>See if http://www.sweetpotatosoftware.com/spsblog/2005/08/30/VisualFoxProRandomLicenseSerialGenerator.aspx helps

Thanks, but not really. It shows how to get hash codes - I was planning to use a construction of my own, and those are probably better. But the real problem is how to get, not any activation code, but one that is time-restricted.

>
>>One of my clients wants something like a time-based activation code. I told him that this is not very secure, because any fool can change the computer's clock... but he still wants it.
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>>Now, the problem is, I don't know how to do it. I was thinking about the following limited solution: Get an activation code as a one-way has from the current month plus some salt (e.g., checksum of ("201203" + "Harry Potter rocks!")), tell the client that this is the activation code, and have him type it in (or type it in remotely, with GotoMyPC or similar).
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>>The program then re-does the calculation each time it starts, and checks whether it still gets the same activation code. If not, time to get a new activation code. This would work fine - except for the tiny little detail that the user might change the computer clock.
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>>My problem now is, I wanted something more flexible - a solution that allowed a shorter or a longer time period - ideally, a period of any desired length. Any ideas?
>>
>>TIA,
>>
>>Hilmar.