What is SSH and how does it work?
Secure Shell (SSH) is a program to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another. It provides strong authentication and secure communications over insecure channels. SSH provides secure X connections and secure forwarding of arbitrary TCP connections.
SSH works by the exchange and verification of information, using public and private keys, to identify hosts and users. The ssh-keygen command creates a directory ~/.ssh and files that contain your authentication information. The public key is stored in ~/.ssh/id_rsa.pub and the private key is stored in ~/.ssh/id_rsa. Share only your public key. Never share your private key. To further protect your private key you should enter a passphrase to encrypt the key when it is stored in the file system. This will prevent people from using it even if they gain access to your files.
One other important file is ~/.ssh/authorized_keys. Append your public keys to the authorized_keys file and keep the same copy of it on each system where you will make ssh connections.
In addition, on Owens the default SSH client config enables hashing of a user’s known_hosts file. So if SSH is used on Owens the remote system’s SSH key is added to ~/.ssh/known_hosts in a hashed format which can’t be unhashed. If the remote server’s SSH key changes, special steps must be taken to remove the SSH key entry:
ssh-keygen -R <hostname>