ZyXEL Communications USG-100@USG-200 - V2.20 ED 2 - How SSH Works

Chapter 50 System
ZyWALL USG 100/200 Series User’s Guide
862
SSH is a secure communication protocol that combines authentication and data
encryption to provide secure encrypted communication between two hosts over an
unsecured network. In the following figure, computer A on the Internet uses SSH
to securely connect to the WAN port of the ZyWALL for a management session.
Figure 568 SSH Communication Over the WAN Example
50.8.1 How SSH Works
The following figure is an example of how a secure connection is established
between two remote hosts using SSH v1.
Figure 569 How SSH v1 Works Example
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.