I normally use NFS, however I am not so comfortable with the security as basically a root user can just change his UID to an arbitrarily one in order to obtain access to a shared folder.

Moreover, access can be restricted based on the IP address of a machine, but someone who has access to the router can temporarily change his IP address (to one having access).

I think the best solution would be a shared file system which uses public key authentication to manages access rights, e.g. similar to ssh.

Does such a technology exist for a **multi-user** network file system in linux with **concurrent read/write** access?