MUNGE(7)						    MUNGE Uid 'N' Gid Emporium							  MUNGE(7)

NAME

       munge - MUNGE overview

INTRODUCTION

       MUNGE (MUNGE Uid 'N' Gid Emporium) is an authentication service for creating and validating credentials.  It is designed to be highly scal-
       able for use in an HPC cluster environment.  It allows a process to authenticate the UID and GID of another local or remote process  within
       a group of hosts having common users and groups.  These hosts form a security realm that is defined by a shared cryptographic key.  Clients
       within this security realm can create and validate credentials without the use of root privileges,  reserved  ports,  or  platform-specific
       methods.

RATIONALE

       The  need  for  MUNGE  arose  out  of  the  HPC cluster environment.  Consider the scenario in which a local daemon running on a login node
       receives a client request and forwards it on to remote daemons running on compute nodes within the cluster.  Since  the	user  has  already
       logged  on to the login node, the local daemon just needs a reliable means of ascertaining the UID and GID of the client process.  Further-
       more, the remote daemons need a mechanism to ensure the forwarded authentication data has not been subsequently altered.

       A common solution to this problem is to use Unix domain sockets to determine the identity of the local client, and then forward this infor-
       mation on to remote hosts via trusted rsh connections.  But this presents several new problems.	First, there is no portable API for deter-
       mining the identity of a client over a Unix domain socket.  Second, rsh connections must originate from a reserved port; the limited number
       of  reserved  ports  available  on  a  given  host  directly limits scalability.  Third, root privileges are required in order to bind to a
       reserved port.  Finally, the remote daemons have no means of determining whether the client identity is authentic.

USAGE

       A process creates a credential by requesting one from the local MUNGE service, either via the munge_encode() C library call  or	the  munge
       executable.   The  encoded  credential  contains  the UID and GID of the originating process.  This process sends the credential to another
       process within the security realm as a means of proving its identity.  The receiving process validates the credential with the use  of  its
       local MUNGE service, either via the munge_decode() C library call or the unmunge executable.  The decoded credential provides the receiving
       process with a reliable means of ascertaining the UID and GID of the originating process.  This information can be used for  accounting	or
       access control decisions.

DETAILS

       The contents of the credential (including any optional payload data) are encrypted with a key shared by all munged daemons within the secu-
       rity realm.  The integrity of the credential is ensured by a message authentication code (MAC).	The credential is valid for a limited time
       defined	by  its  time-to-live  (TTL);  this presumes clocks within a security realm are in sync.  Unexpired credentials are tracked by the
       local munged daemon in order to prevent replay attacks on a given host.	Decoding of a credential can be restricted to  a  particular  user
       and/or  group  ID.   The payload data can be used for purposes such as embedding the destination's address to ensure the credential is only
       valid on a specific host.  The internal format of the credential is encoded in a platform-independent manner.  And the credential itself is
       base64 encoded to allow it to be transmitted over virtually any transport.

AUTHOR

       Chris Dunlap <cdunlap@llnl.gov>

COPYRIGHT

       Copyright (C) 2007-2011 Lawrence Livermore National Security, LLC.
       Copyright (C) 2002-2007 The Regents of the University of California.

       MUNGE is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free
       Software Foundation, either version 3 of the License, or (at your option) any later version.

       Additionally for the MUNGE library (libmunge), you can redistribute it and/or modify it under the terms of the GNU  Lesser  General  Public
       License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

SEE ALSO

       munge(1), remunge(1), unmunge(1), munge(3), munge_ctx(3), munge_enum(3), munged(8).

       http://munge.googlecode.com/

munge-0.5.10							    2011-02-25								  MUNGE(7)