ASP.NET What's the best way to produce a trial version for customers to download?

I've written a ASP.NET app that I hope to sell to businesses, I could host the trial but it's designed to connect to the customers data so customers will certainly want to install it to do a successful evaluation.

I've never produced anything commercial before so I'm looking for advice on how best to limit the trial, a 30 day trial seems most common, do you simply rely on the clock of the PC/Server they install it on? Any other suggestions welcome, please keep in mind this is ASP.NET app so will be installed on thei开发者_如何学运维r web server.

Thanks Craig

I would just do it via the PC's clock. At the end of the day, they could just change the clock and continue to use your software, though it's probably not going to work in practice (i.e. most software actually uses the date/time for other things as well and changing it going to screw that up).

Generally, you can usually trust business more than you trust the general public. The liability of a business is much higher than that of an individual, so if it came to it, you could potentially sue them for quite a bit. That alone means most businesses will purchase licenses for all of their software: a few hundred (or even thousand) dollars for a software license is much better than risk getting sued.

When they sign up for the demo, make sure you get all of their contact details and so on.

I would setup a web service on your server to authenticate the demo application. The web service should get called periodically and if it fails, then shut down the application. That way you have complete control over the trial (you can extend it or shut it down remotely).

You should give them some sort of key which they will place in your web.config that will identify them as a customer.

Make sure you take the usual precautions of encrypting / using hashes with both the key and the web service so it's not bypassed.

This sort of thing has been well covered on SO in the past.

You cannot make it unbreakable, but you can make it very difficult for the client to break your trial period.

One way to do it is to take the first run time and encrypt that info and store it either in your web.config or database. This has a weakness though: what do you do if the value is not present where you expect it to be?

Another option is to ping a webservice that you host. If the webservice says their trial is over then you can render the appropriate page to tell them that. This has the advantage that the webservice is beyond their control and cannot be messed with. It has the disadvantage that not every client will want to be allowing their web app to phone home, and there may be connectivity issues which would interfere with the functioning of your app.

So you might want to come up with a variety of options, and then implement a licencing module using the Provider pattern, so that you can swap in the licencing module most suitable for that client.

Put a counter in the web.config, of course give the counter a non-related name so the customer does not know what it is for. Every time they access the application you can increment the counter. Give them x number of log-in's.

If you want you can encrypt the counter if you do not want the customer to figure out that the counter is incrementing.