There are different ways to achieve this
1) encrypted license files that contains the expiry dates etc.
2) encrypted license keys held in the registry
3) challenge/response mechanism which require an internet connection
4) probably others.......
Try:
License Key Generation[
^] or:
How can I create a Product Key for my C# App[
^] or:
c# Licensing[
^]
Couple of them are in C# which can be seen to start on Vb.NET
Also,
Cryptography 101 for the .NET Framework[
^]
Hope this helps.
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