SSH authentication with pre-shared key

Create new key on client
#ssh-keygen -t rsa
#(confirm with 3x with enter to leave passphrase empty)
ssh-keygen -q -f ~/.ssh/id_rsa -N ''

Copy public key to server
ssh-copy-id ${USER}@192.168.0.1

Test login
ssh -v ${USER}@192.168.0.1

Login with private key
ssh -i ./backup_ssh_key/id_rsa USER@YOUR_SERVER

Import own ssh key by using previous / master ssh key
cat ~/.ssh/id_rsa.pub | ssh -i ./backup_ssh_key/id_rsa USER@YOUR_SERVER 'cat >> .ssh/authorized_keys'

OPTIONAL: Disable password login on server
http://www.panticz.de/SSH-server-enable-disable-password-authentication

LINKS
http://linuxproblem.org/art_9.html
http://www.pro-linux.de/work/rootserver/teil2.html
http://www.schlittermann.de/doc/ssh
http://ubuntuforums.org/showthread.php?t=625926
http://www.la-samhna.de/library/brutessh.html
http://linux.justinhartman.com/Secure_SSH_server_with_Public/Private_key_authentication
http://mikiwiki.org/wiki/ssh_%28Shell-Befehl%29