How Ssh Works; Figure 17-11 Ssh Communication Example; Figure 17-12How Ssh Works - ZyXEL Communications ZYWALL2 ET 2WE User Manual

ZyWALL 2 Series User's Guide

17.6 How SSH works

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

Figure 17-12How SSH Works

17-14

Figure 17-11 SSH Communication 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.
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