XSecurity man page on DigitalUNIX

Man page or keyword search:  
man Server   12896 pages
apropos Keyword Search (all sections)
Output format
DigitalUNIX logo
[printable version]

XSecurity(1X)							 XSecurity(1X)

NAME
       XSecurity, Xsecurity - X display access control

DESCRIPTION
       X  provides  mechanism  for  implementing  many access control systems.
       Release 6 includes five mechanisms:

       Host Access	     Simple host-based access control.
       MIT-MAGIC-COOKIE-1    Shared plain-text "cookies".
       XDM-AUTHORIZATION-1   Secure DES based private-keys.
       SUN-DES-1	     Based on Sun's secure rpc system.
       MIT-KERBEROS-5	     Kerberos Version 5 user-to-user.

ACCESS SYSTEM DESCRIPTIONS
       Any client on a host in the host access control list is allowed	access
       to  the	X server.  This system can work reasonably well in an environ‐
       ment where everyone trusts everyone, or when only a single  person  can
       log  in	to  a given machine, and is easy to use when the list of hosts
       used is small.  This system does not work well when multiple people can
       log in to a single machine and mutual trust does not exist. The list of
       allowed hosts is stored in the X server and can	be  changed  with  the
       xhost command.  When using the more secure mechanisms listed below, the
       host list is normally configured to be the empty	 list,	so  that  only
       authorized  programs can connect to the display.	 When using MIT-MAGIC-
       COOKIE-1, the client sends a 128 bit "cookie" along with the connection
       setup  information.  If	the cookie presented by the client matches one
       that the X server has, the connection is allowed access. The cookie  is
       chosen so that it is hard to guess; xdm generates such cookies automat‐
       ically when this form of access control is used.	 The  user's  copy  of
       the  cookie  is	usually	 stored	 in  the  file	in the home directory,
       although the environment variable XAUTHORITY can be used to specify  an
       alternate  location.   Xdm  automatically passes a cookie to the server
       for each new login session, and stores the cookie in the user  file  at
       login.

	      The  cookie is transmitted on the network without encryption, so
	      there is nothing to prevent a network snooper from obtaining the
	      data  and	 using it to gain access to the X server.  This system
	      is useful in an environment where many users are running	appli‐
	      cations  on the same machine and want to avoid interference from
	      each other, with the caveat that this control is only as good as
	      the  access  control  to	the  physical network. In environments
	      where network-level snooping is difficult, this system can  work
	      reasonably well.	Sites in the United States can use a DES-based
	      access control mechanism called XDM-AUTHORIZATION-1. It is simi‐
	      lar  in  usage  to MIT-MAGIC-COOKIE-1 in that a key is stored in
	      the file and is shared with the X server. However, this key con‐
	      sists of two parts -- a 56 bit DES encryption key and 64 bits of
	      random data used as the authenticator.

	      When connecting to the X server, the application	generates  192
	      bits  of	data  by  combining the current time in seconds (since
	      00:00 1/1/1970 GMT) along with 48	 bits  of  "identifier".   For
	      TCP/IP connections, the identifier is the address plus port num‐
	      ber; for local connections it is the process ID and 32  bits  to
	      form  a  unique  id  (in	case  multiple connections to the same
	      server are made from a single process).  This 192 bit packet  is
	      then encrypted using the DES key and sent to the X server, which
	      is able to verify if the requester is authorized to  connect  by
	      decrypting  with the same DES key and validating the authentica‐
	      tor and additional data. This system is useful in many  environ‐
	      ments where host-based access control is inappropriate and where
	      network security cannot be ensured.  Recent  versions  of	 SunOS
	      (and  some  other	 systems)  have	 included  a secure public key
	      remote procedure call system.   This  system  is	based  on  the
	      notion  of a network principal; a user name and NIS domain pair.
	      Using this system, the X server can securely discover the actual
	      user  name  of  the  requesting process.	It involves encrypting
	      data with the X server's public key, and so the identity of  the
	      user  who started the X server is needed for this; this identity
	      is stored in the file.  By  extending  the  semantics  of	 "host
	      address"	to include this notion of network principal, this form
	      of access control is very easy to use.

	      To allow access by a new user, use xhost.	 For example,

	      xhost keith@ ruth@mit.edu

	      adds "keith" from the NIS	 domain	 of  the  local	 machine,  and
	      "ruth"  in  the "mit.edu" NIS domain.  For keith or ruth to suc‐
	      cessfully connect to the display, they must  add	the  principal
	      who started the server to their file.  For example:

	      xauth	  add	    expo.lcs.mit.edu:0	     \	     SUN-DES-1
	      unix.expo.lcs.mit.edu@our.domain.edu

	      This system only works on machines which support Secure RPC, and
	      only  for users which have set up the appropriate public/private
	      key pairs on their system.  See the Secure RPC documentation for
	      details.	To access the display from a remote host, you may have
	      to do a keylogin on the remote host first.  Kerberos is  a  net‐
	      work-based  authentication  scheme  developed by MIT for Project
	      Athena.  It allows mutually suspicious principals	 to  authenti‐
	      cate  each other as long as each trusts a third party, Kerberos.
	      Each principal has a secret key known only to it	and  Kerberos.
	      Principals  includes servers, such as an FTP server or X server,
	      and human users, whose key is their password.  Users gain access
	      to  services by getting Kerberos tickets for those services from
	      a Kerberos server.  Since the X server has no place to  store  a
	      secret key, it shares keys with the user who logs in.  X authen‐
	      tication thus uses the user-to-user scheme of  Kerberos  version
	      5.

	      When  you	 log  in via xdm, xdm will use your password to obtain
	      the initial Kerberos tickets.  xdm stores the tickets in a  cre‐
	      dentials cache file and sets the environment variable KRB5CCNAME
	      to point to the file.  The credentials cache is  destroyed  when
	      the  session  ends  to  reduce  the  chance of the tickets being
	      stolen before they expire.

	      Since Kerberos is a user-based authorization protocol, like  the
	      SUN-DES-1	 protocol,  the owner of a display can enable and dis‐
	      able specific users, or Kerberos principals. The xhost client is
	      used to enable or disable authorization. For example,

	      xhost krb5:judy krb5:gildea@x.org

	      adds  "judy"  from  the Kerberos realm of the local machine, and
	      "gildea" from the "x.org" realm.

THE AUTHORIZATION FILE
       Except for Host Access control, each of these systems uses data	stored
       in  the	file to generate the correct authorization information to pass
       along to the X server at connection setup.  MIT-MAGIC-COOKIE-1 and XDM-
       AUTHORIZATION-1	store  secret data in the file; so anyone who can read
       the file can gain access to the X server.  SUN-DES-1  stores  only  the
       identity	 of the principal who started the server (unix.hostname@domain
       when the server is started by xdm), and so it is not useful  to	anyone
       not authorized to connect to the server.

       Each  entry  in	the  file matches a certain connection family (TCP/IP,
       DECnet or local connections) and X display name (hostname plus  display
       number).	 This allows multiple authorization entries for different dis‐
       plays to share the same data file.  A special connection family	(Fami‐
       lyWild,	value  65535) causes an entry to match every display, allowing
       the entry to be used for all connections.  Each entry additionally con‐
       tains the authorization name and whatever private authorization data is
       needed by that authorization type to generate the  correct  information
       at connection setup time.

       The  xauth  program  manipulates	 the  file  format. It understands the
       semantics of the connection families and	 address  formats,  displaying
       them  in	 an  easy to understand format.	 It also understands that SUN-
       DES-1 and MIT-KERBEROS-5 use string values for the authorization	 data,
       and displays them appropriately.

       The X server (when running on a workstation) reads authorization infor‐
       mation from a file name passed on  the  command	line  with  the	 -auth
       option (see the Xserver(1X) manual page).  The authorization entries in
       the file are used to control access to the  server.   In	 each  of  the
       authorization  schemes  listed  above, the data needed by the server to
       initialize an authorization scheme is identical to the data  needed  by
       the  client  to	generate the appropriate authorization information, so
       the same file can be used by both processes.  This system uses 128 bits
       of  data	 shared	 between  the user and the X server. Any collection of
       bits can be used.  Xdm generates these keys using  a  cryptographically
       secure  pseudo random number generator, and so the key to the next ses‐
       sion cannot be computed from the current session key.  This system uses
       two  pieces of information.  First, 64 bits of random data, second a 56
       bit DES encryption key (again, random data) stored in 8 bytes, the last
       byte of which is ignored.  Xdm generates these keys using the same ran‐
       dom number generator as is used for  MIT-MAGIC-COOKIE-1.	  This	system
       needs  a	 string	 representation	 of the principal which identifies the
       associated X server. This information is used to encrypt	 the  client's
       authority  information when it is sent to the X server. When xdm starts
       the X server, it uses the root principal for the machine on which it is
       running		 (unix.hostname@domain,		 for	      example,
       "unix.expire.lcs.mit.edu@our.domain.edu").  Putting the correct princi‐
       pal name in the file causes Xlib to generate the appropriate authoriza‐
       tion information using the secure RPC library.  Kerberos reads  tickets
       from  the  cache	 pointed to by the KRB5CCNAME environment variable, so
       does not use any data from the file.  An empty entry must  still	 exist
       to tell clients that MIT-KERBEROS-5 is available.

FILES
SEE ALSO
       X(1X), xdm(1X), xauth(1X), xhost(1X), Xserver(1X)

								 XSecurity(1X)
[top]

List of man pages available for DigitalUNIX

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net