Re: 30 days trial immune to set clock back in time?

Lew <>
Fri, 19 Sep 2008 08:11:02 -0400
Tomer wrote:

Can anyone guide me how can i create a 30 days trial to a software
that is immune to having set the clock back in time?

Can you assume an internet connection on the target machine? Or demand one?

Hit an NTP server for the time.

How much harm will it do if you rely on a clock that people can reset? How
many potential customers will be willing to reset their BIOS clock daily for
the sake of just your program? Is your program that good and/or that
expensive that people would cheat their entire system clock just to avoid a
license fee?

Have a feature in your program depend on correct time. Accounting software
won't be very useful if the date never advances beyond some 30-day boundary.

Keep an internal encrypted store of the datetimes "seen" by the software each
time it starts. If an earlier datetime is "seen" after a later one, refuse
access. I wouldn't even wait for the 30-day limit in such a case. Once the
31st day is "seen", assuming a forward-only clock that whole time, shut down
until payment.


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