Writing Binary To file in Visual Basic with the intent of unreadability

Question

I am working on a program that creates a "license" file. This file is expected to be binary, containing a name, today's date, a warning date, an expiration date, and a preference of Metric or Imperial units of measurement, and essentially authorizes programs to work until the expiration date is reached, before which the warning date notifies the user that the license will expire. For this functionality to be fully utilized, the dates must not be able to be easily edited so as to prevent people from setting the date to whatever they want and keeping the program.

What I have now writes each field from a String or Integer into whatever the BinaryWriter class deems should be written when I use its "write" method. I have been experimenting with the difference between Big and Little Endian encoding, which is selectable in the form.

[code redacted]

If the entered name has no spaces, the file looks a bit unreadable, but not enough. With Big Endian, most of the Expiration Date is still showing; with Little Endian, the other two dates are mostly visible. However, using spaces in the entered name changes the format of the outputted text quite a bit, making all characters deliminated by a space, and therefore incredibly easy to change. My apologies that I cannot actually show you what the files look like.

Is there a better/more accepted way of storing this data? I would like the license files to work with existing FORTRAN programs, of which read unformatted files in the general structure I've detailed, but reverse-engineering this sounds a bit difficult from what I've read and my employer has offered to rewrite the FORTRAN files to accept this new license creation program if need be.

Nicholas Carey · Accepted Answer · 2011-05-25 20:52:34Z

1

Create your license structure as text, containing whatever data you need (XML is a convenient format).

Encrypt that using public key encryption (using your private key).

Embed the public key in your app. Decrypt the license file with the public key. Deal with it as you need to.

Easy!

answered May 25, 2011 at 20:52

Nicholas Carey

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gpcz · Accepted Answer · 2011-05-25 20:50:41Z

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Most license managers I've seen tend to show the license information in plain text, followed by a checksum code that the program checks against, most likely the data hashed with some other random stuff. That provides the benefit of having a human-readable license file while being hard to change.

Be advised that license managers like these will make casual copying difficult, but someone determined to run your program without a license will still be able to crack it with a disassembler and some time.

answered May 25, 2011 at 20:50

gpcz

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JAB · Accepted Answer · 2011-05-25 20:52:16Z

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The most secure way to do that would probably be to encrypt the license file and have the programs using the licenses decrypt the file and display the info in it as necessary.

answered May 25, 2011 at 20:52

JAB

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