3Com 8807 Configuration Manual page 770

770 C 67: SSH T
HAPTER ERMINAL
S
ERVICE
W orkstation W orkstation
Local Ethernet Local Ethernet
Laptop Laptop
PC
Server Server
SSH client SSH
Figure 181 Establish an SSH channel through a WAN
To establish an SSH authentication secure connection, the server and the client
must go through the following five phases:
1 Version number negotiation:
The client sends a TCP connection request.
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After the TCP connection is established, the server and the client negotiate the
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version number.
If the negotiation succeeds, the key algorithm negotiation phase starts;
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otherwise, the server tears down the TCP connection.
2 Key algorithm negotiation:
The server generates an RSA key pair randomly, and sends the public key in the
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key pair to the client.
The client uses the public key from the server and a random number generated
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locally (in length of eight bytes) as parameters to calculate the session key.
Using the public key from the server, the client encrypts the random number
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for calculating the session key and sends the result to the server.
Using the local private key, the server decrypts the data sent by the client and
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obtains the random number used by the client.
The server uses the public key and the random number from the client as
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parameters to calculate the session key with the same algorithm as on the
client. The resulting key is 16 bytes long.
On completion of the above steps, the server and the client obtains the same
session key. During the session, both ends use the same session key to perform
encryption and decryption, thereby guaranteeing the security of data transfer.
3 Authentication mode negotiation:
The client sends its username information to the server.
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Local switch
WAN WAN
Remote switch
SSH SSH server
W orkstation
Remote Ethernet Remote Ethernet
Laptop Laptop
PC PC
Server Server