Chapter 21. OpenSSH
OpenSSH is a free, open source implementation of the SSH
(Secure SHell) protocols. It replaces telnet, ftp, rlogin, rsh, and rcp with secure, encrypted network connectivity
tools. OpenSSH supports versions 1.3, 1.5, and 2 of the SSH
protocol. Since OpenSSH version 2.9, the default protocol is
version 2, which uses RSA keys as the default.
If you use OpenSSH tools, you are enhancing the security of your
machine. All communications using OpenSSH tools, including
passwords, are encrypted. Telnet and
ftp use plain text passwords and send all
information unencrypted. The information can be intercepted, the
passwords can be retrieved, and your system could be compromised by
an unauthorized person logging in to your system using one of the
intercepted passwords. The OpenSSH set of utilities should be used
whenever possible to avoid these security problems.
Another reason to use OpenSSH is that it automatically forwards
the DISPLAY variable to the
client machine. In other words, if you are running the X Window
System on your local machine, and you log in to a remote machine
using the ssh command, when you run a
program on the remote machine that requires X, it will be displayed
on your local machine. This feature is convenient if you prefer
graphical system administration tools but do not always have
physical access to your server.
