SSH, The Secure Shell: The Definitive Guide, 2nd Edition

Chapter 1. Introduction to SSH

Many people today have multiple computer accounts. If you’re a reasonably savvy user, you might have a personal account with an Internet service provider (ISP), a work account on your employer’s local network, and a few computers at home. You might also have permission to use other accounts owned by family members or friends.

If you have multiple accounts, it’s natural to want to make connections between them. For instance, you might want to copy files between computers over a network, log into one account remotely from another, or transmit commands to a remote computer for execution. Various programs exist for these purposes, such as ftp for file transfers, telnet for remote logins, and rsh for remote execution of commands.

Unfortunately, many of these network-related programs have a fundamental problem: they lack security. If you transmit a sensitive file via the Internet, an intruder can potentially intercept and read the data. Even worse, if you log onto another computer remotely using a program such as telnet, your username and password can be intercepted as they travel over the network. Yikes!

How can these serious problems be prevented? You can use an encryption program to scramble your data into a secret code nobody else can read. You can install a firewall, a device that shields portions of a computer network from intruders, and keep all your communications behind it. Or you can use a wide range of other solutions, alone or combined, with varying ...