This system demonstrates one way to encrypt license keys at your office, which can then be provided to customers, whose software then decrypts the codes.

"Master Software File" is assumed to be the main file of your customer's solution that he has downloaded or bought from you. This file decrypts whatever license key the customer inputs, and determines his privileges, expiration date, etc.

"Administration" is the file you use to generate license keys for your customers. This system only encrypts an expiration date and the customer's customer number. You could add any other characters to the string to add support for additional privileges.

Brian Dunning
http://www.briandunning.com/