Crypto library needed

One of my friends has a client who needs someone to write a strong file encryption tool for him (that someone being me). Now, there's a bunch of approaches I can think of for this, so here goes:

1) Write a VB or C frontend for a program such as GNUPG (this is probably the simplest approach, but I don't want to do this).

2) Get a good strong crypto library and use it in a C/C++ program to encrypt files.(I'm leaning towards this approach). I tried libgcrypt but it only builds on *NIX and not on Windows, so that was a dead end.

3) Toughest, longest method. Get the algorithm for something like blowfish and write everything from scratch (could be fun, but I don't think I have that much time).

So, what I would really appreciate is to get pointed towards a good, secure cryptographic library that is free (as in GPL or BSD free or free for commercial use) that works in Windows. It would be an added bonus if there were binaries available.
Also, this is what I was thinking of suggesting to this guy. Use my program to generate a secret and a public key. Give it a username, password, comment, blablabla. Keep the public key on the machine and allow anyone to encrypt using it. Keep the private key in a secure location, such as a CD-R which is either carried on his person always or kept in a secure location and load it off the Read Only media (ie never copy it to his hdd). Anything wrong with this (sorry if these are dumb questions, but I'm a crypto n00b).
Thanks in advance.
Cheers,
cgkanchi

http://www.eskimo.com/~weidai/cryptlib.html - Crypto++ 5.1 -> I've never used this, but is appears to have huge support for many different algorithms, both Public and Private Key. Their SourceForge website ( https://sourceforge.net/project/show...?group_id=6152 ) also has download links, but the first one seems to describe parts better, and has other mirrors. I think that their license allows you to use it, but it isn't GPL. It is public domainish, but you should look at it for yourself. http://www.eskimo.com/~weidai/License.txt

Good luck. Hope that helps and that you can compile it.

I think GNUPG comes with a bunch of files that contain algorithm code. Being that it is Open Source you might check out the exact terms of the licence and see if you can use those...

Tim_axe, I'd already found Crypto++ and it *seems* to be pretty good. Thanks anyway. Oh, and I had no problems compiling it. Anyone had any experience with it? Hypronix, thanks, I did not know that (I should've guessed, it being GPL'ed and all). I might have to do that if crypto++ doesn't work out.
Cheers,
cgkanchi