Chapter 12
| Security Measures
Configuring the Secure Shell
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4. Set the Optional Parameters – On the SSH Settings page, configure the optional
parameters, including the authentication timeout, the number of retries, and
the server key size.
5. Enable SSH Service – On the SSH Settings page, enable the SSH server on the
switch.
6. Authentication – One of the following authentication methods is employed:
Password Authentication (for SSH v1.5 or V2 Clients)
a. The client sends its password to the server.
b. The switch compares the client's password to those stored in memory.
c. If a match is found, the connection is allowed.
Note:
To use SSH with only password authentication, the host public key must still
be given to the client, either during initial connection or manually entered into the
known host file. However, you do not need to configure the client’s keys.
Public Key Authentication – When an SSH client attempts to contact the switch,
the SSH server uses the host key pair to negotiate a session key and encryption
method. Only clients that have a private key corresponding to the public keys
stored on the switch can access it. The following exchanges take place during
this process:
Authenticating SSH v1.5 Clients
a. The client sends its RSA public key to the switch.
b. The switch compares the client's public key to those stored in memory.
c. If a match is found, the switch uses its secret key to generate a random
256-bit string as a challenge, encrypts this string with the user’s public
key, and sends it to the client.
d. The client uses its private key to decrypt the challenge string, computes
the MD5 checksum, and sends the checksum back to the switch.
e. The switch compares the checksum sent from the client against that
computed for the original string it sent. If the two checksums match,
this means that the client's private key corresponds to an authorized
public key, and the client is authenticated.
Authenticating SSH v2 Clients
a. The client first queries the switch to determine if DSA public key
authentication using a preferred algorithm is acceptable.
b. If the specified algorithm is supported by the switch, it notifies the
client to proceed with the authentication process. Otherwise, it rejects
the request.
c. The client sends a signature generated using the private key to the
switch.
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