Question

I am doing an Online Quiz project in C#. The test client is a Windows Desktop Application running on Windows XP. I need to block the control+alt+delete key combination to prevent students from minimizing/closing the application.

Using PInvoke is okay for me.

I know this is definitely possible because I have seen three applications doing this. They are all proprietary, so I have no way of knowing how it was done.

Answer 1

For Windows XP, the correct way to do this is to create your own Graphical Identification and Authentication Dynamic Link Library, or gina.dll for short. Here’s an MSDN article about it. This DLL exports a set of functions that interact with the Winlogon process and provides the user interface to logon requests – the Secure Action Sequence event. The main logon request is the ctrl-alt-delete response. The standard gina.dll invokes the logon screen or the task manager/logoff dialog. It’s not too difficult to create your own gina but it does require C/C++ coding and not C# and it is quite easy to make the system fail to boot. This does not stop people from pressing F8 at boot up and selecting the Safe Boot option, which won’t load the custom gina.dll.

EDIT: I should also say that you don’t need to implement all the functions the gina is required to implement, you can dynamically load the previous gina.dll and pass all the calls you’re not interested in to the old gina.dll.

EDIT 2: This does not work with Vista/Win7 as they changed the architecture of the logon process. It is still possible to disable ctrl-alt-delete in Vista/Win7 but it requires a different mechanism – there are MSDN articles about it somewhere.

EDIT 3: Here’s a ZIP file containing the source code to make a gina.dll It was built using DevStudio 2005. The file GinaInterface.cpp details the steps needed to install the new gina.dll library. This will disable the “Welcome” screen and replace it with the ‘press crtl-alt-del’ to login dialog. As it stands, there is no difference between this and a standard gina.dll, all the gina related calls are passed through to the original gina.dll file (called msgina.dll in the Windows\System32 folder). To disable the ctrl-alt-del key press, update the function WlxLoggedOnSAS in GinaInterface.cpp. To stop ctrl-alt-del whilst your application is running, you could create a named mutex (CreateMutex) and test for its presence in the gina.dll, stopping ctrl-alt-del if the mutex exists.