How Ssh Works - ZyXEL Communications USG40 User Manual

Figure 604 SSH Communication Over the WAN Example

43.8.1 How SSH Works

The following figure is an example of how a secure connection is established between two remote
hosts using SSH v1.
Figure 605 How SSH v1 Works Example
Host Identification
1
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.
Encryption Method
2
Once the identification is verified, both the client and server must agree on the type of encryption
method to use.
Authentication and Data Transmission
3
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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