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.
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 administrator.
A Kerberos name usually contains three parts. The first is the primary, 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 fully qualified 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 corresponds to the Kerberos service providing
authentication for the principal.
When writing a Kerberos name, the principal name is separated from the instance (if not
null) by a slash, 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 you get an initial Kerberos ticket. (A Ker-
beros ticket is an encrypted protocol message that provides authentication.) Kerberos
uses this ticket for network 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 those with the instance
``root'', 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 Ker-
beros to get new tickets. Use the kinit command to re-authenticate yourself.
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 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.
Kerberos tickets can be forwarded. In order to forward tickets, you must request forward-
able tickets when you kinit. Once you have forwardable tickets, most Kerberos programs
have a command line option to forward them to the remote host.
Currently, Kerberos support is available for the following network services: rlogin, rsh,
rcp, telnet, ftp, krdist (a Kerberized version of rdist), ksu (a Kerberized version of
su), login, and Xdm.
kdestroy(1), kinit(1), klist(1), kpasswd(1), rsh(1), rcp(1), rlogin(1), telnet(1),
ftp(1), krdist(1), ksu(1), sclient(1), xdm(1), des_crypt(3), hash(3), krb5strings(3),
krb5.conf(5), kdc.conf(5), kadmin(8), kadmind(8), kdb5_util(8), telnetd(8), ftpd(8),
rdistd(8), sserver(8), klogind(8c), kshd(8c), login(8c)
Steve Miller, MIT Project Athena/Digital Equipment Corporation
Clifford Neuman, MIT Project Athena
Kerberos was developed at MIT. OpenVision rewrote and donated the administration server,
which is used in the current version of Kerberos 5.
Copyright 1985,1986,1989-1996 Massachusetts Institute of Technology