Debian
ssh-keygen ssh-copy-id -i ~/.ssh/id_rsa.pub username@servername
OSX
ssh-keygen ssh-add ~/.ssh/id_rsa cat ~/.ssh/id_rsa.pub | ssh servername -l username 'mkdir .ssh ; cat >>.ssh/authorized_keys'
backup RSA key over rsync
rsync -avz --delete --sparse ~/.ssh/id_rsa.pub /target/target