Connecting via SSH, requires a user provide his identity to the remote machine using one of several methods. One method lets you access the remote system without entering a password at each login. Normally, when you log in to a system, you authenticate by entering your password for that system. Your password goes, as it is typed, to the remote system, which authenticates it against the /etc/passwd or /etc/shadow file. By contrast, SSH allow a “password-less” authentication method based on public-key cryptography.