ssh keys

http://rcsg-gsir.imsb-dsgi.nrc-cnrc.gc.ca/documents/internet/node31.html

the target (ie the server you want to login to with out a password) needs the public key from the source host/user in the ~/.ssh/authorized_hosts file (or authorized_keys, depending on your os)

generate the public/private keys with ssh-keygen -t rsa

not really that hard, is it?