ZyXEL Communications ZyXEL ZyWALL 5 - Manual (Page 342)

ZyWALL 5 User’s Guide
Chapter 21 Remote Management 341
Figure 173 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.
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.
21.7 SSH Implementation on the ZyWALL
Your ZyWALL supports SSH version 1.5 using RSA authentication and three encryption
methods (DES, 3DES and Blowfish). The SSH server is implemented on the ZyWALL for
remote SMT management and file transfer on port 22. Only one SSH connection is allowed at
a time.