt("somekey123", "SomeFile"); } catch (Throwable e1) { // TODO Auto-generated catch block e1.printStackTrace(); } 

What am i doing wrong? Or maybe how should it be done?

EDIT

when my code looks that:

 public static void encrypt(String key, String filename) throws Throwable { InputStream is = new FileInputStream("Somefile.class"); OutputStream os = new FileOutputStream("tempfile.class"); DESKeySpec dks = new DESKeySpec(key.getBytes()); SecretKeyFactory skf = SecretKeyFactory.getInstance("DES"); SecretKey desKey = skf.generateSecret(dks); Cipher cipher = Cipher.getInstance("DES"); // DES/ECB/PKCS5Padding for SunJCE cipher.init(Cipher.ENCRYPT_MODE, desKey); CipherInputStream cis = new CipherInputStream(is, cipher); doCopy(cis, os); File file2 = new File("tempfile.class"); File f = new File("somefile.class"); f.delete(); file2.renameTo(f); } 

Now it works, but these deleting and renaming thing doesn't look elegant, how can I do it more efficient?