Securely backing up Linux machines to NAS?

[srehrlich-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org (Scott Ehrlich)]

I have been tasked with having a Buffalo Terastation Pro 2 NAS box,
likely to be connected to a Linux box via samba, be the storage device
to back up mostly Ubuntu and Centos systems. ?The trick is, the
machines to be backed up need to do so in an automated fashion and
make a secure, encrypted connection to my Linux box hosting the NAS.
The NAS does have SSL enabled for web admin access, though the same
login credentials are used to authenticate the Linux host via samba to
the NAS.

So what are the simplest options to back up the Linux hosts? ? rsync
does come to mind, but how to do so securely from each host? ? I'd
consider something via ssh, but that would mean an interactive login,
and encrypting individual files on the hosts is not an option.

NFS is also available on the NAS, but considering the security
concerns, I will not use that, nor do I want to enable any more
services on the linux machines being backed up than necessary, meaning
samba is not an option, unless it remains the ONLY one.

I ONLY plan to use samba to mount the NAS to my Linux server, unless
someone comes up with a more secure method, or even away to negate the
need of the Linux server and permit the hosts to back up directly to
the NAS...

Ideas are welcome.

Thanks.

Scott