Storing files encrypted and sharing them over NFS or other

I have a tricky question for you, well at least seems tricky to me.

Here is the setup. I have a linux file server and another linux server. I am looking to use the disk space from the filer server on the other linux server. The only catch is that I would like the data to be encrypted on the filer server to avoid have random people looking into the data.

So to sum up, the data needs to be encrypted on the file server but mountable on the other linux server via NFS or some other protocol.

The solution needs to be at least free and/or open source.

Thank you in advance for your help !

I think encfs is a good starting point. Since I'm also interested in this, I'll try and set one up and let you know how it goes.