This can be possible duplicate of this question, but I don't want to go with solution suggested i.e. use of Web Service.
Here is the scenario:
1) I want to expose one class library to clients. Let's name it "MyClassLibrary".
2) There are two more libraries "Library1" and "Library2" in the same solution for "MyClassLibrary" project.
3) "Libray1" is referred in "Library2" and "Library2" is referred in "MyClassLibrary".
4) There is no direct reference of "Libray1" inside "MyClassLibrary".
What do I want?
Client of "MyClassLibrary" should not be able to access classes, methods in "Library1". Is it ever possible? If I create nuget package for "MyClassLibrary", it will contain dll for "Library1" (as well as "Library2"). So using that dll, client can easily access stuff in "Library1" (as well as in "Library2"). How can I avoid that? I want my client to be able to access only required functions from "MyClassLibrary" and not implementation of "Library1" (and maybe "Library2"). How to achieve this?
If you want to make it less convenient for your client to access your code, you could use access specifiers to prevent him from doing so. For example you could use the InternalsVisibleTo attribute to hide your implementation, or put it all in one single assembly and make most of it private.
However, this is just to prevent him from accidentally using it.
If it contains secrets that you don't want him to know, you must not deliver it to him. One option would be to only deliver the interface of a webservice and have the actual service with your secrets run at your location. If you give him the assemblies, no mater how well protected, obfuscated or otherwise obscured, your secret is in the open.
Nope. Making things internal solves the problem you just described. As well, be aware of existence of [assembly:InternalsVisibleTo(...)].
Surely, rightly applied reflection makes even private things accessible. But I don't consider such a case.
Related
I have a project where I want only one class to have access to a dll. I would be content with hiding the dll from intellisense, but still having access to it if that is an option. Either way, I want only one class to use the dll and for it not to be seen and/or accessible otherwise.
I'm using C# in visual studios.
Simply said: You can't do that (but keep reading).
Basically, a DLL (From the .NET perspective) is a bunch of code and config files. No more than that. So, given that you'll need to make public those classes in order to be used from another ones outside that assembly then you can not.
What you can do (I ended up doing this a few years ago) is to use some kind of reflection to determine which class (and namespace) is trying to access your assembly and only permit the proper one.
Other way is to implement a key negotiation between your DLL and the permitted assembly. You'll need to implement those manually, as far as I know.
Anyway, keep in mind there's always a way to bypass this kind of protection by disassembling and modifying your code. So, at least, don't forget to obfuscate the file. Anyway, this will just make it a little more painful, but still possible.
An alternate approach, if you goal is to stop people using the functionality of the dll by accident is to push your wrapper class into an intermediary assembly. Your project then references that intermediary project, rather than the underlying dll which effectively hides it. So your project structure would change to something like this:
Main Project -> references API Wrapper Project -> references API DLL
For this to work, your wrapper project needs to make sure that it doesn't accidentally expose any of the API DLL classes through its public interface.
Obviously this doesn't stop your developers from going in and adding a reference to the API DLL so that they can use the library directly, but if the goal is to stop accidental access to the API DLL classes because intellisense has helped the developer out a bit too much then it might be a viable option.
I want to restrict other application from using dll functions that I have written.
Eg.
If i hav database.dll containg two functions.
public void InsertInToDatabse();
public void ClearDatabase();
Now If my application has called InsertInToDatabse() and is doing some other work,till this time if some other application calls ClearDatabase() by referencing database.dll , The databse would be cler out.So how can I restrict calls to these functions form third party application ?
if your dll is a class library the actual configuration file will be the one of the client application (web.config or app.exe.config) and in there only authorized applications will have proper connection string with username, password, db server and db name.
Now, even if unauthorized apps would be prevented to call you dll's methods in the way you are looking for, in case those bad apps have direct access to the database by knowing the connection string, they can still mess around.
this would to say that in fact as long as the configuration is outside your dll you shouldn't worry because only authorized apps will be accessing the proper database.
if this approach still does not satisfy you, then you should be using security check like CAS which allows you to specify which class or assembly can be calling a certain method so even if your dll is referenced by another application it won't work. Beware that in .NET 4 (you tagged it in the question) the whole security layer has been changed and works differently from older .NET Framework versions, check this article for more details: http://msdn.microsoft.com/en-us/library/dd233103.aspx
You cannot stop people from calling your functions, but you are free to implement your functions to protect against such circumstances.
For instance, you could put a lock around database accesses so that the call blocks until the previous call has finished, or you could have a flag that causes the Clear() call to return immediately with an error code or exception.
EDIT: I may have misunderstood the question. If you NEVER want third party code to call your functions then use internal (and/or InternalsVisibleTo) as Marcus suggests.
You could use internal access on the methods you want to protect (instead of public), then mark your projects as Friend Assemblies. This is the same way you allow unit test projects to access internal methods.
Here's a description from MSDN's Friend Assemblies article...
Only assemblies that you explicitly specify as friends can access Friend (Visual Basic) or internal (C#) types and members. For example, if assembly B is a friend of assembly A and assembly C references assembly B, C does not have access to Friend (Visual Basic) or internal (C#) types in A.
As Marcus mentioned you could use the internal keyword. And then apply the InternalsVisibleToAttribute to your class library with the assemblyname of your application assembly and your public key if you are using strong assemblynames.
MSDN link
If you're asking about security:
Another technique would be to make the client pass in a parameter, such as a password or an encrypted connection string for example.
If you're asking about restriction by caching (eg. only allow this method to be called once every minute) - then look at either [AspNetCacheProfile] for services or Cache.Insert for application code.
If I remember correctly, the internal keyword is for exactly these types of situations.
Edit: As said in comments, if class A is in assembly B, then class C in assembly D won't have access to A.
Also, as pointed out in other answers, you can (and probably should) have some form of authentication in the ClearDatabase().
Edit 2: It just dawned on me that these sort of permissions should be on a database-level, which means that if the following user (with those privileges):
A: Insert, Update, Create
tried to Drop Table, then the application would throw an exception (or however you handle errors), which, obviously, would prevent them from just doing that.
This is not to say that you shouldn't set ClearDatabase() as internal, but if the user (the third-party is using) has permissions to Drop Table then s/he would be able to regardless.
Edit 3:
The problem is not how to secure your code, the problem is how to secure your database.
– Huusom
In C#, is it possible to restrict who can call a method at compile time?
I've looked into directives, but that didn't work since I can't assign values to symbols.
#define WHO VisualStudioUser.Current // does not work
I also looked into Code Access Security (CAS) but that's runtime enforcement, not compile time.
The requirement is to restrict access to a method at compile time for specific developers given the method exists in a pre-compiled assembly.
here's more details...
I'm building a framework or a series or assemblies for a team of developers. Because of our software license restrictions, I can only allow a few developers to write code to make a call to some restricted methods. The developers will not have access to the source code of the framework but they'll have access to the compiled framework assemblies.
The quick answer will be: No this isn't possible, and if you need to do it, you're Doing It Wrong.
How would this even work? Does it depend who who's running the code or who wrote it?
Edit There's kind of a way using InternalsVisibleTo and restricting accessing in source control to the assemblies that InternalsVisibleTo is specified for. See Jordão's answer
The requirement is to restrict access to a method at compile time for specific developers given the method exists in a pre-compiled assembly.
One way is to mark the method private or internal, it won't be callable by anyone outside the assembly. UPDATE: Also take a look at the InternalsVisibleTo attribute, which is used to define which assemblies can "see" internals of your assembly.
Another way is to divide the code you want to distribute from the code you don't want people to call into separate assemblies. Maybe you just share an assembly mostly of interfaces with your users, that they them compile against; and you have a separate assembly with implementations that they shouldn't reference directly. Your internal team would have access to the implementation assembly. This is just a common form of dependency management, the dependency inversion principle.
Draft:
Compile the restricted code into (obfuscated) DLLs: TypeA.dll, TypeB.dll etc.
Define an interface for each type, and compile them into separate DLLs: ITypeA.dll, ITypeB.dll etc.
Create a "guard assembly", and embed all restricted assemblies into it: Guard.dll. This has a ResolveEventHandler, and methods to instantiate different types defined in the embedded restricted DLLs. Instances are returned through their interface.
Developers get the interface DLLs and the Guard.dll. Each developer can get a Guard.dll with special authentication tokens in it. For example, a Guard.dll can be bound to PC, an IP address, a GUID issued to the developer, anything.
The developer can instantiate those types for which she has the proper authentication code, and uses the object instance through an interface.
Sorry this is a bit fuzzy, because it was more than a year ago when I used these techniques. I hope the main idea is clear.
Can you try using Extensible C# developed by ResolveCorp, some of the links for study and implementation are:
http://zef.me/782/extensible-c
http://www.codeproject.com/KB/architecture/DbCwithXCSharp.aspx
http://weblogs.asp.net/nunitaddin/archive/2003/02/14/2412.aspx
http://www.devx.com/dotnet/Article/11579/0/page/5
I have a group of dlls for WCF services. The contain contracts, interfaces etc. I would like to reuse this code in the API (client side) but don't want the consumers of the API to use these features.
Is there a way to say core.dll can only be used by clientcore.dll?
Well, you can give all the members of core.dll an access modifier of internal and then use InternalsVisibleToAttribute to give access to clientcore.dll.
To make life easier for your clients, you might actually want to merge core.dll into clientcore.dll using ILmerge. That way your callers don't need to copy a DLL they never use directly.
Yes, make your types internal and then use the friend assembly mechanism (via the InternalsVisibleToAttribute class).
sure, it's called:
Code Access Security
I'm allowing users of my application to run snippets of C# to be able to directly manipulate certain objects in my assemblies without me having to write a big scripting interface layer to explicitly expose everything.
This code will be injected into a dynamically compiled assembly, so I can control the assembly itself, but I need to stop the code accessing my private methods using reflection.
I tried calling securityPermissionObject.Deny() just before running the code, but this blocks methods on my objects from using reflection (which some do) when they are called by the user's code.
Is there a way to restrict the permissions only on the suspicious assembly without affecting the public methods it calls on my trusted assemblies?
Try to create a new appdomain. And use it as a sandbox. Within this sandbox you can load your assembly in.
Here is an example.
Of course because you now have two appdomains it complicates communictiaon a bit. You might consider a Webservice through a pipe or other communication mechanisms.
Here is an article of how two appdomains can communicate.
(An old question, not sure whether you still need an answer)
When calls are coming back into your public methods, then the first thing you need to do is carefully sanitize the parameters, and reject any bad calls. After that, you can add a call to Assert for RelectionPermission. This basically allows any code you call which requires reflection to be satisfied, and not see the Deny higher up in the call stack.