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Approach to obfuscate an embedded dll in a WPF application

I have a WPF application whose output is a.exe. This application is dependent on an external b.dll (whose source code I have access to).
Requirements:
The output should only be a.exe which should contain the dll. I don't want to provide my users with a separate dll (if it can be avoided)
I should be able to obfuscate the code. (I don't want anyone to be able to modify it).
Approaches tried:
I embedded b.dll inside a.exe, it worked. But I was not able to obfuscate the exe as it gave an error that it was unable to find b.dll.
I obfuscated a.exe and b.dll but it did not work. It was unable to find b.dll.
Alternate approach :
Is there any way that I can perhaps add the spruce code of b.dll to my project and have the dll be compiled to the exe itself rather than a separate dll.
Is it possible to make this alternate approach work or are there any other ways ?
If nothing works, I know that I can compile a and b separately, obfuscate a and provide b as a separate file (what I'm trying to avoid).
Apologies for the formatting issues, if any, I'm using the android app. Let me know if you need any details.

I have had great success with Eazfuscator.Net in the past.
http://www.gapotchenko.com/eazfuscator.net
To run it from the command line enter the following command:
Eazfuscator.Net.exe -n a.exe b.dll
It will combine the two files into a single exe. The main program will be able to access the dll.
You can even set up Visual Studio so that the command line above runs as a post compile event.

Assembly embedding may seem quite confusing, so here is how it's usually done:
The dependencies are obfuscated if needed.
The target assembly is obfuscated. At this point, the obfuscator is also instructed to embed certain dependencies as a part of obfuscation process.
As a result, the embedded assemblies are stored as a resource of the target assembly.
In order to load dependencies at runtime, obfuscators usually install a handler for AppDomain.AssemblyResolve event that is raised by CLR when it fails to resolve an assembly automatically.
The handler extracts and loads an embedded assembly from the resource.
That's it. A good obfuscation tool allows achieving that quite easily. I don't see why it wouldn't work in the case with WPF application. If there are problems, I would recommend contacting product support.
Another option is assembly merging. Unlike embedded, the merged assemblies become an inseparable part of the target assembly code. For this reason, the assembly merging often helps to achieve a better obfuscation coverage and application startup time comparing to embedding. Although it may look a better option, merging may sometimes break the application functionality.

Referencing a 3rd party assembly which is not located in the root location

I have a Visual Studio 2010 C# project which creates an .exe and this project is using some 3rd party class library.
My project is located in: /MyFramWork/tests/test1
3rd party library is located at: /MyFrameWork/bin/utils/
I am adding the reference to the library by using References->Add Reference->Browse. I can see that in the project file all is fine:
....\bin\utils\log4net.dll
False
I would like to reference the 3rd party library without using the option "Copy Local". However if I don't use the option, the library is not found and I get an exception.
My question is: Is there a way to specify that the 3rd party library should be found at ....\bin\utils. It seems that when the .exe gets build the information from the .csproj gets lost.

By default, .NET apps look for their dependencies in only two places: the EXE directory, and the GAC (Global Assembly Cache).
You have three choices:
You can make sure the dependency gets copied into the same directory as your EXE (this is what Copy Local does). This is the best choice most of the time, which is why it's the default when you reference an assembly that's not already in the GAC.
You can install your dependency into the GAC using gacutil. This might be a good choice if your dependency isn't going to change, is going to be in a different location on every development machine (i.e. if relative paths won't work well), and if you want to use it from many different projects. But it's a major pain if the dependency is still under active development and changing frequently. You'll also need to make sure to put the DLL into the GAC on every computer you deploy your app to.
You can customize the dependency-loading behavior so it looks in other places, as Hans noted in his comment. This is an advanced option and comes with a whole new set of headaches.
Normally, you would just use Copy Local; it's a very sensible default. You should need a fairly compelling reason to do anything different.

Use the <probing> element to specify where the CLR should search for your assemblies. The only restriction is that the assemblies must be located in subdirectories of your application's base directory.
For example, if your application base directory is C:\MyFramework, then you could have your assemblies in C:\MyFramework\bin.
Have a look at this article to learn how the CLR searches for assemblies.

If you need to load assemblies from custom locations, you could try the Assembly.LoadFile Method.
The following links may be useful:
C# - Correct Way to Load Assembly, Find Class and Call Run() Method
http://www.csharp-examples.net/reflection-examples/

It's me Potzon. I am still investigating this incredibly silly problem.
I have been hoping for some elegant solution. I am about to build fairly large framework with lots of assemblies which would be placed inside /Framework/bin/. However I wanted to have some directory structure inside the the directory, for example /bin/utils, /bin/test, /bin/devices/ and so on.
One possible solution that I have found is to define environmental variable DEVPATH (see here http://msdn.microsoft.com/en-us/library/cskzh7h6.aspx) but it turns out that .net4 is not using this variable when an assembly is run independently (outside the visual studio), or at least this is the case for me - I can't make it work.
It seems that the solution to put all the assemblies inside the /bin directory without using sub-directories is the best. I think I will give up and just do it this way.

How can C# use a legacy DLL simply without registration(regsvr32)

Situation
I run a build system that executes many builds for many project. To avoid one build impacting another we lock down the build user to only its workspace. Builds run as a non privileged users who only have write ability to the workspace.
Challenge
During our new build we need to use a legacy 3rdparty DLL that exposes its interface through COM. The dev team wants to register the build(regsrv32.exe) but our build security regime blocks this activity. If we relax the regime then the 3rdparty DLL will impact other builds and if I have two build which need two different versions I may have the wrong build compile against the wrong version (a very real possibility).
Question
Are there any other options besides registration to handle legacy DLLs which expose their interface via COM?
Thanks for the help
Peter

For my original answer to a similar question see: TFS Build server and COM references - does this work?
A good way to compile .NET code that references COM components without the COM components being registered on the build server is to use the COMFileReference reference item in your project/build files instead of COMReference. A COMFileReference item looks like this:
<ItemGroup>
<COMFileReference Include="MyComLibrary.dll">
<EmbedInteropTypes>True</EmbedInteropTypes>
</COMFileReference>
</ItemGroup>
Since Visual Studio provides no designer support for COMFileReference, you must edit the project/build file by hand.
During a build, MSBuild extracts the type library information from the COM DLL and creates an interop assembly that can be either standalone or embedded in the calling .NET assembly.
Each COMFileReference item can also have a WrapperTool attribute but the default seemed to work for me just fine. The EmbedInteropTypes attribute is not documented as being applicable to COMFileReference, but it seems to work as intended.
See https://learn.microsoft.com/en-ca/visualstudio/msbuild/common-msbuild-project-items#comfilereference for a little more detail. This MSBuild item has been available since .NET 3.5.
It's a shame that no-one seems to know anything about this technique, which to me seems simpler than the alternatives. It's actually not surprising since I could only find just the one above reference to it on-line. I myself discovered this technique by digging into MSBuild's Microsoft.Common.targets file.

There's a walkthrough on registration-free COM here:
http://msdn.microsoft.com/en-us/library/ms973913.aspx
And excruciating detail here:
http://msdn.microsoft.com/en-us/library/aa376414
(the root of that document is actually here: http://msdn.microsoft.com/en-us/library/dd408052 )
Also, for building in general, you should be able to use Tlbimp or tlbexp to create a TLB file that you can use for building, assuming the point of registering is just to be able to compile successfully, and not to run specific tests.

Installation tools such as Installshield can extract the COM interfaces from the DLLs and add them to the registry. It can also use the self-registration process of the DLL (which I believe is what regsvr does), but this is not a Microsoft installer best practice.

in .NET COM is normally done thru Interop in order to register .DLL in .NET they are called Assemblies and that can be done several ways.. by adding references via VS IDE at the project level, or writing code that Loads and unloads the assembly.. by .Config file that haas the reference to the assembly as well as the using of that reference within the project... GAC.
If you have access to the 3rd party .DLL's you can GAC them, and reference them in your project
you can add a using to your .cs file header as well as add the reference to the project by right clicking on reference --> add Reference ...
you can also do the above step as well as set the copy local = true in the properties for that .dll.. I hope that this gives you some ideas.. keep in mind that .NET assemblies are Managed code so there are several ways to Consume those 3rd party .DLL's using other methods within C# like LoadFromAssembly ect..

Thanks for all the help.
We changed from early-binding to late-binding because we never really needed the DLL at compile time. This pushed the registration requirement from the build server to the integration test server (where we execute the installer which handles the registration). We try to keep the build system pristine and have easy-to-reset integration systems.
Thanks again
Peter

How can I integrate an external assembly as a resource into a .net executable

I have an application that makes use of/consumes services from a number of external .net libraries, which in turn calls certain executables. Would it be possible to integrate these into one huge executable and load them from my application to the disk as required? Resources come to mind but not sure how that is done.
Thanks,

You have several options to do that:
use ILMerge (free)
For howto see here and here
OR
use some tool like SmartAssembly (commercial)
it can embed and merge among other things (no need to change your source code)
OR
code that yourself in less than 10 lines (free but minimal source code change)
mark all needed dependencies as "embedded resource" - this way they are included in the EXE file... you need to setup an AssemblyResolve handler which at runtime reads from Resources and returns the needed DLLs to the .NET runtime...

You can use ILMerge to merge all your assemblies into a single executable file.

You can find a complete example at CodeProject.

Linking statically in C#

I'm working on a module for a CMS. This module is distributed as a class library DLL.
I have several utility libraries I'd like to use in this module. Is there anyway I can link these libraries statically so I won't have to distribute several DLL's (thereby distributing my utility libraries separately)?
I would like to have only one DLL.

You can merge your many DLLs with ILMERGE:
http://research.microsoft.com/~mbarnett/ILMerge.aspx
Haven't tried it myself. Hope it helps.
Download here:
http://www.microsoft.com/downloads/details.aspx?familyid=22914587-B4AD-4EAE-87CF-B14AE6A939B0&displaylang=en
Brief Description (from download-page)
ILMerge is a utility for merging multiple .NET assemblies into a single .NET assembly. It works on executables and DLLs alike and comes with several options for controlling the processing and format of the output. See the accompanying documentation for details.

If you don't want to use ILMerge, see this page:
http://blogs.msdn.com/b/microsoft_press/archive/2010/02/03/jeffrey-richter-excerpt-2-from-clr-via-c-third-edition.aspx
editor's note: Jeffrey Richter advices to put your dlls into exe file as resources (For each DLL file you add, display its properties and change its “Build Action” to “Embedded Resource.”). Then a custom class loader is needed to make the executable work (At runtime, the CLR won’t be able to find the dependent DLL assemblies, which is a problem. To fix this, when your application initializes, register a callback method with the AppDomain’s ResolveAssembly event).
Be sure to change the resourceName string to point to your actual resources. (e.g. change AssemblyLoadingAndReflection to your project name.)

The short answer for this is no!
You can not link in a dll during compilation.
I don't know if there is some subtle way to do this, but you would probably have to distribute the dlls along with your cms.
The best way to do this is to make some kind of re-distributable.