NX Technology - Use of SSH Protocol and How SSH Tunneling Works in NX

Use of SSH Protocol and How SSH Tunneling Works in NX

NX uses the SSH protocol to send its data. SSH was chosen as a base for NX because of its excellent security record. NX relies on both the SSH functionalities and the existing open source SSH software, to make it possible to run contemporary Unix and Windows desktops and arbitrary network applications, across the Internet, in a secured and controlled way.

The way NX works (NX 3.x) is by creating an 'nx' user on the server machine whose shell is executed any time a remote NX user connects to SSH using NX Client. The initial login between client and server happens using a DSA key-pair. The public key-part is provided during the installation of the server: the private key-part is distributed together with NX Client. The SSH server is forced by the NX key to execute the nxserver shell and enables SSH X11 forwarding. Due to performance deterioration of SSHD, X11 forwarding was introduced in NX 2.0.0.

The SSH secure channel is established once the client has been authenticated on the server. Authentication of the user on the system and negotiation of session parameters happen on this channel. By default, NX Client is configured with encryption of all traffic enabled, i.e. NX tunnels all the session traffic over the encrypted SSH channel used to authenticate and negotiate the session with the server.

Starting from version 4.0, NX will also allow system login as an alternative method, so that users can choose if they want to rely on NX or SSH authentication..

In addition to simply allowing users to log in remotely over a slow internet link to a server graphically, NX also allows them to suspend and resume sessions. During suspension, the processes invoked inside the session continue to run, and so many people have come to use NX as a graphical alternative to SSH and the 'screen' application - in order to run applications such as XChat permanently on a computer with a fixed internet link. Another program that serves this purpose is xpra.