The Secure Shell (SSH) protocol uses encryption to provide authentication and privacy when logging in to other computers over a network, such as Romulus, Remus, or the Computing Cluster. It can also be used to securely execute remote commands. By default logins use a password, but it's also possible to set up passwordless connections. The latter are very convenient, and are also required to initiate remote commands. However, for security reasons they should not be used from computers that are accessible to others.