rsync is a very nice tool to synchronize two directories, especially if they are on different machines. If you require confidentiality of the transferred data, rsync works great over ssh.
Besides the standard password authentication, ssh also supports public key authentication. This key-based authentication has the added bonus of having per-key options:
- you can restrict the source IP from which this key may be used
- you can force a command to be executed instead of allowing the connecting side to specify one
