KERBEROS(8)

NAME
kerberos - introduction to the Kerberos system

DESCRIPTION
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 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 administrator.

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 corresponds to the Kerberos service providing authentication for the principal. 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:

billb
jis.admin
srz@lcs.mit.edu
treese.root@athena.mit.edu

When you authenticate yourself with Kerberos, through either the workstation toehold system or the kinit command, Kerberos gives you 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 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 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 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 ALSO
kdestroy(1), kinit(1), klist(1), kpasswd(1), des_crypt(3), kerberos(3), kadmin(8)

BUGS
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.

AUTHORS
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 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 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.

RESTRICTIONS
COPYRIGHT 1985,1986 Massachusetts Institute of Technology