Windows form applicaion with expiration date

Question

Hello

I've developed C# application in which needs to have an expire date.
It's a simple windows form application which users can run exe file for a limited time only. Maybe later I might need to go with installer for my application. Anyhow, The application should stop working after 90 days for instance or maybe on any specified date (20th of June 2014 ) for example.

What is the right way to get time stamp for my application? I think I need to write C# function which compare Dates and times. I've read that xml file can be used or maybe to write to registries. I have no idea from where to start. Can you provide me with some practical solution? or maybe the write code to achieve this?

Vulpes · Answer

If you want to write the expiry date to the registry then you'll need code such as this: using System; using System.IO; using Microsoft.Win32; // needed for registry access static class Program { static void Main(string[] args) { int period = 30; // trial period string keyName = Software\Rano\SomeApp; long ticks = DateTime.Today.Ticks; RegistryKey rootKey = Registry.CurrentUser; RegistryKey regKey = rootKey.OpenSubKey(keyName); if (regKey == null) // first time app has been used { regKey = rootKey.CreateSubKey(keyName); long expiry = DateTime.Today.AddDays(period).Ticks; regKey.SetValue(expiry expiry RegistryValueKind.QWord); regKey.Close(); } else { long expiry = (long)regKey.GetValue(expiry); regKey.Close(); long today = DateTime.Today.Ticks; if (today > expiry) { Console.WriteLine(Your free trial has expired. Please register to continue using the application); return; } } // code for rest of application Console.WriteLine(Rest of application continuing ...); Console.ReadKey(); } } Rather than writing the actual date I've converted it to 'ticks' and then stored that. If you're worried that your users may be knowledgeable enough to change the registry key with Regedit then you can set the keyName and the name of the value (expiry' in the SetValue method) to anything you like which will make them more difficult to identify.

Vulpes · Answer

Check out this previous thread for some ideas on this: http://www.c-sharpcorner.com/Forums/Thread/226656/limited-trial-period-in-c.aspx

theLizard · Answer

Everything Vulpes says is fine BUT there is more to limiting the use of software after a set period of time. Writing to the registry is ok I do it myself BUT first you need to be sure what you are doing with it because doing the wrong thing can destroy the registry. The problem with doing what Vulpes says is this int period = 30; // trial period string keyName = Software\Rano\SomeApp; long ticks = DateTime.Today.Ticks; If you identify your software this way all that a person needs to do is delete the registry key and start fresh with another 90 days. Apart from this c# is not that secure anyone using tools available on the internet can reverse engineer you application and get ALL the source code you have written. If you want to go the path of using the registry you should consider using a key generated using a GUID like {E5B80D24-60E3-44A3-B0A9-58F7F8994EAA} so you end up with Software\ {E5B80D24-60E3-44A3-B0A9-58F7F8994EAA}\SomeApp SomeApp would be a value you would obtain by using something like MD5 encryption which could be 2A967C97E9F822B26294F3FE1EBEF283 So you would then have Software\ {E5B80D24-60E3-44A3-B0A9-58F7F8994EAA}\2A967C97E9F822B26294F3FE1EBEF283 as your registry key as you can see there would be no way a casual user would ever identify your application from this. There are many other things you would need to consider as well things like having a license file linked to the computer hardware so that your application only runs on the computer that it was installed on using a license key. Protecting software is not a simple task.

Echo Zhu · Answer

I tried this code also but when comes to long expiry = (long)regKey.GetValue(expiry);  it shows error msg :'Object reference not set to an instance of an object.' Anyone knows how to fix it? Thanks alot~

Rano AH · Answer

Thanks Vulpes.  Got it!

Rano AH · Answer

Hi Vulpes Creating the text file and store the date and time is not really good practice in my case. I might need to use the settings.properties or make it hard coded with registries. Can you please guide me through registries or any other way to make the timestamp hard coded? Thank you.