4 ssh overview, 5 how ssh works, 4 ssh overview 32.5 how ssh works – ZyXEL Communications GS-2750 User Manual

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Chapter 32 Access Control

GS-2750 User’s Guide

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32.4 SSH Overview

Unlike Telnet or FTP, which transmit data in clear text, SSH (Secure Shell) is a secure
communication protocol that combines authentication and data encryption to provide secure
encrypted communication between two hosts over an unsecured network.

Figure 156 SSH Communication Example

32.5 How SSH works

The following table summarizes how a secure connection is established between two remote
hosts.

Figure 157 How SSH Works

1 Host Identification

The SSH client sends a connection request to the SSH server. The server identifies itself
with a host key. The client encrypts a randomly generated session key with the host key
and server key and sends the result back to the server.
The client automatically saves any new server public keys. In subsequent connections,
the server public key is checked against the saved version on the client computer.