Iam new to VB.Net windows applications
please can anybody help for the following problem.

I want to validate application based on a time period.The admin will initialise the Initial time key, current time key and period for which the application needs to be functioned,these are encrypted and updated in the registry.

Application should stop functioning in the following cases

1.Current time key is ahead of system date.
2.the difference between current time key and initial time key is more than specified period.

Thnx in Advance