KERBEROS

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:

kinit(v5): Client not found in Kerberos database while getting initial credentials

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:

        david
        jennifer/admin
        joeuser@BLEEP.COM
        cbrown/root@FUBAR.ORG

When you authenticate yourself with Kerberos you get an initial Kerberos ticket. (A Kerberos 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 Kerberos 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 forwardable 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 1985,1986,1989-1996,2002 Massachusetts Institute of Technology