Conditions for running the program

Question

I wrote a main program in C#, and I worte also a small tool program also in C#.

I want that the tool program will be able to execute under some conditions:

• When called from my main program.
• When called from open some suffix of file (e.g. "*.abc")

But if the user open my program directory he can run the tool program, and I do not want him to be able to do it. I want him to be able to run the program under the conditions above. And if he ran the program manually, the program automatically shut.

Is there any way to do that?

Answer 1

To check if your main program called it, you could pass the main program's ProcessID as a commandline argument, then in your small program, check if that ProcessID exists and if its process name is the name of your main program. This isn't spoof-proof, but might be a bit trickier to fake than just passing a static number/string.

In addition, you could encrypt the number and pass that, then decrypt it and check the above. It's pretty much impossible to prevent a determined hacker from running your program on its own, but you can raise the bar of how tricky it is to do it. You'd also want to obfuscate your code, otherwise a quick Reflector call will show exactly what characters are being passed.

Alternatively, if possible, you could just make the small program a DLL and call it from your main program like that. This would need a bit of refactoring, but would force your program to be open. As for opening a *.abc file, your program can check the command line arguments to see if a filename was passed through. This can then be processed automatically by your app and the DLL calls can be made.

Answer 2

There is nothing exposed to the process/executing environment that tells it how it was invoked, so there is no foolproof way to do this.

You can have your main program pass in a flag on the command line - this and the suffix are things that you can check for and if either one does not exist you terminate immediately.

However, if the user ever guesses the flag, they can still call the application directly.

Other mechanisms could involve writing a value to a file from your main program just before invoking the second program and checking that file from your second program (and deleting it after execution), as a messaging mechanism. There are other messaging mechanisms that would do similar things (private MSMQ queues for instance).