Digisol DG-FS4528P, Management Manual

Page: 179 / 973

C
HAPTER
7 | Security Measures
Configuring the Secure Shell
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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.
c. The client sends a signature generated using the private key to
the switch.
d. When the server receives this message, it checks whether the
supplied key is acceptable for authentication, and if so, it then
checks whether the signature is correct. If both checks succeed,
the client is authenticated.
N
OTE
:
The SSH server supports up to four client sessions. The maximum
number of client sessions includes both current Telnet sessions and SSH
sessions.