X Window

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X Window

• JianJing Cao

(ID 98284)
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Content

• Introduction
• X Window System
• Function
• Window Principle
• How X Window Works
• Security

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Introduction

• X window, a window system for UNIX was developed
  at M.I.T when graphics terminals came into
  existence
• The X Window system is device independent -- it
  can run on most common computer platforms. It
  includes workstations from companies such as Sun
  Microsystems Inc, and Silicon Graphics Inc.

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Introduction

• X window is a portable, network-transparent
  window system which runs on many different
  computers. It is frequently used in conjunction
  with the UNIX operating system
• X window is a client-server model

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X Window System
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X Window system


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Function

• X Window provides a consistent means of graphical
  user interaction for UNIX workstations.
• Motif (one of toolkit) uses X window provides an
  introduction to graphic user interface (GUI)
  programming base on Unix operating system.

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Function

• With X the programmer can write a single
  application in a single language and run this
  program on different machines with little or no
  modification. Moreover, applications can actually
  run programs on one computer and have the results
  displayed on another (or several) computer's
  terminal.

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X Window Principle

• All forms of displaying of information in X are
  bit-mapped
• X, like most other windowing systems, divides the
  screen into various parts that control input and
  output. Each part is called a window
• Not all applications need to consist of a single
  window.

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X Window Principle

• There is one special window, the background or
  root window. All other windows are children of
  the root .

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How X window Works

• It runs on a machine with a display, keyboard,
  and a mouse
• All a client program needs to do to use the X
  display is to open up a connection with the
  server and then send Protocol requests to it.

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How X window works

• There are 4 types of messages passing between the
  client and server
• Requests - the client can ask the server to draw
  something, or ask for information.
• Replies - the server can reply.
• Events - the server can supervise the client with
  something
• Errors - the server can report an error

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Security

• Problem
• Solution

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Damage Possible By Attacker

• destroy any (or all) of your windows
• open new windows on your screen
• view the contents of your screen remotely
• log all keystrokes, including passwords, typed
  while in X

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Damage Possible By Attacker

• generate spurious X events causing arbitrary
  instructions to be executed (this risk is
  particularly great if you use Emacs)

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Solution

• Host Authentication
• Token Authentication

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Host Authentication

• Using xhost(display,add,move)

Benfit The xhost access control mechanism
is certainly easy to use. A
single program with a simple syntax is
required Drawbacks 1.Many environments, where
numerous users are
allowed access to a particular host .
2. NCD servers, SGI systems, and Mac X
for the Macintosh come
with access control disable
by default.
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Token Authentication

• xauth Program The xauth program is used for
  editing and displaying the user's magic cookie
  authorization information
• The X Display Manager xdm, is a client which
  provides login screens for multiple X Servers

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Token Authentication

• Benefits Authorization is now done on a
  user-by-user basis, not a host-by-host basis.
• Drawbacks The xdm and xauth programs are time
  consuming for both the administrator and the end
  user to use and maintain. They require a good
  understanding of the X client-server model on the
  part of the user.

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Reference

• http//search.yahoo.com/bin/search?pXwindow
• Structure Computer Organization 4th Edition
  Andrew S. Tanenbaum

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END