I built a simple demo application in C# using a modular approach so it consists of one executable and a couple of DLLs. Suppose I put it in a zip file and hand it over to somebody, with the sole purpose they can try out the demo application simply by extracting the file and doubleclicking the exe.
Now, to my understanding everybody that gets the application and the DLLs, can just add a reference to the DLLs in a Visual Studio project, and then start using whatever functions/classes they have as long as they are declared public. And hence, they can get access to a lot more than what I want them to access.
Is there a way to disable this, and get a system that is somehwat like with C++ DLLs (e.g. I can give anyone a lot of C++ DLLs and they'll have a rather hard time using the functions/classes in it if they do not have the header files)? Can I somehow strip the DLLs so that they are still usable by the exe, but do not expose references? Or are there attributes or so that I can use in the code that say "this class is usable only be DLLs/exes built by me"?
You could use the InternalsVisibleToAttribute and not make anything public, but...
You're mistaken if you think that anything stops someone from using non-public classes from your DLL. An application with full-trust can access private and internal content no problem, or they can decompile and rebuild the DLL with everything public.
People will suggest obfuscation, but that doesn't do much more.
You should read this answer (and question, but mostly answer): C#: How to Make it Harder for Hacker/Cracker to Get Around or Bypass the Licensing Check?
One possible solution is to leave public only the method that is supposed to be called from the executable. Everything else could be private or internal. You could also obfuscate the assembly. But remember that no matter what you do, there is always the possibility of using Reflection to invoke any method inside the assembly. Of course if it is obfuscated it will be a little harder but not impossible.
I think you can use Friend assemblies for that.
You may also obfuscate internals of your dlls so it become really hard to do reverse engineering and decompile your assemblies. Tools like Dotfuscator will rename all function/variable names inside your compiled dll to something like a0002345 so reading it will be really exhaustive.
Please notice that none of methods gives you 100% protection as still it is possible to use .NET reflection routines to access and use your private and internal classes. However making stuff internal or private will stop majority developers using those classes. Use obfuscation to stop advanced engineers who tries to dig into your compiled sources. In theory protection is considered safe enough if decompiling effort is greater than effort for writing similar tool from scratch. If somebody can't read your dlls the one won't be able to know how to use it.
No, sorry, not.
You could do ilmerge followed by obfuscation (I'm not sure what tool) for something similar.
Related
When we want to use a native shared library, we have to have the header files. So when we publish the software, others do not have the header files and they can not use the library.
But the managed library does not need any headers. Because you can simply use add reference in Visual Studio and use Object Browser to see all the classes and namespaces.
So when we publish our application with managed library, not only others can use our library in their own project (whether it is obfuscated or not), but also they can decompile it and see the whole source code if it is not obfuscated.
Is it true?
How can we secure our managed library?
Well, that's perfectly safe. In practice the main impact of having users able to see (a decompiled approximation of) the workings of the library is that you sometimes get a higher quality of bug report from them.
Software companies like Microsoft manage to eke a living despite consumers being able to decompile their libraries, or indeed just read the published source.
But if you really want to prevent it then being managed does not preclude being obfuscated.
There are several obfuscators available, and if you really want to get in the way of your users, you can ilmerge in the library to a make a single obfuscated executable, so they can't even use the library, never mind give you useful feedback copy your code.
Good day,
I want to take an existing C# project and wrap functions into a C++/CLI DLL. I need to be able to read this DLL from VB 6. I choose this route because I won't have to register a .net DLL in order to use it with VB 6. Frankly I have no experience with this kind of thing so I would greatly appreciate a good example. I know there are plenty of similar questions like this but I haven't been able to find anything simple enough for me to understand.
This is a fairly unwise route to pursue, making C# code [ComVisible] is pretty trivial and Regasm.exe should not scare you. The usual mistake with Regasm is to forget to use its /codebase option on your dev machine.
If you insist on not taking advantage of this then you'll need to find a way to get the CLR loaded yourself so it can execute your C++/CLI and C# code. There are three basic ways to do so. You've written off COM interop and hosting the CLR yourself isn't very practical if the host app is VB6. You however can take advantage of the C++/CLI compiler's ability to generate unmanaged DLL entrypoint stubs that load the CLR for you and switches to managed code execution. Do so by writing a static function that you decorate with __declspec(dllexport). The technique is shown in this answer. Beware that it isn't particularly performant and you'll have to live with the restrictions imposed by the VB6 Declare statement.
Also check this post-processing tool that can inject these stubs directly into a C# assembly. Not sure how reliable it is, I haven't used it myself.
Be a man and make that DLL under a couple of different compilation/linking/function-call-protocol configurations. Then go ahead and try a couple of different referencing configurations in your VB6 project. Post what works. Contribute, go forth!
Take a look at Export Managed Code as Unmanaged
and C# Project Template for Unmanaged Exports
It's a standard practice to decompile and reverse engineer .net assemblies.
I'd like to release some plugin assemblies that will add to existing applications, but I don't want them to be utilized by others.
What are some ways I can hide the source of these assemblies?
It's theoretically impossible to achieve 100% protection unless you control the target hardware. If the CPU is able to execute it, given enough time and knowledge, a human being can read it too. This is not even limited to C# (although it's usually easier to do in managed languages). You can use an obfuscator like Dotfuscator or XenoCode to make it harder to understand the decompiled code. If you're really concerned, you should move to a server-based application.
You can use an obfuscator tool, it will help but reverse engineering will still be very possible.
Your users' computer needs to know what it needs to do, so you have to tell it. The owner of the computer has total control over it, and can therefore know himself what you told the computer to do, and he can tell it to do something else.
There is a way to hide the data, its called steganography. There's an author of a number of articles covered on CodeProject, who wrote a framework for doing exactly this. The title of the articles were 'Steganography ' in a series from 1 up to 12 I think. This is the website that is affiliated with the author.
There is a also a obfuscator called 'Phoenix Protector', found here, which can obfuscate the .NET code, personally, I have not tried it but it sounds good.
Hope this helps,
Best regards,
Tom.
It's software; anything is possible. You can encrypt your binaries, and then decrypt all or part of them into your application at runtime. It's not foolproof, but it's up to you to decide how draconian you want to be.
You can write an app that will host CLR using the CLR COM api, that way you can first load and decode the assembly at the native code level. If you reinforce the native loader using several anti-reverse engeneering techniques, you can achieve good enough security.
At the very least, you should obfuscate your dlls to prevent hackers & competitors from viewing and making sense of your code. Obfuscation is not 100% foolproof, but it presents a big enough obstacle in their path.
Some obfuscators such as Crypto Obfuscator have a feature of embedding all dlls in the main exe so your dlls are not explicitly visible and available on disk to open in reverse-engineering tools such as Reflector.
Is it possible to make it so that my application cannot be used as a reference in other visual c# projects? My application was built using Visual C#, if you needed to know. Thanks!
You can't simply disallow another application from referencing your DLLs.
If you wanted to make it harder to use though, you could make all your methods and classes private or internal. If you have assemblies that need to reference it, you can make them friend assemblies, which would give them access to your internals. You could also take a look at obfuscating your code using these free .NET obfuscators.
There's no way to prevent others from using you assemblies if they can get they hands on them somehow. Obfuscation will make it harder (but not impossible) to reverse engineer the code, but if they just want to rip of your functionality even obfuscation isn't going to cut it. Using access modifiers will prevent others from using your code directly, but they can still access and call methods through reflection.
With that being said, you should probably also keep in mind that unless your assemblies can predict tomorrows stock prices the risk of someone actually using them without your permission may not be as big as you think. There are a lot of free libraries out there, so why would anyone go through the trouble of using your assemblies if they can get something similar for free?
HI,
Is there a way to prevent a particular dll in C# being opened in reflector. I can open many of the dll's and can get the code using reflector. But when trying to open some dll's it shows an error message stating that "The particual dll does not contain a CLI header.".
How can I make a dll like this??
Are you sure that these DLLs are managed-code-dlls? I don't think so, if they don't contain the CLI header, they aren't written in C#.
And for your question, you can't prevent a managed-DLL from being opened in a decompiler, all what you can do is to obfuscate it.
If you want to protect your .net dll you could obfuscate your assembly
Free .NET Obfuscation Tools
You have commercial ones too...
"The particual dll does not contain a CLI header.". message appears in Reflector because they are not managed dlls (.net).
I thought there was once a certain IL code which caused a crash in the reflector. But this bug is fixed now.
Obfuscation is nice - You can also try to encrypt certain critical parts of your code and decrypt+load+compile it at runtime. The problem is how to store the password.
You can't prevent it from being opened by the reflector.
There is no way to prevent Reflector from opening .Net assemblies, but you make make it pointless by obfuscating your assemblies. After obfuscating, class/method/fields are renamed, inline strings in methods are encrypted, method calls are hidden, method control flow is scrambled and so on. So, anybody who use Reflector will see a lot of garbage and will not be able to make sense of most of it.
DISCLAIMER: I work for LogicNP Software, the developers of Crypto Obfuscator