From: Florian Gross <flgr@...>
Date: 2005-02-05T12:00:20+09:00
Subject: Re: Ruby for closed source projects

Michael Gebhart wrote:

> well, open source is pretty nice. But in some cases I don't want to show
> the sourcecode to other users. Maybe because of an encryption, or an
> special algorithm. Is there any chance to hide the code? Compiling the
> application with the interpreter directly? 

Not that I want to sound academical or religious or anything, but if 
your encryption algorithms need to operate in the dark to be secure they 
probably aren't working very well. Also note that copying source code is 
not legal so you might not even need to obfuscate it to get protection 
against naive copy attempts.

That aside it's quite hard to hide code well -- just have a look at Java 
where there's disassemblers that can produce pretty readable code from 
byte code and there's lots of people reconstructing algorithms directly 
from machine code -- if the machine can read it, it is quite likely that 
an human will also be able to do so -- it's just a matter of how hard it 
will be for him to do so. You're really only safe if you have the code 
logic residing on an external server which will just take input and give 
back output without disclosing how it processed the information.

There's tools available that will make reconstructing of the source code 
non-trivial for inexperienced users -- RubyScript2Exe[1] and Exerb[2] 
come to mind. But note that these just encode the unfiltered source code 
directly and if somebody knows how that is done he can reconstruct the 
original source code.

Other approaches include taking the code itself and making it harder to 
read for humans (via variable/method/class name substitution or removing 
meaningless whitespace) and dumping Ruby's syntax tree directly. The 
latter is quite similar to how Java does this and can for example be 
accomplished via NodeWrap[3]. I think I also heard about somebody 
modifying Ruby itself (you are allowed to do so even without releasing 
the source code of your modified Ruby) so that it would use a different 
mechanism for loading code.

I hope you can understand the trouble associated with all this and will 
still find a solution that works for you.

[1] 
http://www.google.com/url?sa=U&start=1&q=http://www.erikveen.dds.nl/rubyscript2exe/&e=9818
[2] http://exerb.sourceforge.jp/index.en.html
[3] http://rubyforge.org/projects/nodewrap/