I wish to implement my software on a shareware basis, so that the user is given a maximum trial period of (say) 30 days with which to try out the software. On purchase I intend the user to be given a randomly-generated key, which when entered enables the software again.
I've never been down this route before, so any advice or feedback or pointers to 'standard' ways of how this is done would be much appreciated.
I do not anticipate users cheating by changing the system date or anything like that, though this is probably worth considering. Apologies if this topic has appeared before.
With regards to a random-generated key, how will you verify a key is legit or if a key is bogus if it is actually random? Have a look at the article "Implementing a Partial Serial Number Verification System" as it is quite good and is easy to implement in any language.
With regards to time trials, as basic solution would be to compare your main executable files creation time to the current system time and act on the difference. This assumes your installer sets the files creation time to the time of install as opposed to preserving the time you compiled it! :)
Also watch out for the time changing radically, if the current date is magically less than the install date and such.
One way to get around this type of datelock is to change your date before you install to be years in the future. So you should check that the date today is not less that the install date.
If your software is really useful, you'll certainly find cracked copies on P2P before you see your first order. This will happen no matter how sophisticated is the license enforcement code you are going to implement.
That said, just store first-run date somewhere (may be registry, if on Windows) and after 30 days refuse to start, or just open a reminder window.
Don't worry about cheaters, they'll find a way around your restrictions no matter what. Worry about your honest customers and try hard not to make their life harder.
Eric Sink has written more about this here (section 4).
On the first start, you can store the actual date somewhere.
Each following start, you look for the stored date, if it exist you read it an if it is more than 30 days after the first start, you stop the program.
Please see this library.
Description:
Convert any application into time-limited shareware. Generate serial numbers to register it. A function library offering a flexible locking system with solid encryption. Easy to implement. Support for VB, C++, Delphi, other languages.
来源：https://stackoverflow.com/questions/173930/incorporating-shareware-restrictions-in-c-software