호스트에서 재생성
sudo ssh-keygen -f /etc/ssh/ssh_host_rsa_key -N '' -t rsa
sudo ssh-keygen -f /etc/ssh/ssh_host_dsa_key -N '' -t dsa
sudo ssh-keygen -f /etc/ssh/ssh_host_ecdsa_key -N '' -t ecdsa -b 521
클라이언트에서 삭제
ssh-keygen -f ~/.ssh/known_hosts -R my_ssh_server.com
