VNC

http://en.wikipedia.org/wiki/Vnc

VNC

Virtual Network Computing

VNC - Overview

Virtual Network Computing (VNC) A graphical desktop sharing system

Uses the RFB protocol to remotely control another computer.

Uses a network Transmits the keyboard and mouse events from one

computer to another Relays the graphical screen updates back

VNC - Overview

Platform-independent VNC viewer resides any operating system

Can connect to a VNC server of any other operating system Clients and servers available for almost all GUI operating

systems and for Java Multiple clients may connect to a VNC server at the same

time Popular uses for this technology include

Remote technical support Accessing files on one's work computer from one's home

computer

VNC - Overview

Originally developed at AT&T The original VNC source code and many modern

derivatives are open source under the GNU General Public License

History

History

Created at the Olivetti & Oracle Research Lab Originally owned by Olivetti and Oracle Corporation In 1999 AT&T acquired the lab

2002 closed down the lab's research efforts Following the closure of ORL in 2002

several members of the development team formed RealVNC Continue working on open source and commercial VNC software

under that name Several other versions of VNC have been developed from the

original GPLed source code. Forking has not led to compatibility problems

RFB protocol is designed to be extensible VNC clients and servers negotiate their capabilities when

handshaking Make use of the most appropriate options supported at both ends

Etymology

Etymology

'Virtual Network Computer/Computing' Originates from ORL's work on a thin client called

the Videotile Used the RFB protocol

Essentially an LCD display with a pen input and a fast ATM connection to the network

At the time a network computer was commonly used as a synonym for 'thin client' VNC is essentially a software-only (i.e virtual) version of

this network computer

Operation

Operation

A VNC system consists of a client, a server, and a communication protocol. The VNC server

program on the machine that shares its screen The VNC client (or viewer)

Program that watches and interacts with the server The VNC protocol

Very simple, based on one graphic primitive: "Put a rectangle of pixel data at the specified X,Y

position".

Operation

Server sends small rectangles of the framebuffer to the client

In its simplest form, the VNC protocol can use a lot of bandwidth Methods devised to reduce communication overhead For example, various encodings

methods to determine the most efficient way to transfer these rectangles

VNC protocol allows the client and server to negotiate which encoding will be used

Operation

The simplest encoding is the raw encoding Pixel data is sent in left-to-right scanline order

Once the original full screen has been transmitted Only transfer rectangles that change

Supported by all clients and servers This encoding works well:

If only a small portion of the screen changes from one frame to the next Mouse pointer moving across a desktop Text being written at the cursor

Bandwidth demands get very high if a lot of pixels change at the same time Scrolling a window or viewing full-screen video

Operation

VNC by default uses TCP ports 5900 through 5906 each port corresponding to a separate screen (:0 to :6).

A Java viewer is available in many implementations Such as RealVNC allowing clients to interact through, among

other things, a Java-enabled web browser Ports 5800 through 5806

Other ports can be used Both client and server must be configured accordingly

Some operating systems only support a single VNC session at a time because the operating system supports only a single session at a time E.g. Windows XP

Operation

Note that on some machines, the server does not necessarily have to have a physical display. Xvnc is the Unix VNC server, which is based on a

standard X server Xvnc can be considered to be two servers in one; to

applications it is an X server, and to remote VNC users it is a VNC server

Applications can display themselves on Xvnc as if it were a normal X display Will appear on any connected VNC viewers rather than

on a physical screen

Operation

The display that is served by VNC Not necessarily the same display seen by a user on

the server Unix/Linux computers that support multiple

simultaneous X11 sessions VNC may be set to serve a particular existing X11

session Start one of its own

Multiple VNC sessions can be run from the same computer.

On Microsoft Windows the VNC session served is always the current user session

Operation

VNC is commonly used as a cross-platform remote desktop system Apple Remote Desktop for Mac OS X interoperates with

VNC Will connect to a Linux user's current desktop if it is served

with x11vnc As a separate X11 session if one is served with TightVNC

From Linux, TightVNC will connect to an OS X session served by Apple Remote Desktop if the VNC option is enabled, or to a VNC server running on Microsoft Windows

Security

Security

By default, VNC is not a secure protocol. Passwords are not sent in plain-text (as in telnet) but…

brute-force cracking could prove successful if both the encryption key and encoded password are sniffed from a network.

It is recommended that a password of at least 8 characters be used. There is also an 8-character limit on some versions of

VNC; If a password is sent exceeding 8 characters

Excess characters are removed Truncated string is compared to the password.

Security

VNC may be tunneled over an SSH or VPN connection Adds an extra security layer with stronger

encryption SSH clients are available for all major platforms

(and many smaller platforms as well); SSH tunnels can be created from

UNIX clients Microsoft Windows clients Macintosh clients many others

Security

UltraVNC supports the use of an open-source encryption plugin Encrypts the entire VNC session Including password authentication and data transfer

Allows authentication to be performed based on NTLM and Active Directory user accounts

RealVNC offers high-strength encryption as part of its commercial package

Workspot released AES encryption patches for VNC

The original

http://www.cl.cam.ac.uk/research/dtg/attarchive/vnc/index.html

RFB

http://en.wikipedia.org/wiki/RFB_protocol

RFB

RFB (“remote framebuffer”) is a simple protocol for remote access to graphical user interfaces It works at the framebuffer level

Applicable to all windowing systems and applications Including X11, Windows and Macintosh.

RFB is the protocol used in Virtual Network Computing (VNC) and its derivatives.

Although RFB started as a relatively simple protocol it has been enhanced with additional features (such as file transfers) and more sophisticated compression and security techniques as it has developed

To maintain seamless cross-compatibility between the many different VNC client and server implementations Clients and servers negotiate a connection using the best RFB

version Use the most appropriate compression and security options they can

both support.

History

RFB was originally developed at Olivetti Research Laboratory (ORL) A remote display technology to be used by a simple thin client

with ATM connectivity called a Videotile. In order to keep the device as simple as possible, RFB was

developed and used in preference to any of the existing remote display technologies.

RFB found a second, more enduring use when VNC was developed VNC was released as open source software and the RFB

specification published on the web. Since then RFB has been a free protocol which anybody can use.

When ORL was closed in 2002 some of the key people behind VNC and RFB formed RealVNC Ltd in order to continue development of VNC and to maintain the RFB protocol. The current RFB protocol is published on the RealVNC website.

Protocol versions

Published versions of the RFB protocol are shown below: Developers are free to add additional encoding and security types

Must book unique identification numbers for these with the maintainers of the protocol so that the numbers do not clash.

Clashing type numbers would cause confusion when handshaking a connection and break cross-compatibility between implementations

The list of encoding and security types is maintained by RealVNC Ltd Separate from the protocol specification New types can be added without requiring the specification to be reissued

Version Source Date Specification

RFB 3.3 ORL January 1998 The Remote Framebuffer Protocol 3.3

RFB 3.7 RealVNC Ltd July 2003

RFB 3.8 (current)

RealVNC Ltd July 2005 The Remote Framebuffer Protocol 3.8