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kerberos - introduction to the Kerberos system
The Kerberos system authenticates individual users in a
network environment. After authenticating yourself to
Kerberos, you can use network utilities such as rlogin,
rcp, and rsh without having to present passwords to remote
hosts and without having to bother with .rhosts files.
Note that these utilities will work without passwords only
if the remote machines you deal with support the Kerberos
system. All Athena timesharing machines and public work-
stations support Kerberos.
Before you can use Kerberos, you must register as an
Athena user, and you must make sure you have been added to
the Kerberos database. You can use the kinit command to
find out. This command tries to log you into the Kerberos
system. kinit will prompt you for a username and pass-
word. Enter your username and password. If the utility
lets you login without giving you a message, you have
already been registered.
If you enter your username and kinit responds with this
Principal unknown (kerberos)
you haven't been registered as a Kerberos user. See your
A Kerberos name contains three parts. The first is the
principal name, which is usually a user's or service's
name. The second is the instance, which in the case of a
user is usually null. Some users may have privileged
instances, however, such as ``root'' or ``admin''. In the
case of a service, the instance is the name of the machine
on which it runs; i.e. there can be an rlogin service run-
ning on the machine ABC, which is different from the
rlogin service running on the machine XYZ. The third part
of a Kerberos name is the realm. The realm corresponds to
the Kerberos service providing authentication for the
principal. For example, at MIT there is a Kerberos run-
ning at the Laboratory for Computer Science and one run-
ning at Project Athena.
When writing a Kerberos name, the principal name is sepa-
rated from the instance (if not null) by a period, and the
realm (if not the local realm) follows, preceded by an
``@'' sign. The following are examples of valid Kerberos
MIT Project Athena Kerberos Version 4.0 1
When you authenticate yourself with Kerberos, through
either the workstation toehold system or the kinit com-
mand, Kerberos gives you an initial Kerberos ticket. (A
Kerberos ticket is an encrypted protocol message that pro-
vides authentication.) Kerberos uses this ticket for net-
work utilities such as rlogin and rcp. The ticket trans-
actions are done transparently, so you don't have to worry
about their management.
Note, however, that tickets expire. Privileged tickets,
such as root instance tickets, expire in a few minutes,
while tickets that carry more ordinary privileges may be
good for several hours or a day, depending on the instal-
lation's policy. If your login session extends beyond the
time limit, you will have to re-authenticate yourself to
Kerberos to get new tickets. Use the kinit command to re-
If you use the kinit command to get your tickets, make
sure you use the kdestroy command to destroy your tickets
before you end your login session. You should probably
put the kdestroy command in your .logout file so that your
tickets will be destroyed automatically when you logout.
For more information about the kinit and kdestroy com-
mands, see the kinit(1) and kdestroy(1) manual pages.
Currently, Kerberos supports the following network ser-
vices: rlogin, rsh, and rcp. Other services are being
worked on, such as the pop mail system and NFS (network
file system), but are not yet available.
kdestroy(1), kinit(1), klist(1), kpasswd(1), des_crypt(3),
Kerberos will not do authentication forwarding. In other
words, if you use rlogin to login to a remote host, you
cannot use Kerberos services from that host until you
authenticate yourself explicitly on that host. Although
you may need to authenticate yourself on the remote host,
be aware that when you do so, rlogin sends your password
across the network in clear text.
Steve Miller, MIT Project Athena/Digital Equipment Corpo-
Clifford Neuman, MIT Project Athena
MIT Project Athena Kerberos Version 4.0 2
The following people helped out on various aspects of the
Jeff Schiller designed and wrote the administration server
and its user interface, kadmin. He also wrote the dbm
version of the database management system.
Mark Colan developed the Kerberos versions of rlogin, rsh,
and rcp, as well as contributing work on the servers.
John Ostlund developed the Kerberos versions of passwd and
Stan Zanarotti pioneered Kerberos in a foreign realm
(LCS), and made many contributions based on that experi-
Many people contributed code and/or useful ideas, includ-
ing Jim Aspnes, Bob Baldwin, John Barba, Richard Basch,
Jim Bloom, Bill Bryant, Rob French, Dan Geer, David
Jedlinsky, John Kohl, John Kubiatowicz, Bob McKie, Brian
Murphy, Ken Raeburn, Chris Reed, Jon Rochlis, Mike
Shanzer, Bill Sommerfeld, Jennifer Steiner, Ted Ts'o, and
COPYRIGHT 1985,1986 Massachusetts Institute of Technology
MIT Project Athena Kerberos Version 4.0 3
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.
(Corrections, notes, and links courtesy of RocketAware.com)
FreeBSD Sources for kerberos(8)
OpenBSD sources for kerberos(8)
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