I want to prevent an assembly to be loaded from another application. So that it can be loaded from my application only.
Rigth now I'm using Assambly.LoadFrom to load the assembly.
Ultimately, no. It sounds like you are deploying a dll, but you want to retain sole control over how it is used. That is just an arms race; ultimately if somebody really, really wants to (ab)use it, they can. Even if that means disassembling, de-obfuscating, and disarming any preventative code you have added.
The only way to block that: don't give it to them. Consider using a web-service for some functions. Then they don't have the assembly.
You can try to validating entry assembly (Assembly.GetEntryAssembly) somewhere in your 'protected' assembly.
You can't stop people from using your DLL using technological approach. You can try to make it more difficult but a sufficiently skilled user will be able to modify the assembly so that they can use it.
You could try a legal approach. You can include a clause in your license agreement which disallows people from using your assembly in another application. But it won't stop everyone.
You could use the InternalsVisibleToAttribute in your assembly and specify your application assembly as a "friend". This will prevent other assemblies of using types provided they are marked as internal but will allow your application to still use those types.
From MSDN:
Ordinarily, types and members with
internal scope (in C#) and friend
scope (in Visual Basic) are visible
only in the assembly in which they are
defined. The
InternalsVisibleToAttribute attribute
makes them also visible to the types
in a specified assembly.
The attribute is applied at the
assembly level. This means that it can
be included at the beginning of a
source code file, or it can be
included in the AssemblyInfo file in a
Visual Studio project. You can use the
attribute to specify a single assembly
that can access the internal types and
members of the current assembly. To
make the assembly's internal types and
members visible to additional
assemblies, you must include a
separate InternalsVisibleToAttribute
attribute for each assembly.
Not that this does not prevent anyone from loading your assembly, it just prevents them from using the internal types within the assembly (at least not without some major effort, in the end anyone can just disassemble your code and use it that way).
Obfuscate it and keep documentation secret. Also include a key as in:
http://www.codeguru.com/columns/experts/article.php/c4643
Related
Let me clarify:
I have built a class library to be used in several projects. As part of this DLL I want to add a few different custom providers for Owin Cookies by extending CookieAuthenticationProvider so I need to include a reference to Microsoft.Owin.Security.Cookies. This is safe because the newer projects that will use my library also use Microsoft.Owin.Security.Cookies.
However some of the projects are older and dont use Owin etc... Will they blow up if I include the library for other use? Or will they only blow up if I try to use the provider (which I wouldn't since they cant use it).
I want to put some commonly used things in my library without having to reference every one of it's dependent DLL's to every project that uses them. I'm pretty sure what I'm doing is ok but I was hoping somone could tell me before I waste many hours going forward with this. Also if there is a better way I'm all ears.
The rules:
All types which are visible to a given assembly must be declared in assemblies referenced by that assembly.As long as your class library does not actually expose in its public API the types found in the Microsoft.Owin.Security.Cookies assembly, then other assemblies can safely compile with your DLL without referencing that assembly.
A referenced assembly need not be present at runtime, except when code in that assembly is actually needed, i.e. some other code attempts to call that code.
In general, this means that as long as other assemblies which are referencing your assembly and which don't reference Microsoft.Owin.Security.Cookies also don't call any code in your assembly that would then in turn attempt to call code in Microsoft.Owin.Security.Cookies, that assembly need not be present at runtime.
The tricky part on that second point is that what constitutes "calling code in Microsoft.Owin.Security.Cookies" is not always clear. Typically, as long as you don't access the types in the assembly at all, .NET won't try to execute any code in that assembly. But it's not hard to accidently access the types even when they are not necessarily needed (e.g. in initializers, static or otherwise, code that checks for interface implementations, etc.).
If you really want your clients to be able to use your DLL, which references Microsoft.Owin.Security.Cookies, without necessarily needing that DLL to be present at runtime, you will need to be very careful to ensure you've fully supported that scenario. It is possible to do, but it's also not hard to make a mistake.
(I have to admit, I'm surprised that this useful question hasn't already been addressed on Stack Overflow. Seems like it would have come up before by now. But I was unable to find a duplicate, hence the answer above. If anyone is aware of a duplicate I've overlooked, I welcome any suitable notice of that.)
Recently, I came across the InternalsVisibleTo way of making internal classes and methods visible to other assemblies. Though this is very useful in an application where you have a whole bunch of assemblies and you want to avoid circular dependency or code duplication, some of us think this could expose a security flaw. What are your thoughts?
For example, if I have an attribute thus:
[assembly: System.Runtime.CompilerServices.InternalsVisibleTo("foo")]
Even if this were hidden away in an assemblyInfo.cs file, one could discover this through disassembly, etc. And not everyone signs or obfuscates their assemblies. Now, armed with the information that there may be more functionality up for grabs, I can create my own assembly called foo.dll and then make use of methods/classes that I previously could not.
There's no security flaw here because the public/private distinction has nothing to do with security. Members are not "hidden" as private for security reasons, but rather for design reasons. Anyone could find all your private methods by reflection and call them directly anyway, even if InternalsVisibleTo is not set.
If you don't want "accidental" replacements (I say accidentally because member visibility is not a security measure) you need to use strong name signing of the target assembly you are wanting to make visible (your source assembly will also need to be strong named, see the remarks section of the MSDN for InternalsVisibleToAttribute).
so the following attribute
[assembly: InternalsVisibleTo("foo")]
will become
[assembly: InternalsVisibleTo("foo, PublicKey=002400000480000094" +
"0000000602000000240000525341310004000" +
"001000100bf8c25fcd44838d87e245ab35bf7" +
"3ba2615707feea295709559b3de903fb95a93" +
"3d2729967c3184a97d7b84c7547cd87e435b5" +
"6bdf8621bcb62b59c00c88bd83aa62c4fcdd4" +
"712da72eec2533dc00f8529c3a0bbb4103282" +
"f0d894d5f34e9f0103c473dce9f4b457a5dee" +
"fd8f920d8681ed6dfcb0a81e96bd9b176525a" +
"26e0b3"")]
Then only assemblies that where signed with the private key that corresponds with the public key listed in the attribute will be able to view your assembly's interals.
You should in the first place avoid using InternalsVisibleTo if you can. I rarely even use the internal accessibility on types, and even more rarely find a need for those types to be accessible to an assembly other than the one in which they are declared.
That said, the attribute does exist for a reason, and in some very rare cases it really is needed. In those cases, as you've found, if the referenced assembly is not signed, then anyone can build such an assembly and then the internals in your own assembly will be visible to it.
And no, there's not anything you can do about that. .NET has no way to recognize the "correct" assembly unless it's signed. That's precisely why signing exists.
So, if you really want to restrict access to the internal members of the assembly, then you need to use strong-naming (i.e. signing the assembly) so that .NET can tell the difference between the correct assembly and an imposter.
My experience is that InternalsVisibleTo is essential for sound unit testing.
I agree with previous answers that string name signing is key to minimizing security holes. If you want to be double-secure - I wrap a (#IF DEBUG) around the InternalsVisibleTo declaration. Then it's not compiled when you go to RELEASE.
I have an assembly with functionality that I don't want exposed as public but still accessible to my other assemblies. This can be done using InternalsVisibleToAttribute by specifying each assembly that it will make its internals visible to.
I was wondering if there is a way that I didn't have to specify all the referencing assemblies but instead just enforce the rule that an assembly must be signed by the same snk to have the internals made visible.
Does this functionality exist and if so, could someone point me in the right direction?
No, I don't believe anything like that is available automatically.
You could write your own tool to generate the [InternalsVisibleTo(...)] lines, and add unit tests to ensure that all such references have the same key though.
I'm not aware of anything that enforces this for you and automatically generates the InternalsVisibleTo but you could write a Visual Studio Extension that does that.
I hope that the utility I created few years ago can make your life a little bit easier to add InternalsVisibleTo to your AssemblyInfo.cs file.
Here's the link:
http://vkreynin.wordpress.com/2007/12/09/testing-internals-members-with-internalsvisibleto-attribute/
I have the idea that it might be useful to enforce type visibility between namespaces rather than assemblies (internal) in C#.
It would seem that such a concept would assist developers working with a codebase, ensuring the correct types are used in places where another internal type supplying similar functionality is available, but would result in "architectural" disadvantages (unwanted dependencies etc).
Do others think this would be useful and is it currently possible? If not why not?
Also, would the concept of preclusions - the ability to specify negative constraints on references between namespaces and / or assemblies be a useful addition to C#?
A type is strongly bound to the assembly in which it is defined. A namespace is not, it can appear in multiple assemblies. System.Configuration for example.
Let's assume for a moment that the metadata format for an assembly would be changed (-1 billion points) to store attributes for a namespace. Those attributes would still have to be stored in an assembly because that's the storage unit for metadata. Now you have to deal with the possibility that the CLR loads another assembly and finds the same namespace but with conflicting attributes. How could it possibly resolve that?
More seriously, how would you prevent external code from simply using the same namespace and attributes to suddenly get access to implementation details that were meant to be private. This completely destroys the value of having the internal keyword.
You could make them public, tag them with a custom attribute, and then add a FxCop rule to check for accesses from the outside of the namespace.
This doesn't securely enforce the restriction and fails when the member is accessed with reflection, but if it's only about policy/codingstyle this should be enough.
I think there is also an existing attribute to hide members from Intellisense which you might use in conjunction with your custom attribute.
I have got a dll placed in a shared folder over development server. Is there any way to use that dll without adding reference in my application and without installing the same in GAC.
Thanks in advance.
Assembly asm = Assembly.LoadFrom(path);
See MSDN for late binding, reflection etc.
Small edit: A variable with the keyword "as" is asking for trouble. So "Assembly as" changed to "Assembly asm" should be safer.
You may want to look at the Managed Extensibility Framework or at Assembly.Load... in the base framework.
Why would you want to do this, though? You'd need to call any code within the Assembly via reflection (hence the suggestion that the MEF may be what you're really after).
Yes, it is possible...somehow. Have a look at the Assembly-Class. With it you can load assemblies from a file without knowing what you exactly load.
Using Assembly.LoadFrom would be the only way to have zero references, but you'd still need to share contracts.
What's the problem with adding a reference?
What are you going to do when someone wants to work on a laptop and the WiFi goes down?
Yes,
you can call Assembly.Load() and then make use of Reflection to call into the public interface (lowercase "interface" - what I mean is the methods, fields and properties) exposed by the assembbly.
But in order to do that you need to know what methods to call. It helps if you can be certain that the assembly includes classes that do conform to a known .NET interface.
This idea is the basis for "plug-in" architectures in many tools, where the tool loads any assembly in its "plugin" directory, instantiates classes, casts the result to an ISomething, and then invokes methods via that interface.
I also would read Suzanne Cook's .NET CLR Notes.
http://blogs.msdn.com/suzcook/default.aspx
If this assembly is in a shared folder, you may find that .NET security restrictions stop you working with classes in that assembly in quite the way you'd expect.
Rather than storing on a shared folder, you may want to consider checking in the assembly to your source code repository. (I've seen a "/lib" folder used to good effect for this). Then you can reference the assembly directly.
(There are also repository solutions such as Maven that can more properly control this. However, they don't play well with .NET, unfortunately.)