C
HAPTER
24
| Authentication Commands
Secure Shell
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4. Set the Optional Parameters – Set other optional parameters, including
the authentication timeout, the number of retries, and the server key
size.
5. Enable SSH Service – Use the ip ssh server command to 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.
N
OTE
:
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.
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