INTRODUCING SSH
The SSH protocol allows one computer running an SSH client to securely connect
to another running an SSH server. In other words, SSH is a client-server protocol.
The computer initiating the connection is referred to as the client, and the computer
being connected to as the server.
SSH operates over TCP, and while SSH servers can listen on any TCP port, by
default SSH servers listen on port 22. As its name suggests, security is integral to
the Secure Shell, and all SSH traffic is encrypted by default.
SSH is often described as the secure replacement for the older insecure Telnet
protocol. It’s certainly true that SSH provides a secure replacement for Telnet, but
it’s much more than that, providing additional features Telnet never did.
The first version of SSH dates back to 1995, which sounds old in IT terms, but
bear in mind that Telnet dates back to 1968! The first version of the SSH protocol
had some security shortcomings, so a new version of the protocol, SSH 2, was
released in 2006, and this is what we use today.
Some Preliminaries
To play along with this segment you’ll need two computers with SSH installed the
SSH service enabled on at least one of those computers, and TCP/IP network
connectivity between them.
