I'm looking for a network file system that works on all three of Linux, Mac OS X, and Windows, and has secure authentication. Secure data transfer is a smaller priority, but that would be nice too. I'd also like it to be invisible unless you know exactly where to look.

Put another way: how can I enable all three of these OS's to access files off of my Ubuntu Linux fileserver without exposing to everyone on the network that a file share exists, while assuring that no one on the network can access the share without proper authorization even if they do find it?

None of the computers in question have static IP addresses, and I expect to be able to refer to them by some unchanging name. I have working Bonjour/Avahi name resolution for anything that bothers to go through the DNS name resolver library.

Also, it should, for the most part, *just work*. Kerberised NFSv4 would be disqualified even if OS X and Windows supported it; I'm not going down that rabbit hole again. I'm toying with the idea of SSH tunnels and either NFS or SMB/CIFS, but both seem to present immediate difficulties.

Again, I'm not terribly worries about someone sniffing packets, so long as the share doesn't advertise itself, and has a secure logon.

Am I asking too much? It *shouldn't* be too much, but yeah.