Licensing a database app

We are developing a database application that tracks vehicles. We need a method to limit the number of vehicles the application will track.

The application is licensed on a per vehicle basis. If a customer wants to track 1000 vehicles, then the customer must buy a 1000 vehicles license and the application must then enforce that limit.

The application uses an ODBC data source (SQL Server or Oracle) and VB COM components to access the data. The database is installed on the customer's server. *** Therefore the customer has full control over the database content and database structure. *** Any solution must take into account the customer can change any field of any table and modify the structure of the database in any way.

Currently, we are thinking of storing this limit in a table in the database and encrypting the contents of each field using the Microsoft CryptoAPI. The VB components can then perodically decrypt the relavant fields (using a hardcoded key) and enforce the limit.

How have others solved this problem? Any suggestions?

Thanks,
Brian Received on Mon Jun 22 1998 - 00:00:00 CEST