ZyXEL Communications 200 Series - Manual (Page 690)

Chapter 43 System
ZyWALL USG 100/200 Series User’s Guide
690
Figure 514 SSH Communication Over the WAN Example
43.7.1 How SSH Works
The following figure is an example of how a secure connection is established between two
remote hosts using SSH v1.
Figure 515 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.
2 Encryption Method
Once the identification is verified, both the client and server must agree on the type of
encryption method to use.
3 Authentication and Data Transmission
After the identification is verified and data encryption activated, a secure tunnel is
established between the client and the server. The client then sends its authentication
information (user name and password) to the server to log in to the server.