Building Encrypted Class Files

I would like to know if a Java file can be compiled in such a way that it can't be decompiled? Using a decompiler, any Java Class file can be decompiled, thus revealing the source code. But I have seen some Java Class files that when decompiled, gives encoded characters, instead of the text. So, the source code cannot be seen, but can be executed. How is this achieved? Is there some way to encrypt the class file, and still keep it executable?
Thanks,
TechnoSam

Use a code obfuscator. This makes it harder to read, but
it can still be decompilet. Since Java is compiled into
bytecodes, all you need to do is translate the bytecodes
back into source code in order to see the "source".
When you get right down to it, any program written
in any language can be decompiled. Microsoft used to
ship a program named 'debug' with DOS. This program
allowed you to decompile .exe files.
Mark

Similar Messages

Encrypting class files

Does anyone know if its possible to encrypt your compiled class files?
Purely for the reasons to stop people using tools to decompile your class files before they have paid for them etc..
Cheers

Yes. Just use any encryption program, like PGP.
The problem is of course that the JVM won't be able to decrypt it, so that is kind of pointless. :)
What you are looking for is not encryption, but obfuscation. Yes, there are programs out there that will change your bytecode in order to
a) Make it harder for decompilers to decompile it
and/or
b) Make it harder for humans to understand what is going on if someone still manages to decompile the bytecode.
Once upon a time I used a program called "SourceGuard" or something like that for this. I have later seen other programs mentioned in discussions about this, like "Zelix Klassmaster" http://www.zelix.com/klassmaster/
None of these tools should be expected to be absolutely safe, but they will make it so much harder that most people probably won't care to do the decompilation.
There is also a risk that the changes done with the bytecode will make the code unrunnable by some VMs.

Error when trying to build to .class files

i dont know if i am even doing it right, but here goes
I use
java -classpath "c:\path to source";"c:\path to source\jakarta-regexp-1.2.jar" -g -d .. *.java
when i launch i get
unrecongnized option: -g
could not create the java virtual machine.
anyone have a idea that might be able to fix this?

Then add %CLASSPATH% to the classpath
javac -classpath "c:\path to source;c:\path to
source\jakarta-regexp-1.2.jar;%CLASSPATH%" -g -d .. *.java

Is it possible to get a count of all the class files in a Flash Builder project?

Is it possible to get a count of all the class files in a Flash Builder project?
Thanks!

Resultsets are one per connection unless you have copied them. Do you have lots of connections are you properly reusing them or at least closing and discarding all references?
See tutorial and Javadoc of API too

Xcode 3/Interface Builder - Adding classes to NIB file doesn't work

I'm attempting to learn Objective-C and Cocoa GUI through Apple's "Currency Convertor" tutorial. I'm currently at the "Add the ConverterController Class to Your Nib File" step, and I add ConverterController.h to the Interface Builder project (both by Read Class Files and dragging) and... nothing happens. The tutorial clearly states that the class should appear as a new icon in the MainMenu.nib window. I've tried researching this problem, and it appears to be quite common, however every fix isn't really a fix at all. They all involve using the Identity Inspector for something, which appears very complicated, and is otherwise uncovered in the tutorial. It occurs to me that anyone knowing enough to be able to use this fix wouldn't be reading this tutorial, thus making such answers moot. Any help anyone could provide on this issue would be appreciated.

The tutorial you linked to should work fine except that they've just got the illustration (Figure 5-3) in the wrong place.
The placement of that illustration implies that you should see the instance of your class in the MainMenu.nib window right after doing step 2 (where you read your class file). But that's not really true. In reality it's step 3 that gets you the blue box in the MainMenu.nib window and steps 4 and 5 that will transform it from an "Object" into a "ConverterController". Steps 3, 4 and 5 are exactly what Thomvis suggested that you do earlier.
Steve

Advice on encrypting the class files so that it cannot be reverse engineer

Hi,
i will like to ask if there is any way where we can encrypt the class files so that people cannot use reverse engineering to modify the codes?
Thanks

tommickey wrote:
leeChaolan wrote:
Hi,
i will like to ask if there is any way where we can encrypt the class files so that people cannot use reverse engineering to modify the codes?
ThanksIn addition to what others said encryption is totally different from what you want.(called as 'obfuscation').Not necessarily. You could encrypt the class files, but then you would have to provide an unencrypted ClassLoader (and possibly Main if you didn't want to put the ClassLoader in the bootstrap classpath) that is capable of decrypting them. Then, someone could decompile this ClassLoader (obfuscated or not) and either simply take the decryption algorithm and decrypt the classes, or even easier, simply modify the ClassLoader to write out the decrypted class files itself.
So, why would you? ;-)

Class file build date printout

I want the class file build date printed out when I run one of my servlets, using the log(...) method. How can I retrieve the servlet class file build date so that I can log it when the servlet starts up please?
Thanks a lot!
Charl

Hi everybody!
I've got a problem like this. I've got some file which can be modified and i want the date where the file was created not the date where it was modified. How i can do this ?
thanks for the reply.
Excuse-me, my english isn't perfect

Adding .class files to your project and making them work.

Ok, im fairly new to java and having trouble understanding how to make importing of .class files work. Im using eclipse 3.2
I have the files in a directory and I have gone to project->properties->java build path->libraries->add external class folder and pointed it to the correct place.
Now, I am trying to use some of the classes it provides. I get no errors when creating the object with this code:
com.ECS.client.jax.ItemSearchRequest itemRequest = new com.ECS.client.jax.ItemSearchRequest();
Before I did the add external class folder that code would error cause it didnt know what com.ECS was. Now it works fine. My problem is that when I try to use a class, it does not recognize it as a class. After doing the above code I have:
itemRequest.setSearchIndex("Books");
its giving me an error on the period, saying: "Syntax error on token(s), misplaced construct(s)". Its not seeing that it is a class, so I can't use it. But when I am creating the object I get no errors. For reference, here is the chunk of code:
com.ECS.client.jax.ItemSearchRequest itemRequest = new com.ECS.client.jax.ItemSearchRequest();
itemRequest.setSearchIndex("Books");
the second line of which errors. So my question is, how do I get it to recognize that the itemRequest is a class when I have imported the .class files to my project already?

It's working fine. It's just that you have to put your code in a method.

How to convert class file into exe

I have made a simple calculator using swing.now i want it to be used as an application from the desktop..How can i do it?..any suggestions?

raghu0007 wrote:
I have converted the class file to jar using jar cvf simplecalci.jar simplecalci.class.
Now i don't know wat to do next since when i double click the jar.....windows shows the message
Failed to load Main-class manifest attribute from c:\users\raghu\simplecalculator\build\classes\simplecalculator\simplecalci.jar
I am using netbeans and i have JRE 5 as well as JRE 6 installed.
I don't knw wat to do.Netbeans creates the .jar file for you,
Simply right click on the project node in nb and select
clean and buildnext goto the location of the project
Eg:
C:\Documents and Settings\raghu0007\My Documents\NetBeans Projects\SimpleCalculcator\dist\There will usually be 2 files in there, 1 for the Gui parts and the other(.jar) the rest.
These two files must always be together (same directory for the jar file to work)
copy the dist folder to C:\Program Files\, Rename it and create a shortcut to the simplecalci.jar file
If you know the above just take a look at how you modified the MANAFEST file and the file(MF,class...) locations in the .jar
For Windows XP
Edited by: gtRpr on 2008/06/20 09:48

How do I make a batch file if the .class file uses a foreign package?

I am trying to make an MS-DOS batch file using the bytecode file from the Java source file, called AddFields.java. This program uses the package BreezySwing; which is not standard with the JDK. I had to download it seperately. I will come back to this batch file later.
But first, in order to prove the concept, I created a Java file called Soap.java in JCreator. It is a very simple GUI program that uses the javax.swing package; which does come with the JDK. The JDK is currently stored in the following directory: C:\Program Files\Java\jdk1.6.0_07. I have the PATH environment variable set to the 'bin' folder of the JDK. I believe that it is important that this variable stay this way because C:\Program Files\Java\jdk1.6.0_07\bin is where the file 'java.exe' and 'javac.exe' are stored. Here is my batch file so far for Soap:
@echo off
cd \acorn
set path=C:\Program Files\Java\jdk1.6.0_07\bin
set classpath=.
java Soap
pause
Before I ran this file, I compiled Soap.java in my IDE and then ran it successfully. Then I moved the .class file to the directory C:\acorn. I put NOTHING ELSE in this folder. then I told the computer where to find the file 'java.exe' which I know is needed for execution of the .class file. I put the above text in Notepad and then saved it as Soap.bat onto my desktop. When I double click on it, the command prompt comes up in a little green box for a few seconds, and then the GUI opens and says "It Works!". Now that I know the concept of batch files, I tried creating another one that used the BreezySwing package.
After I installed my JDK, I installed BreezySwing and TerminalIO which are two foreign packages that make building code much easier. I downloaded the .zip file from Lambert and Osborne called BreezySwingAndTerminalIO.zip. I extracted the files to the 'bin' folder of my JDK. Once I did this, and set the PATH environment variable to the 'bin' folder of my JDK, all BreezySwing and TerminalIO programs that I made worked. Now I wanted to make a batch file from the program AddFields.java. It is a GUI program that imports two packages, the traditional GUI javax.swing package and the foreign package BreezySwing. The user enters two numbers in two DoubleField objects and then selects one of four buttons; one for each arithmetic operation (add, subtract, multiply, or divide). Then the program displays the solution in a third DoubleField object. This program both compiles and runs successfully in JCreator. So, next I moved the .class file from the MyProjects folder that JCreator uses to C:\acorn. I put nothing else in this folder. The file Soap.class was still in there, but I did not think it would matter. Then I created the batch file:
@echo off
cd \acorn
set path=C:\Program Files\Java\jdk1.6.0_07\bin
set classpath=.
java AddFields
pause
As you can see, it is exactly the same as the one for Soap. I made this file in Notepad and called it AddFields.bat. Upon double clicking on the file, I got this error message from command prompt:
Exception in thread "main" java.lang.NoClassDefFoundError: BreezySwing/GBFrame
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:12
4)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
Caused by: java.lang.ClassNotFoundException: BreezySwing.GBFrame
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
... 12 more
Press any key to continue . . .
I know that most of this makes no sense; but that it only means that it cannot find the class BreezySwing or GBFrame (which AddFields extends). Notice, however that it does not give an error for javax.swing. If I change the "set path..." command to anything other than the 'bin' folder of my JDK, I get this error:
'java' is not recognized as an internal or external command,
operable program or batch file.
Press any key to continue . . .
I know this means that the computer cannot find the file 'java.exe' which I believe holds all of the java.x.y.z style packages (native packages); but not BreezySwing or any other foreign packages. Remember, I do not get this error for any of the native Java packages. I decided to compare the java.x.y.z packages with BreezySwing:
I see that all of the native packages are not actually visible in the JDK's bin folder. I think that they are all stored in one of the .exe files in there because there are no .class files in the JDK's bin folder.
However, BreezySwing is different, there is no such file called "BreezySwing.exe"; there are just about 20 .class files all with names like "GBFrame.class", and "GBActionListener.class". As a last effort, I moved all of these .class files directly into the bin folder (they were originally in a seperate folder called BreezySwingAndTerminalIO). This did nothing; even with all of the files in the same folder as java.exe.
So my question is: What do I need to do to get the BreezySwing package recognized on my computer? Is there possibly a download for a file called "BreezySwing.exe" somewhere that would be similar to "java.exe" and contain all of the BreezySwing packages?

There is a lot of detail in your posts. I won't properly quote everything you put (too laborious). Instead I'll just put your words inside quotes (").
"..there are some things about the interface that I do not like."
Like +what?+ This is not a help desk, and I would appreciate you participating in this discussion by providing details of what it is about the 'interface' of webstart that you 'do not like'. They are probably misunderstandings on your part.
"Some of the .jar files I made were so dangerously corrupt, that I had to restart my computer before I could delete them."
Corrupt?! I have never once had the Java tools produce a corrupt Jar. OTOH, the 'cannot delete' problem might relate to the JRE gaining a file lock on the archive at run-time. If the file lock persisted after ending the app., it suggests that the JRE was not properly shut down. This is a bug in the code and should be fixed. Deploying as .class files will only 'hide' the problem (from casual inspection - though the Task Manager should show the orphaned 'java' process).
"I then turned to batch files for their simple structure and portability (I managed to successfully transport a java.util containing batch file from my computer to another). This was what I did:
- I created a folder called Task
- Then I copied three things into this folder: 1. The file "java.exe" from my JDK. 2. The program's .class file (Count.class). and 3. The original batch file.
- Then I moved the folder from a removable disk to the second computer's C drive (C:\Task).
- Last, I changed the code in the batch file...:"
That is the +funniest+ thing I've heard on the forums in the last 72 hours. You say that is easy?! Some points.
- editing batch files is not scalable to 100+ machines, let alone 10000+.
- The fact that Java worked on the target machine was because it was +already installed.+ Dragging the 'java.exe' onto a Windows PC which has no Java will not magically make it 'Java enabled'.
And speaking of Java on the client machine. Webstart has in-built mechanisms to ensure that the end user has the minimum required Java version to run the app. - we can also use the [deployJava.js|http://java.sun.com/javase/6/docs/technotes/guides/jweb/deployment_advice.html#deplToolkit] on the original web page, to check for minimum Java before it puts the link to download/install the app. - if the user does not have the required Java, the script should guide them through installing it.
Those nice features in deployJava.js are available to applets and apps. launched using webstart, but they are not available for (plain) Jar's or loose class files. So if 'ensuring the user has Java' is one of the requirements for your launch, you are barking up the wrong tree by deploying loose class files.
Note also that if you abandon webstart, but have your app. set up to work from a Jar, the installation process would be similar to above (though it would not need a .bat file, or editing it). This basic strategy is one way that I provide [Appleteer (as a downloadable ZIP archive)|http://pscode.org/appleteer/#download]. Though I side-step your part 1 by putting the stuff into a Jar with the path Appleteer/ - when the user expands the ZIP, the parts of the app. are already in the Appleteer directory.
Appleteer is also provided as a webstart launched application (and as an applet). Either of those are 'easier' to use than the downloadable ZIP, but I thought I would provide it in case the end user wants to save it to disk and transport the app. to a machine with no internet connection, but with Java (why they would be testing applets on a PC with no internet connection, I am not sure - but the option is there).
"I know that .jar and .exe files are out because I always get errors and I do not like their interfaces. "
What on earth are you talking about? Once the app. is on-screen, the end user would not be able to distinguish between
1) A Jar launched using a manifest.
2) A Jar launched using webstart.
3) Loose class files.
Your fixation on .bat files sounds much like the adage that 'If the only tool you have is a hammer, every job starts to look like a nail'.
Get over them, will you? +Using .bat files is not a practical way to provide a Java app. to the end user+ (and launching an app. from a .bat looks quite crappy and 'second hand' to +this+ user).
Edit 1:
The instructions for running Appleteer as a Jar are further up the page, in the [Running Appleteer: Application|http://pscode.org/appleteer/#application] section.
Edited by: AndrewThompson64 on May 19, 2009 12:06 PM

How to build a jar file so the program can access its resources folder?

I have a java program written by someone else in which I have made a trivial change (I changed the background color). The jar file runs but it does not find one of the resources file.
Here is the project folder's structure
mainClass.txt (manifest text file)
folder resources (includes file Java does not find: order.txt, a text file)
folder CFPT ( includes .class files)
folder cpl (includes .class files)
folder results
I tried
jar cvmf mainClass.txt CFPT0.jar CFPT/*.class cpl/*.class resources results
I get a lot of "adding: resources/..."
including the one pertaining to the files which is later not found
adding: resources/order.txt(in = 411) (out= 169)(deflated 58%)
the code that chokes right now is the following,
Object i = new Object();
InputStream is = i.getClass().getResourceAsStream("/resources/" + resourceName);
when I run java -jar CFPT0.jar the program runs
but it soon gives an error, cannot find resourceName order.txt (is == null)
I have Core Java Volume 1 page 498 but it does not help me figure out what I am doing wrong.
Can somone help me build the jar file correctly so the program can find its resources?
Is this a classpath issue? What do I need to do?

My last mainClass.txt file content:
Main-Class: CFPT.CFPTRunner
Class-Path: ./resources ./results
I also tried
Class-Path: resources results
Initially I only had the first line.
I put back /resources in the java file as the / is necessary to indicate absolute path.
Otherwise it looks relative to calling class.
I tried adding the path on the second line of the manifest file per Wikipedia example
http://en.wikipedia.org/wiki/Classpath
I looked at
http://java.sun.com/javase/6/docs/technotes/guides/lang/resources.html
If you use the -sourcepath option, the compiler searches the indicated path for source files; otherwise the compiler searches the user class path both for class files and source files.
http://java.sun.com/javase/6/docs/technotes/guides/lang/resources.html
resources
I took out the -d classes and compiled the .class files right with the java files in case that was the problem
javac -classpath . CFPT/CFPTRunner.java
jar cvmf mainClass.txt CFPT0.jar CFPT/*.class cpl/*.class resources results
java -jar CFPT0.jar
Still no go

Converting Java class file to .dll

Dear all,
Is there any way to convert a Java class file to a .dll file?
(Background being that there is a software that only allows callouts to DLLs and the method I have developed is in Java so need to convert it to a .dll)
Any insight/advice/pointers are most appreciated.
Thanks much,
David

Hi there,
Yes you can convert a Java Class to DLL file using Microsoft Visual J#.NET (Installation required Visual Studio.NET) you can download it from the microsoft site.
www.microsoft.com/downloads
then go for search below in combo box(Visual J#.NET). After installation open new project select class library. write your java code(not fully supported j2se). build your application. All the Java Code is embeded in dll. Found at e.g. C:/JavaToDll/bin/debug/JavaToDll.dll This is a way to convert Java Code to a dll. frankly speaking i do not like .NET (copy of Java Technology must be baned completely).
Thanks
Please correct if i am wrong.
Yahya Kamran (Software Engineer)

How to save library symbols' class files in packages that are not the default package?

Hi,
I perform the following in Flash CS5 with Flash Builder 4
1) Create a new library symbol.
2) Do a RightClick->Properties on the new symbol
3) Check the options for "Export for ActionScript" and "Export in frame 1".
4) I write a new name for my class "Class1" and click on the pencil icon "edit class definition" to edit the class.
At this point my FlashBuilder 4 takes over and opens the "New ActionScript" dialog.
4) I then click on Package-Browse to select a package e.g. com.mycompany.myfiles as the new class destination.
The as file is created as com.mycompany.myfiles/Class1.as as everything seems just fine.
5) I close the ActionScript file and back in Flash CS5 I RightClick on the symbol and select "Edit Class".
At this time, FB4 suggests again to create the file, ignoring the fact that I already created it before.
Do you know of a way I can make Flash CS5 remember where I created the file?
Thanks.

Hi,
I didn't remove the project or delete any of the files.
All I did was create the class file under a package that is not the default package. Then when I clicked on the Flash symbol's "Edit Class" It asked me again to create the same class file.
Only if I create the class in the default package, it won't ask me to recreate it again.
Bye,
RaamEE-IL

Class file location

I am not sure if this would be an admin type question but
here goes:
I have a Coldfusion 6.1 server riding on Weblogic 8 ish and I
am trying to do a small java example... *sigh*
I am getting a "class not found" error and so I went looking
for my classpath, since it didn't seem to be what was default in
the documentation. *sigh*
So I find that it is defaulting to .jar files and no
directories. I can see that there are class files that are out in
our coldfusion land so how does it see these? I am pretty ignorant
of weblogic. I was curious how they can be reading the files, if
they are, when the paths that I see only point to jar files. So, no
explanation is too simple, please use small words and type slow for
me. How should/do I change the path since I have to change it in
Weblogic not CF admin. Is there some kind of default folder I am
missing? I even tried adding my class to cfclasses under the cf
file directory. Any help (and I need a lot) would be greatly
appreciated.
Thank you in advance for your infinite patience and any help
you can provide!!!
~Va :-)

I f you want to try the jar method, here's a quicky on how to
jar up your file as a package.
in a work folder, create a folder structure for your package,
convention uses reverse internet domain (i.e.
com.adobe.packagename)
for this one, we'll use a simple one level package called
ironyx. So create a folder called ironyx.
copy the java file you want to package up into the ironyx
folder
at the top of the java file place the following;
package ironyx;
Compile the java file.
Using a command prompt in the parent folder of the ironyx
folder, type the following;
jar -cf ironyx.jar ironyx
This will jar up the ironyx folder contents, including both
the java and class files into an ironyx.jar file. You can delete
the source java files prior to creation of the jar file if you
wish.
Copy the jar file to ColdFusion WEB-INF\lib directory, bounce
the cf instance
A typical cf execution might look like
<cfset mySimpleMath=
CreateObject("java","ironyx.SimpleMath")>

<cfset mySimpleMath.init()>

<cfset result = mySimpleMath.addNumbers(num1, num2)>
Note: If you're using the SimpleMath class file from
http://builder.com.com/5100-6370-5177283.html,
they have a text formatting error for the method. There should be
spaces in publicintaddNumbers and it should look like
public int addNumbers

Java .class files low-level (hex) editing?

Hello, all!
I have a problem:
There is an application (namely a J2ME instant messanger for Nokia mobiles). It is a non-commercial application. But unfortunately, there is a bad bug in the application. It is not even a bug, it is more a feature - but it does not support Russian (cyrillic) characters encoding. Russian characters in all incoming messages are displayed with a kind of hierogliphs.
I wrote to developers (and not only I did - I know at least 3 russian people who also wrote a developer about this) - but unsuccessful. Developer keeps silent.
So what I decided is to fix the bug by myself :) By decompilation, e t.c.
Unfortunally, the midlet is hard obfuscated :( So it took me some hours of reading obfuscated code, and now I see some ways which I must try to solve the problem. I think I must write a code which processes the desired String variables (Despite obfuscation, I can see which Strings to process to obtain effect), and inject this code somewhere to be executed, and from where it could reach the desired Strings.
But the great problem is that obfuscated classes produce a lot of erroneus code, which can not be compiled back. So I decide to reject the decompilation at all, or at least of the big classes (where it is a lot of errors, which I can not correct manually).
In some moments, the application stores the desired Strings in the java.lang.Hashmap. So if I could place my processing code into the Hashmap methods, then I could easily process what I need.
Evidently, I can not edit the real basic java classes. But why not to make the applicaton using my class with identical functionality, instead of java.jang.Hashmap?
My idea now is to edit the .class file of the midlet (yeah, edit with notepad), replacing all the references to "java/lang/Hashmap" or "java.lang.Hasmap" with "java/lang/Fuckmap" and "java.lang.Fuckmap".
So did I (replaced it in norepad).
I read the Sun's documentation about .class file structure, and it seems that nothing is against it. There is no encryption, no checksums, e t.c.
Then I produced "Fuckmap" class this way:
import java.lang.Hashmap;
class Fuckmap extends Hashmap {}
(compiled and preverified it of course)
And placed it into java/lang folder inside the application jar.
I instead of working properly, I get the "Application error - invalid constant pool entry"). What do I do wrong?

2 lexzeus, mlk:
I understood you.
I jave just tried it, and used "jaga/util/Fuckmap" (jaga, not java). But still the same ("Invalid constant pool entry). I tried two times (maybe I could make something wrong?), both times took "clean" jar package, e t.c.
Do you really think jav.alang.Hashmap should help now? I have ony little hope :(

Building Encrypted Class Files

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