SSH is a simple idea but it has many parts, some of them complex. This chapter is designed to get you started with SSH quickly. We cover the basics of SSH's most immediately useful features:
Logging into a remote computer over a secure connection
Transferring files between computers over a secure connection
We also introduce authentication with cryptographic keys, a more secure alternative to ordinary passwords. Advanced uses of client programs, such as multiple keys, client configuration files, and TCP port forwarding, are covered in later chapters. Our examples in this chapter work with OpenSSH and Tectia on Linux and other Unix-inspired operating systems.
Suppose you're out of town on a business trip and want to access your files, which sit on a Unix machine belonging to your ISP, shell.isp.com. A friend at a nearby university agrees to let you log into her Linux account on the machine local.university.edu, and then remotely log into yours. For the remote login you could use the telnet program, but as we've seen, this connection between the machines is insecure. (No doubt some subversive college student would grab your password and turn your account into a renegade web server for pirated software and death metal MP3s.) Fortunately, both your friend's machine and your ISP's have an SSH product installed.
In the example running through the chapter, we represent the shell
prompt of the local machine, local.university.edu,
as a dollar sign ($) and the prompt
on shell.isp.com as shell.isp.com>.