Suggest good authentication scheme for remote clients to connect via SSH?

view story

http://serverfault.com – I have a project where I'll have a number of remote Linux systems in the field. From time to time they'll need to connect to a central server via SSH. These remote systems are automated and have no user present. The number and IP of the remote systems is likely to change often, so keeping a central list of them may be difficult. I am looking at client certificates but they would require an addition to the know_hosts file on the server for each client? Given this what would be a good way for the single server to authenticate SSH connections from the remote machines? TY, Fred (HowTos)