Hi!

I have this program created and I have always been thinking about serial keys. How they work and stuff.

How about this idea - if one would employ a subscription-style payment system for his application in which customers would pay on a half-year or something like that basis in order to renew their subscription (antivirus and so on), how safe would this be:

1. supply a file (txt or whatever else), which contains a very (can be argued about - enough to cause confusion in a user with little IT experience) long sequence of numbers
2. the customer, after the payment order has been completed, receives this file and imports it into the system (this can be automatic or whatever, usability's not the issue here at the moment)
3. [within the system] the system takes certain digits out of the file, which make up the date until which the renewed subscription is valid and notes it somewhere internally.
4. now, until the expiry date, the system is working correctly.

Please, be honest and constructive critisism only!

Thanks!