For logging on to a Linux server, a key can also be used instead of the password. The key is simply generated on the client and imported on the server. The server then trusts the client and does not require a password for access.

Execute the following on the client:

ssh-keygen -t rsa

copy the key to the server:

ssh-copy-id -i ~/.ssh/id_rsa.pub root@Server

see: http://wiki.ubuntuusers.de/SSH#Authentifizierung-ueber-Public-Keys