KERBEROS(1)KERBEROS(1)NAMEkerberos - introduction to the Kerberos system
The Kerberos system authenticates individual users in a network envi‐
ronment. After authenticating yourself to Kerberos, you can use net‐
work 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 workstations 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
password. 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 message:
Principal unknown (kerberos)
you haven't been registered as a Kerberos user. See your system admin‐
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 running 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 corre‐
sponds to the Kerberos service providing authentication for the princi‐
pal. For example, at MIT there is a Kerberos running at the Laboratory
for Computer Science and one running at Project Athena.
When writing a Kerberos name, the principal name is separated 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 names:
When you authenticate yourself with Kerberos, through either the work‐
station toehold system or the kinit command, Kerberos gives you an ini‐
tial Kerberos ticket. (A Kerberos ticket is an encrypted protocol mes‐
sage that provides authentication.) Kerberos uses this ticket for net‐
work utilities such as rlogin and rcp. The ticket transactions 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 installation'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-authenticate
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 ses‐
sion. 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 commands,
see the kinit(1) and kdestroy(1) manual pages.
Currently, Kerberos supports the following network services: 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.
SEE ALSOkdestroy(1), kinit(1), klist(1), kpasswd(1), des_crypt(3), kerberos(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 net‐
work in clear text.
Steve Miller, MIT Project Athena/Digital Equipment Corporation
Clifford Neuman, MIT Project Athena
The following people helped out on various aspects of the system:
Jeff Schiller designed and wrote the administration server and its user
interface, kadmin. He also wrote the dbm version of the database man‐
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 userreg.
Stan Zanarotti pioneered Kerberos in a foreign realm (LCS), and made
many contributions based on that experience.
Many people contributed code and/or useful ideas, including 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 Win Treese.
COPYRIGHT 1985,1986 Massachusetts Institute of Technology
MIT Project Athena Kerberos Version 4.0 KERBEROS(1)