Its generally not worth the hassle to do this- because of the fact that "fair use" (and for that matter every other "exception" to the exclusive rights to copyright) is a statutory right, not just a mere "exception" in the case law to copyright. That essentially means that it is possible to 100% legally use a key generator to crack your program if the purpose is to copy the software for the purpose of carrying out one of the statutorily enumerated exceptions to copyright rights. Therefore, DRM in the area of software is more problems than what its worth. Also, you'd need to make sure you're abding by the .NET licenses which will be inherited to the product. Currently, Microsoft does not allow encryption of the .NET framework components, so you would likely be out of license doing something like this.