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we can develop trial version easily that when user install product then end date will store in registry. when apps will run then every time we check the system date is less that or equal to end date. if yes then apps will run otherwise apps will give a message for purchasing product. this way we can develop trial version but there is one problem that user can change the system date and run the software and also user can delete the registry entry. in big companies what measures are taken to develop trial product which will run on single machine if internet connection is not there.

if anyone knows the industry standard logic then please share with me.

Mou
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2 Answers2

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This step is often delegated to 3rd party tools, such as NET Reactor or Dotfuscator.

Those tools (and others) will not only obfuscate your code, but can also support various degrees of licensing protection.

For instance, NET Reactor will let you specify timeouts, or number-of-times-run to expire your application. You can then distribute license files to unlock the app for another period of time (or permanently).

Dotfuscator has some fancy features where your app can report back to your server when it is run, when exceptions occur, etc. allowing you to get an idea of how your app is behaving in the wild, in addition to supporting various licensing models.

Of course, your customers may or may not like the idea of the app 'phoning home', but the tools are out there if that's what you want.

jwd
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  • Someone had edited my answer to include [CryptoLicensing](http://www.ssware.com/cryptolicensing/cryptolicensing_net.htm) - I'll just include it here in the comment rather than changing the original answer. – jwd Aug 02 '12 at 19:39
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If you don't want to spend money on a third-party tool (which is probably your best option), I would suggest some sort of encrypted value in the registry that stores the end date. Make the key necessary for the system to run. When they register the software, just make the end date well off into the future (say the year 3000 or something). That way they cannot delete the key and they can't just modify it by hand without messing it up.

In the end, you can get more and more tricky but someone is going to find a way around your protection. Either send out limited installs (with only a few features) or figure out how much effort you want to put into protection compared to the reward for doing so.

IAmTimCorey
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  • I'll add to xor the date with the host-name or a stuff like that before encrypting. The effect is the key is working only on the good computer. – ykatchou Jul 31 '12 at 06:41