HP A5830 Series, Руководство по настройке

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5.
The server compares the version number carried in the packet with that of its own. If the server
supports the version, the negotiation succeeds, and the server and the client proceed with key and
algorithm negotiation. Otherwise, the negotiation fails, and the server breaks the TCP connection.
All packets involved in the preceding steps are transferred in plain text.
Key and algorithm negotiation
The server and the client send algorithm negotiation packets to each other, notifying the peer of the
supported public key algorithms, encryption algorithms, MAC algorithms, and compression algorithms.
Based on the received algorithm negotiation packets, the server and the client figure out the algorithms
to be used. If the negotiation of any type of algorithm fails, the algorithm negotiation fails, and the
server tears down the connection with the client.
The server and the client use the DH key exchange algorithm and parameters such as the host key pair
to generate the session key and session ID, and the client authenticates the identity of the server.
Through the process, the server and the client get the same session key and session ID. The session key
is used later to encrypt and decrypt data exchanged between the server and client. The session ID is
used to identify the session established between the server and client and is used in the authentication
stage.
Before the key and algorithm negotiation, the server must have already generated a DSA or RSA key
pair, which is used in generating the session key and session ID and by the client to authenticate the
identity of the server. For more information about DSA and RSA key pairs, see "
Configuring public key ."
Authentication
SSH supports the following authentication methods:
•
Password authentication —The SSH server uses AAA for authentication of the client. During
password authentication, the SSH client encrypts its username and password, encapsulates them
into a password authentication request, and sends the request to the server. After receiving the
request, the SSH server decrypts the username and password, checks the validity of the username
and password locally or by a remote AAA server, and then informs the client of the authentication
result. If the remote AAA server requires the user for a password re-authentication, it carries a
prompt in the authentication response sent to the client. The prompt is transparently transmitted to
the client and displayed on the client to notify the user to enter a specified password. After the user
enters the correct password and passes validity check on the remote AAA server, the server returns
an authentication success message to the client.
•
Publickey authentication —The server authenticates the client by the digital signature. During
publickey authentication, the client sends the server a publickey authentication request that contains
its username, public key, and publickey algorithm information. The server checks whether the public
key is valid. If the public key is invalid, the authentication fails. Otherwise, the server authenticates
the client by the digital signature. Finally, the server sends a message to the client to inform it of the
authentication result. The switch supports using the publickey algorithms RSA and DSA for digital
signature.
An SSH2.0 server might require the client to pass both password authentication and publickey
authentication or either of them. However, if the client is running SSH1, the client only needs to pass
either authentication, regardless of the requirement of the server.
The steps of the authentication stage are as follows:
1.
The client sends the server an authentication request that includes the username, authentication
method, and information related to the authentication method (for example, the password in the
case of password authentication).