Chapter 10 Ssh Protocol; Introduction - Red Hat LINUX 7.2 Reference Manual

Section 10.1:Introduction
10 SSH Protocol
This chapter covers the benefits of the SSH™ protocol, the sequence of events that occur when a
secure connection is made to a remote system, the different layers of SSH, and methods to ensure
SSH is used by users connecting to your system.
Common methods for remotely logging into another system through a shell (telnet, rlogin, or
rsh) or copying files between hosts (ftp or rcp) do not encrypt data that is sent over the connection
between the client and the server, and should be avoided. Instead, you should only connect to a remote
host using a secure shell or an encrypted virtual private network. Using secure methods to remotely
log in to other systems will decrease the security risks for both your system and the remote system.

10.1 Introduction

SSH (or Secure SHell) is a protocol for creating a secure connection between two systems. In the SSH
protocol, the client machine initiates a connection with a server machine. The following safeguards
are provided by SSH:
• After an initial connection, the client can verify that it is connecting to the same server during
subsequent sessions.
• The client can transmit its authentication information to the server, such as a username and pass-
word, in an encrypted format.
• All data sent and received during the connection is transferred using strong encryption, making it
extremely difficult to decrypt and read.
• The client has the ability to use X11
provides a secure, graphical interface (called X11 forwarding).
The server benefits from SSH, as well, especially if it is running a number of services. If you use port
forwarding, otherwise insecure protocols (for example, POP) can be encrypted for secure communi-
cation with remote machines. SSH makes it relatively simple to encrypt different types of communi-
cation normally sent insecurely over public networks.
Red Hat Linux 7.2 includes the OpenSSH server (openssh-server) and client (openssh-
clients) packages, as well as the general OpenSSH package (openssh) which must be installed
for either of them to work. Please see the Official Red Hat Linux Customization Guide for instructions
on installing and deploying OpenSSH on your Red Hat Linux system.
1 X11 refers to the X11R6 windowing display system, traditionally referred to as X. Red Hat Linux includes
XFree86, a widely used, open source X Window System, which is based on X11R6.
1
applications launched from the shell prompt. This technique
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