Comments by Ammar Asjad Raja (Top 1 by date)

1. Saved Dates for license should be in encrypted form in database table.
2. License Period information should be get from database table and should be decrypted to calculate difference of days
3.A user can change system date but cant change database server dates and if a user will change database server date then user cant decrypt already encrypted dates values stored in database table.
hope it helps or let me know for description and explanation with code.