How do I create a time-limited application that can be unlocked with a serial number?

[FooBear]

I'm building a PocketPC application that I'd like to be able to
secure with a serial number or encrypted license code. Ideally, I
want to offer an full-function, 30-day time-limited evaluation of the
app that can be unlocked when the user buys a license.

Has anyone seen any code examples of this sort of thing? There's a
commercial offering, 1WAY, that I've seen, but it doesn't work on the
PocketPC platform.

I really hate having to reinvent the wheel and am hoping that I've
just missed something really obvious -- a set of convenient objects in
the Compact Framework, maybe???

-- Tony

 

[Guest]

One possibility using either the registry or hidden files...

When you app runs, try to open and read a registry key (or use a file
instead) containing the installation date. If the key or file does not
exist (during 1st run), create it and store the present date. The
subsequent times the app runs, the key will be present and you can just
check if the new current date is <30 days from the "install" date. Note
this is not 100% secure as one could theoretically delete/change the key or
hidden file. You can also store a "last time run" date check to prevent a
user from turning back the clock.
As far as a unlock code, you first have to check whether the device will
have a unique identifier. If not, you can make one up and store it. Then
you can make an unlock code specific to that ID and store it on the device
as well. Next time you run the app, if the unlock code is present, ignore
the 30 day expiration date. This method would make it unique to each
device.
There are various levels of complexity one can get into to prevent theft
etc., but you have to weigh it against the potential of annoying your good
customers.
HTH.
Dan

 

[Bryan Donaldson]

One thing you must remember : you're giving your application into the hands
of the enemy. There will be folks that get it and spend countless hours
attempting to crack your system, no matter what you choose. Some of them
will publish the results when they're successful, thereby reducing sales.
You need to weigh how much effort to put into securing your application
(cost) against how many sales you might protect (benefit).