The Secure Shell (SSH) protocol is a method for secure remote login and other secure network services over a public network such as the Internet. SSH services a number of applications across multiple platforms including UNIX, Windows, Mac, and Linux.

You can use SSH:

• For login to a shell on a remote host, replacing the need for telnet and rlogin (see FIGURE 11-3 for an example of an application that uses SSH for this application)
• For executing a single command on a remote host, replacing the need for rsh
• For file transfers to a remote host
• In combination with rsync to back up, copy, and mirror files securely
• In conjunction with the OpenSSH server and client to create a full VPN connection

The SSH protocol consists of three major components:

• TLS provides server authentication, confidentiality, and integrity with perfect forward secrecy (use of an independent session key for every web session a user starts in order to protect data)
• User Authentication Protocol (UAP), which authenticates the client to the server
• Connection Protocol, which multiplexes the encrypted tunnel into several logical channels

For more information on SSH, see http://tools.ietf.org/html/rfc4251.