LAN P2P File sharing - Not Server Based

Hi,

Just wanted to see what people think on this...

I am at Uni, and what to get file sharing going in halls, for such things as ehh Linux and freeware software....

However I don't want a server running 24/7 for example line Direct Connect.

Is there a piece of software that people can use that is only available to the LAN users.

Security would also be good, some kind of encryption key. I remember seeing a piece of software that did have a key and you connect to everyone with a key, though can't remember..

Any help would be greatly appreciated.

Thanks