Validate a DLL

[paulb]

I am looking for methods you could use to validate that a particular DLL an app is using is the real thing, i.e. it hasn't been replaced by something else with the same function signatures in it. I was thinking of using a query-response type system when the application first starts up, something like: 1. call a function 'Hello()' on the DLL passing in a callback function as argument to it 2. DLL responds by calling the function supplied within a certain time frame, e.g. after 1 second but before 3 seconds. 3. If callback function is called within the time period then it validates and the app continues to use DLL I know this isn't perfect, any other methods that may be more robust? thanks,