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VNC

VNC. http://en.wikipedia.org/wiki/Vnc. VNC demo. Windows TightVNC 10.18.199.185 Ubuntu Gtk VNC Viewer. VNC. Virtual Network Computing. VNC - Overview. Virtual Network Computing ( VNC ) A graphical desktop sharing system Uses the RFB protocol Remotely “control” another computer

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VNC

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

  2. VNC demo • Windows • TightVNC • 10.18.199.185 • Ubuntu • Gtk VNC Viewer

  3. VNC Virtual Network Computing

  4. VNC - Overview • Virtual Network Computing (VNC) • A graphical desktop sharing system • Uses the RFB protocol • Remotely “control” another computer • Use another computer via a GUI environment • Uses a network • Transmit keyboard and mouse events from one computer to another • Relays the graphical screen updates back

  5. 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

  6. VNC - Overview • Developed at AT&T • Original VNC source code and many modern derivatives are: • Open source • GNU General Public License

  7. History

  8. 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 • Continued 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

  9. Etymology

  10. Etymology • 'Virtual Network Computer/Computing' • Originates from ORL's work on a thin client • Called Videotile • Used the RFB protocol • Essentially an LCD display with: • A pen input • 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

  11. Operation

  12. Operation • VNC system requires: • A server • A client • A communication protocol

  13. Operation • Where: • VNC server • Program on the machine that shares its “screen” • Does all the core processing • VNC client (or viewer) • Program that monitors and interacts with the server • Displays results • VNC protocol • Very simple protocol • Based on one graphic primitive: • "Put a rectangle of pixel data at the specified X,Y position"

  14. Operation • Server sends small rectangles of the framebuffer to the client • In simplest form: 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 rectangles • VNC protocol • Allows client and server to negotiate which encoding to be used

  15. Operation • Simplest encoding: raw encoding • Pixel data is sent in left-to-right scanline order • First sends complete image • After original full screen has been transmitted • Only transfer rectangles that change • Supported by all clients and servers • Raw Encoding works well if: • Only a small portion of the screen changes from frame to frame • Mouse pointer moving across a desktop • Text being written at the cursor • Bandwidth demands get very high when a lot of pixels change at the same time • Scrolling a window • Viewing full-screen video

  16. Operation • VNC uses TCP ports 5900 through 5906 (default) • Each port corresponds to a separate screen (:0 to :6) • Java viewer available for many implementations • RealVNC allows clients to interact through 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 • Base operating system supports only a single session at a time • E.g. Windows XP

  17. Operation • On some machines: • Server does not have to have a physical display • Xvnc is the Unix VNC server • Based on a standard X server • Xvnc can be considered to be two servers in one • to applications: it is an X server • 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

  18. Operation • Display 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 • Microsoft Windows • VNC session served is always current user session

  19. 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 • VNC server running on Microsoft Windows

  20. Security

  21. 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 • Recommended that a password of at least 8 characters be used • Limit of 8-characters on some versions of VNC • If a password exceeds 8 characters: • Excess characters are removed • Truncated string is compared to the password

  22. 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

  23. 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

  24. The original • http://www.cl.cam.ac.uk/research/dtg/attarchive/

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

  26. Remote Frame Buffer RFB

  27. RFB • RFB (“remote framebuffer”) • A simple protocol for remote access to graphical user interfaces • Works at the framebuffer level • Applicable to all windowing systems and applications • Including X11, Windows and Macintosh • Used in Virtual Network Computing (VNC) and its derivatives • RFB started as a relatively simple protocol • 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 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

  28. History • RFB was originally developed at Olivetti Research Laboratory • Remote display technology • used by a simple thin client with ATM connectivity called a Videotile • To keep the device as simple as possible • RFB was developed and used in preference of 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. • ORL was closed in 2002 • Some key people behind VNC and RFB formed RealVNC Ltd • Continued development of VNC • Maintain the RFB protocol • Current RFB protocol is published on the RealVNC website

  29. 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

  30. Encoding • Pixel data can be encoded to compress data • Raw • Hextile • Zlib • Many others… • Can reduce the amount of data sent • Various encoding have different efficiencies • Can vary by screen content • Has a cost of the time to encode/decode • Note: encoding is NOT encrypting!

  31. Encoding

  32. VNC • Uses a desktop on the client • Displays an image of a server “desktop” on the client • Is, by default, secure • Should never be used on modern computers

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