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 scalable 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. Furthermore, 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
information on to remote hosts via trusted rsh connections. But this
presents several new problems. First, there is no portable API for
determining 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.
OVERVIEW
A process creates a credential by requesting one from the local MUNGE
service. 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. 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.
The contents of the credential (including any optional payload data)
are encrypted with a key shared by all munged daemons within the security 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). The daemon ensures unexpired credentials are not replayed on a particular 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) 2007-2010 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://home.gna.org/munge/