How can I limit the loading and execution of my libraries based on a defined precondition? For example, if I distribute to a client an application that uses an external library, how can I ensure the external library is only used with the application and not used by the client for other purposes?
Is code access security the answer? If so, is there a good example of how to apply it in the situation described above?
Thanks!
UPDATE: I cannot use services to protect the logic. I must supply the code in an assembly, and want to protect it from being used to build other products.
The best way to limit access is to move the logic from an assembly into a service layer. If you are truly concerned about protecting the logic in that assembly this is the best way.
Remember, any mechanism can be defeated with enough effort if the client has the assembly in their hands and is truly motivated to use it. That is why a service layer is a perfect solution as it gives your application access to the logic without allowing the client to obtain the implementation itself.
You should look into code obfuscation Nothing that you do will prevent someone dedicated enough from using the logic contained in your assembly however they see fit, however obfuscation will make it a more difficult and will hopefully deter most people.
See this question for more information
There's a build option to only allow friendly assemblies to use yours but that implies you can sign both your assembly and your client's as well. I doubt what you want to do is possible witout some sort of service layer or authentication/connection limitation to a server logic. Sorry.
Just a thought here and definitely this is not the safest or best way. Maybe just a small work around.
Instead of sending the assembly with the executable, how about moving the assembly to the Global Assembly Cache (GAC) and modifying the executable code to access the assembly present in the GAC? You can then change the name of the assembly to some garbage name (or whatever you think suitable) which the client will not be able to understand. So finding your assembly in that forest of assemblies would be almost impossible.
Hope this helps!
Regards,
Samar
Related
How do I protect the dlls of my project in such a way that they cannot be referenced and used by other people?
Thanks
The short answer is that beyond the obvious things, there is not much you can do.
The obvious things that you might want to consider (roughly in order of increasing difficulty and decreasing plausibility) include:
Static link so there is no DLL to attack.
Strip all symbols.
Use a .DEF file and an import library to have only anonymous exports known only by their export ids.
Keep the DLL in a resource and expose it in the file system (under a suitably obscure name, perhaps even generated at run time) only when running.
Hide all real functions behind a factory method that exchanges a secret (better, proof of knowledge of a secret) for a table of function pointers to the real methods.
Use anti-debugging techniques borrowed from the malware world to prevent reverse engineering. (Note that this will likely get you false positives from AV tools.)
Regardless, a sufficiently determined user can still figure out ways to use it. A decent disassembler will quickly provide all the information needed.
Note that if your DLL is really a COM object, or worse yet a CLR Assembly, then there is a huge amount of runtime type information that you can't strip off without breaking its intended use.
EDIT: Since you've retagged to imply that C# and .NET are the environment rather than a pure Win32 DLL written in C, then I really should revise the above to "You Can't, But..."
There has been a market for obfuscation tools for a long time to deal with environments where delivery of compilable source is mandatory, but you don't want to deliver useful source. There are C# products that play in that market, and it looks like at least one has chimed in.
Because loading an Assembly requires so much effort from the framework, it is likely that there are permission bits that exert some control for honest providers and consumers of Assemblies. I have not seen any discussion of the real security provided by these methods and simply don't know how effective they are against a determined attack.
A lot is going to depend on your use case. If you merely want to prevent casual use, you can probably find a solution that works for you. If you want to protect valuable trade secrets from reverse engineering and reuse, you may not be so happy.
You're facing the same issue as proponents of DRM.
If your program (which you wish to be able to run the DLL) is runnable by some user account, then there is nothing that can stop a sufficiently determined programmer who can log on as that user from isolating the code that performs the decryption and using that to decrypt your DLL and run it.
You can of course make it inconvenient to perform this reverse engineering, and that may well be enough.
Take a look at the StrongNameIdentityPermissionAttribute. It will allow you to declare access to your assembly. Combined with a good code protection tool (like CodeVeil (disclaimer I sell CodeVeil)) you'll be quite happy.
You could embed it into your executable, and extract and loadlibrary at runtime and call into it. Or you could use some kind of shared key to encrypt/decrypt the accompanying file and do the same above.
I'm assuming you've already considered solutions like compiling it in if you really don't want it shared. If someone really wants to get to it though, there are many ways to do it.
Have you tried .Net reactor? I recently came across it. Some people say its great but I am still testing it out.
Well you could mark all of your "public" classes as "internal" or "protected internal" then mark you assemblies with [assembly:InternalsVisibleTo("")] Attribute and no one but the marked assemblies can see the contents.
You may be interested in the following information about Friend assemblies:
http://msdn.microsoft.com/en-us/library/0tke9fxk(VS.80).aspx
I'm building a project that will support loading in external, managed DLLs, essentially as a modding system. However due to security reasons I'd like to restrict (as far as possible) what those external DLLs can access and do because they won't be made by myself.
My current plan was to simply blanket ban every assembly besides a select whitelist which I can add to upon request, however my main issue is the System.dll. It's probably the most important one to restrict access to due to the obvious reason that it can access System, however it also has vital namespaces like System.Collections, so it needs to be useable.
Is there a way to check specifically what assemblies and namespaces a loaded DLL is utilising or am I going about this the wrong way?
I've inherited an enormous .NET solution of about 200 projects. There are now some developers who wish to start adding their own components into our application, which will require that we begin exposing functionality via an API.
The major problem with that, of course, is that the solution we've got on our hands contains such a spider web of dependencies that we have to be careful to avoid sabotaging the API every time there's a minor change somewhere in the app. We'd also like to be able to incrementally expose new functionality without destroying any previous third party apps.
I have a way to solve this problem, but i'm not sure it's the ideal way - i was looking for other ideas.
My plan would be to essentially have three dlls.
APIServer_1_0.dll - this would be the dll with all of the dependencies.
APIClient_1_0.dll - this would be the dll our developers would actual refer to. No references to any of the mess in our solution.
APISupport_1_0.dll - this would contain the interfaces which would allow the client piece to dynamically load the "server" component and perform whatever functions are required. Both of the above dlls would depend upon this. It would be the only dll that the "client" piece refers to.
I initially arrived at this design, because the way in which we do inter process communication between windows services is sort of similar (except that the client talks to the server via named pipes, rather than dynamically loading dlls).
While i'm fairly certain i can make this work, i'm curious to know if there are better ways to accomplish the same task.
You may wish to take a look at Microsoft Managed Add-in Framework [MAF] and Managed Extensibiility Framework [MEF] (links courtesy of Kent Boogaart). As Kent states, the former is concerned with isolation of components, and the latter is primarily concerned with extensibility.
In the end, even if you do not leverage either, some of the concepts regarding API versioning are very useful - ie versioning interfaces, and then providing inter-version support through adapters.
Perhaps a little overkill, but definitely worth a look!
Hope this helps! :)
Why not just use the Assembly versioning built into .NET?
When you add a reference to an assembly, just be sure to check the 'Require specific version' checkbox on the reference. That way you know exactly which version of the Assembly you are using at any given time.
I want to secure my assembly (dll) by binding it to a specific environment. Say I have a dll (BizLogic.dll), I want to make it available to my co-developers to use it within the organization. But I don't want others to use it outside my organization.
Is there any way to address this issue?
Thanks in Advance.
--
Mohammed.
What you're describing is not the problem that CAS was designed to solve. The .NET Code Access Security system was designed to protect benign users from hostile third party code. You are trying to do the opposite -- protect benign code from hostile users. If you give someone a hunk of code, they can do whatever they want to that code -- disassemble it, rewrite it, recompile it, whatever, and there's not much you can do technically to stop them.
Probably your best bet is to use other enforcement mechanisms, like make them sign a contract that says that they will not reverse-engineer or redistribute your code, and then sue them if they do. Or, simply don't give them the code in the first place. Make a web service and keep the code on your server, away from the people you don't trust.
What do you mean by outside your organization?
Nevertheless, did you consider signing your assembly?
Very little that will be actually effective. You can try the various license/key frameworks that are out there, but there are exactly zero that are 100% uncrackable.
Create a domain user, give that user the only read permissions to a db object.
Set password never expires.
Physically secure the password.
dll must be able to access (via your new user) db object to proceed.
Obfuscate your code.
What recommendations can you give for a system which must do the following:
Load Plugins (and eventually execute them) but have 2 methods of loading these plugins:
Load only authorized plugins
(developed by the owner of the
software)
Load all plugins
And we need to be reasonably secure that the authorized plugins are the real deal (unmodified). However all plugins must be in seperate assemblies. I've been looking at using strong named assemblies for the plugins, with the public key stored in the loader application, but to me this seems too easy to modify the public key within the loader application (if the user was so inclined) regardless of any obfuscation of the loader application. Any more secure ideas?
Basically, if you're putting your code on someone else's machine, there's no absolute guarantee of security.
You can look at all kinds of security tricks, but in the end, the code is on their machine so it's out of your control.
How much do you stand to lose if the end user loads an unauthorised plugin?
How much do you stand to lose if the end user loads an unauthorised plugin?
Admittedly this won't happen often, but when/if it does happen we lose a lot and I although I understand we will produce nothing 100% secure, I want to make it enough of a hindrance to put people off doing it.
The annoying thing about going with a simple dynamic loading with full strong name, is that all it takes is a simple string literal change within the loader app to load any other assembly even though the plugins are signed.
you can broaden your question : "how can I protect my .net assemblies from reverse engineering ?"
the answer is - you can not. for those who havent seen it yet, just look up "reflector", and run it on some naive exe.
(by the way, this is always the answer for code that is out of your hands, as long as you do not have en/decryption hardware sent with it),
obfuscating tries to make the reverse engineering to be harder (cost more money) than development, and for some types of algorithems it succeeds.
Sign the assemblies.
Strong-name signing, or strong-naming,
gives a software component a globally
unique identity that cannot be spoofed
by someone else. Strong names are used
to guarantee that component
dependencies and configuration
statements map to exactly the right
component and component version.
http://msdn.microsoft.com/en-us/library/h4fa028b(VS.80).aspx