[ale] win32-linux compatible encrpytion of files

[Jay Loden]

Ok, this is somewhat complicated to explain:

My *only* Windows project (legacy from before moving to Linux) is a virus 
removal tool that I keep updated often (daily/weekly).  It is the only thing 
that keeps me from ditching Windows entirely, since I still need to update 
the definitions every so often, which at the moment requires using Visual 
Studio to recompile.

I want to move the defs into an external file, but I want to make sure the 
external file isn't able to be just edited by anybody and therefore use my 
tool to harm computers or screw up the removal.  What I want to do is be able 
to update the definition file on a Linux box, encrypt it on Linux, then have 
the Win32 application read in the encrypted file and decrypt it to use for 
definitions.  This way, I stay on Linux and I can still make updates safely.  
So basically, I need any solution you guys can suggest that lets me 
effectively trade an encrypted file back and forth between Linux and Windows 
(hopefully with a "key" or "pin" needed to decrypt it).  Obviously, it has to 
be a library or something similar that I can call from  a C++ program.  

I also would need a good way to package this so that Windows users of, shall 
we say, "less than great" computer knowledge can download and run the file. 
(A windows installer would also require Windows, which defeats the purpose). 
A zip file works for *most* people but I've run into a pretty amazing number 
of people that don't have zip support even in this day and age. 

Thanks so much for any replies!
-Jay