Licensing an EXCEL file

  • Thread starter Thread starter Grace
  • Start date Start date
G

Grace

My boss wants to market an analysis file I have. He wants to license it to
users on a per year basis. What will be ciritical is that no one can see
the eqautions and that, somehow, it will expire in a year.

Is password protection good enough that no one, short of a really
accomplished hacker can break it? Also, can someone tell me how to best
install an expiration date, one that can't be beaten easily?

Thanks,
Grace
 
password protection is useless. See

http://www.mcgimpsey.com/excel/removepwords.html


If you're not putting your functions in a compiled add-in, your formulas
will be visible to anyone with enough smarts to find these newsgroups.
Of course, going the COM add-in route eliminates sales to XL97/Mac
users, but that may be acceptable.

Expiration dates are as vulnerable as the code - generally a hidden file
is used to store date information so that the user can't just set the
machine's clock back. The date can be encrypted within a block of random
data to make it less obvious which data contains the date. Of course,
knowing that, it's not too hard to find hidden files and hack them, but
most business users won't be able to/interested in doing that. To be
commercially acceptable, you'll probably need to include some code
within your add-in for updating the license via a new license code.
 
Yes, that code breaker does work nicely. Ouch!

Can you direct me to soemwhere I can learn about this COM add-in route. It
sounds promising.

Also, kindly lead me to somehwere i can learn about using an add-in for my
licensing?

Thanks much!

Grace
 
For COM, take a look here and at the included links:

http://support.microsoft.com/default.aspx?scid=kb;en-us;291392


For licensing, I can't tell you very much. I've designed my own systems,
but most of my software is completely open source to the client. Other
systems I've worked on have been under Non-disclosure agreements.

In general, you'd want to have a routine in your code that's capable of
authenticating a license code which contains as part of it a new
expiration date. The code would then have to update the hidden file(s).
 
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