Need to generate unique serial numbers using algorithm

[Alseikhan]

I sell an Excel worksheet and need to protect it with a unique serial
number that is provided separately to each customer upon purchase
(i.e., each customer gets a unique number).
How can a procedure be implemented in VBA to validate serial numbers
and to block randomly generated numbers by non-subscribers?
For customer convenience, the number should be around 6 characters
long.

Ideally, that procedure will validate the serial number without having
to index it against a huge database of valid numbers stored somewhere
in the sheet.
Web connectivity, to tap into a central server for number validation,
cannot be assumed.
In a nutshell, what is needed is something akin to serial numbers used
to protect commercial software.

Any help is appreciated.
alseikhan

 

[chillihawk]

This is an interesting problem. Have you considered a combination of
digits limited in their range, something like:

Digit 1: can only be 1 or 0
Digit 2: can only be 3 - 7
Digit 3: can only be 4 - 8

and so on. Then use the VBScript Regular Expressions library or write
your own parser to confirm the rules have been met.

 

[RB Smissaert]

It shouldn't be too difficult to make a number that can be validated without
a
database, but where will the code be that validates the number?
As mentioned many times in this NG the security of Excel is not very good.
Maybe this needs to be tackled first.

RBS