I have a program designed in VB.net for a wafer probing system. The software has 3 main components that come standard and three that are options. When a customer decides not to have the three options they are disabled but still in the program. If at some point they decide to buy the options, one of our technicians would have to go there and be able to access the program with an administrative account to enabled the components.
Does anyone have any suggestions on what the easiest way to accomplish this?
The absolute simplest mechanism would be to create a registry key for each component, set them to 0 by default, and have the technician change them to 1. The program would just check the registry key every time a user tries to access one of the optional parts of the application.
You could get fancier and give each customer a license key for each component, and the license keys would be stored instead of 0 or 1. If the license key validates (based on some secret property that every generated license key shares) then you let them access the optional part of the application. This has the advantage that you can keep records of who is given which key, so if your software starts getting copied around the internet, you know who shared their license key. Also it would be more difficult (not much more difficult) to unlock the optional components without paying.
The trouble is, in both cases you’re at the mercy of security through obscurity and it would be rather simple to unlock the full program without paying. You have to rely on penalty clauses in your contract to scare them away from changing those values or sharing their license keys. If your customers’ machines ever connect to the internet you could try submitting the values of the registry keys to a web service periodically to ensure compliance (this is evil).
Unfortunately, that’s kind of the end of the story. There has really never been a successful technology-based DRM scheme that has survived scrutiny over time, even on platforms where they designed the hardware. Basically what I’m saying is, this is an unsolved problem, so don’t overthink it.