Trial software and registering

[Dar Scott]

On Mar 18, 2005, at 11:07 AM, Alex Tweedly wrote:

>> I
>> check the creation date of the latest file as my check file for the
>> current date and compare that against the timeout date.
>>
> Why is that not "vulnerable  to turning back the system clock" ?
> If I set my system clock to a year ago, then each time I access the 
> web, I'll create my cookie files with dates in 2004.

Perhaps, that would not be vulnerable to _temporarily_ turning back the 
system clock.  It might be reasonable to check for dates lots of places 
and then assume that the current real date is the latest of those or 
later.  One can't prove that a demo is valid, but it the assumption 
holds then one can prove that it has expired.

Dar

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