Intended Audience
We've written this tutorial for system administrators and technically minded users. Some chapters are suitable for a wide audience, while others are thoroughly technical and intended for computer and networking professionals.
End-User Audience
Do you have two or more computer accounts on different machines? SSH lets you connect one to another with a high degree of security. You can copy files between accounts, remotely log into one account from the other, or execute remote commands, all with the confidence that nobody can intercept your username, password, or data in transit.Do you connect from a personal computer to an Internet service provider (ISP)? In particular, do you connect to a Unix shell account at your ISP? If so, SSH can make this connection significantly more secure. An increasing number of ISPs are running SSH servers for their users. In case your ISP doesn't, we'll show you how to run a server yourself.Do you develop software? Are you creating distributed applications that must communicate over a network securely? Then don't reinvent the wheel: use SSH to encrypt the connections. It's a solid technology that may reduce your development time.Even if you have only a single computer account, as long as it's connected to a network, SSH can still be useful. For example, if you've ever wanted to let other people use your account, such as family members or employees, but didn't want to give them unlimited use, SSH can provide a carefully controlled, limited access channel into your account.
Prerequisites
We assume you are familiar with computers and networking as found in any modern business office or home system with an Internet connection. Ideally, you are familiar with the Telnet and FTP applications. If you are a Unix user, you should be familiar with the programs rsh, rlogin, and rcp, and with the basics of writing shell scripts.
System-Administrator Audience
If you're a Unix system administrator, you probably know that the Berkeley r-commands (rsh, rcp, rlogin, rexec, etc.) are inherently insecure. SSH provides secure, drop-in replacements, eliminates rhosts and hosts.equiv files, and can authenticate users by cryptographic key. SSH also can increase the security of other TCP/IP-based applications on your system by transparently "tunneling" them through SSH encrypted connections. You will love SSH.
Prerequisites
In addition to the end-user prerequisites in the previous section, you should be familiar with Unix accounts and groups, networking concepts such as TCP/IP and packets, and basic encryption techniques.