[CentOS] Remote backup of server

Hello,

I want mount directory of one server to another over internet. I was
looking to NFS4, but there are no security mechanisms. I need
encrypted connection using private key (something like SFTP).

Or - if there is in CentOS repo (or EPEL) package, that can mount
directory over internet using private key and make differential backup
(like rdiff-backup).

Thank you very much for links or other resources work up
Martin Šťastný