Copyright © 1985-2007 by the Massachusetts Institute of Technology.
Export of software employing encryption from the United States of America may require a specific license from the United States Government. It is the responsibility of any person or organization contemplating export to obtain such a license before exporting.
WITHIN THAT CONSTRAINT, permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of M.I.T. not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. Furthermore if you modify this software you must label your software as modified software and not distribute it in such a fashion that it might be confused with the original MIT software. M.I.T. makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.
Individual source code files are copyright MIT, Cygnus Support, Novell, OpenVision Technologies, Oracle, Red Hat, Sun Microsystems, FundsXpress, and others.
Project Athena, Athena, Athena MUSE, Discuss, Hesiod, Kerberos, Moira, and Zephyr are trademarks of the Massachusetts Institute of Technology (MIT). No commercial use of these trademarks may be made without prior written permission of MIT.
"Commercial use" means use of a name in a product or other for-profit manner. It does NOT prevent a commercial firm from referring to the MIT trademarks in order to convey information (although in doing so, recognition of their trademark status should be given).
The following copyright and permission notice applies to the
OpenVision Kerberos Administration system located in
kadmin/create, kadmin/dbutil, kadmin/passwd,
kadmin/server, lib/kadm5, and portions of
lib/rpc:
Copyright, OpenVision Technologies, Inc., 1996, All Rights ReservedWARNING: Retrieving the OpenVision Kerberos Administration system source code, as described below, indicates your acceptance of the following terms. If you do not agree to the following terms, do not retrieve the OpenVision Kerberos administration system.
You may freely use and distribute the Source Code and Object Code compiled from it, with or without modification, but this Source Code is provided to you "AS IS" EXCLUSIVE OF ANY WARRANTY, INCLUDING, WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, OR ANY OTHER WARRANTY, WHETHER EXPRESS OR IMPLIED. IN NO EVENT WILL OPENVISION HAVE ANY LIABILITY FOR ANY LOST PROFITS, LOSS OF DATA OR COSTS OF PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, OR FOR ANY SPECIAL, INDIRECT, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THIS AGREEMENT, INCLUDING, WITHOUT LIMITATION, THOSE RESULTING FROM THE USE OF THE SOURCE CODE, OR THE FAILURE OF THE SOURCE CODE TO PERFORM, OR FOR ANY OTHER REASON.
OpenVision retains all copyrights in the donated Source Code. OpenVision also retains copyright to derivative works of the Source Code, whether created by OpenVision or by a third party. The OpenVision copyright notice must be preserved if derivative works are made based on the donated Source Code.
OpenVision Technologies, Inc. has donated this Kerberos Administration system to MIT for inclusion in the standard Kerberos 5 distribution. This donation underscores our commitment to continuing Kerberos technology development and our gratitude for the valuable work which has been performed by MIT and the Kerberos community.
Portions contributed by Matt Crawford <crawdad@fnal.gov> were work
performed at Fermi National Accelerator Laboratory, which is operated
by Universities Research Association, Inc., under contract
DE-AC02-76CHO3000 with the U.S. Department of Energy.
Portions of src/lib/crypto have the following copyright:
Copyright © 1998 by the FundsXpress, INC.All rights reserved.
Export of this software from the United States of America may require a specific license from the United States Government. It is the responsibility of any person or organization contemplating export to obtain such a license before exporting.
WITHIN THAT CONSTRAINT, permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of FundsXpress. not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. FundsXpress makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.
THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
The implementation of the Yarrow pseudo-random number generator
in src/lib/crypto/yarrow has the following copyright:
Copyright 2000 by Zero-Knowledge Systems, Inc.Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of Zero-Knowledge Systems, Inc. not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. Zero-Knowledge Systems, Inc. makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.
ZERO-KNOWLEDGE SYSTEMS, INC. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL ZERO-KNOWLEDGE SYSTEMS, INC. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTUOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
The implementation of the AES encryption algorithm in
src/lib/crypto/aes has the following copyright:
Copyright © 2001, Dr Brian Gladman<brg@gladman.uk.net>, Worcester, UK.
All rights reserved.LICENSE TERMS
The free distribution and use of this software in both source and binary form is allowed (with or without changes) provided that:
- distributions of this source code include the above copyright notice, this list of conditions and the following disclaimer;
- distributions in binary form include the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other associated materials;
- the copyright holder's name is not used to endorse products built using this software without specific written permission.
DISCLAIMER
This software is provided 'as is' with no explcit or implied warranties in respect of any properties, including, but not limited to, correctness and fitness for purpose.
Portions contributed by Red Hat, including the pre-authentication plug-in framework, contain the following copyright:
Copyright © 2006 Red Hat, Inc.
Portions copyright © 2006 Massachusetts Institute of Technology
All Rights Reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
- Neither the name of Red Hat, Inc., nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
The implementations of GSSAPI mechglue in GSSAPI-SPNEGO in
src/lib/gssapi, including the following files:
lib/gssapi/generic/gssapi_err_generic.et
lib/gssapi/mechglue/g_accept_sec_context.c
lib/gssapi/mechglue/g_acquire_cred.c
lib/gssapi/mechglue/g_canon_name.c
lib/gssapi/mechglue/g_compare_name.c
lib/gssapi/mechglue/g_context_time.c
lib/gssapi/mechglue/g_delete_sec_context.c
lib/gssapi/mechglue/g_dsp_name.c
lib/gssapi/mechglue/g_dsp_status.c
lib/gssapi/mechglue/g_dup_name.c
lib/gssapi/mechglue/g_exp_sec_context.c
lib/gssapi/mechglue/g_export_name.c
lib/gssapi/mechglue/g_glue.c
lib/gssapi/mechglue/g_imp_name.c
lib/gssapi/mechglue/g_imp_sec_context.c
lib/gssapi/mechglue/g_init_sec_context.c
lib/gssapi/mechglue/g_initialize.c
lib/gssapi/mechglue/g_inquire_context.c
lib/gssapi/mechglue/g_inquire_cred.c
lib/gssapi/mechglue/g_inquire_names.c
lib/gssapi/mechglue/g_process_context.c
lib/gssapi/mechglue/g_rel_buffer.c
lib/gssapi/mechglue/g_rel_cred.c
lib/gssapi/mechglue/g_rel_name.c
lib/gssapi/mechglue/g_rel_oid_set.c
lib/gssapi/mechglue/g_seal.c
lib/gssapi/mechglue/g_sign.c
lib/gssapi/mechglue/g_store_cred.c
lib/gssapi/mechglue/g_unseal.c
lib/gssapi/mechglue/g_userok.c
lib/gssapi/mechglue/g_utils.c
lib/gssapi/mechglue/g_verify.c
lib/gssapi/mechglue/gssd_pname_to_uid.c
lib/gssapi/mechglue/mglueP.h
lib/gssapi/mechglue/oid_ops.c
lib/gssapi/spnego/gssapiP_spnego.h
lib/gssapi/spnego/spnego_mech.c
are subject to the following license:
Copyright © 2004 Sun Microsystems, Inc.Kerberos V5 includes documentation and software developed at the University of California at Berkeley, which includes this copyright notice:Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
Copyright © 1983 Regents of the University of California.
All rights reserved.Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
- Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Portions contributed by Novell, Inc., including the LDAP database backend, are subject to the following license:
Copyright (c) 2004-2005, Novell, Inc. All rights reserved.Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
- The copyright holder's name is not used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notices and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions.
Kerberos V5 is an authentication system developed at MIT. Kerberos is named for the three-headed watchdog from Greek mythology, who guarded the entrance to the underworld.
Under Kerberos, a client (generally either a user or a service) sends a request for a ticket to the Key Distribution Center (KDC). The KDC creates a ticket-granting ticket (TGT) for the client, encrypts it using the client's password as the key, and sends the encrypted TGT back to the client. The client then attempts to decrypt the TGT, using its password. If the client successfully decrypts the TGT (i.e., if the client gave the correct password), it keeps the decrypted TGT, which indicates proof of the client's identity.
The TGT, which expires at a specified time, permits the client to obtain additional tickets, which give permission for specific services. The requesting and granting of these additional tickets is user-transparent.
Since Kerberos negotiates authenticated, and optionally encrypted, communications between two points anywhere on the internet, it provides a layer of security that is not dependent on which side of a firewall either client is on. Since studies have shown that half of the computer security breaches in industry happen from inside firewalls, MIT's Kerberos V5 plays a vital role in maintaining your network security.
The Kerberos V5 package is designed to be easy to use. Most of the commands are nearly identical to UNIX network programs you already use. Kerberos V5 is a single-sign-on system, which means that you have to type your password only once per session, and Kerberos does the authenticating and encrypting transparently.
Your Kerberos credentials, or "tickets", are a set of electronic information that can be used to verify your identity. Your Kerberos tickets may be stored in a file, or they may exist only in memory.
The first ticket you obtain is a ticket-granting ticket, which permits you to obtain additional tickets. These additional tickets give you permission for specific services. The requesting and granting of these additional tickets happens transparently.
A good analogy for the ticket-granting ticket is a three-day ski pass that is good at four different resorts. You show the pass at whichever resort you decide to go to (until it expires), and you receive a lift ticket for that resort. Once you have the lift ticket, you can ski all you want at that resort. If you go to another resort the next day, you once again show your pass, and you get an additional lift ticket for the new resort. The difference is that the Kerberos V5 programs notice that you have the weekend ski pass, and get the lift ticket for you, so you don't have to perform the transactions yourself.
A Kerberos principal is a unique identity to which Kerberos can assign tickets. Principals can have an arbitrary number of components. Each component is separated by a component separator, generally `/'. The last component is the realm, separated from the rest of the principal by the realm separator, generally `@'. If there is no realm component in the principal, then it will be assumed that the principal is in the default realm for the context in which it is being used.
Traditionally, a principal is divided into three parts: the
primary, the instance, and the realm. The format of
a typical Kerberos V5 principal is primary/instance@REALM.
host.
/). In the case of a user, the instance is usually null, but a
user might also have an additional principal, with an instance called
admin, which he/she uses to administrate a database. The
principal jennifer@ATHENA.MIT.EDU is completely
separate from the principal
jennifer/admin@ATHENA.MIT.EDU, with a separate
password, and separate permissions. In the case of a host, the instance
is the fully qualified hostname, e.g.,
daffodil.mit.edu.
daffodil.example.com would be in
the realm EXAMPLE.COM.
This tutorial is intended to familiarize you with the Kerberos V5
client programs. We will represent your prompt as "shell%".
So an instruction to type the "ls" command would be represented as
follows:
shell% ls
In these examples, we will use sample usernames, such as
jennifer and david, sample
hostnames, such as daffodil and
trillium, and sample domain names, such as
mit.edu and example.com. When you
see one of these, substitute your username, hostname, or domain name
accordingly.
Your system administrator will have installed the Kerberos V5
programs in whichever directory makes the most sense for your system.
We will use /usr/local throughout this guide to refer to the
top-level directory Kerberos V5 directory. We will therefor use
/usr/local/bin to denote the location of the Kerberos V5 user
programs. In your installation, the directory name may be different,
but whatever the directory name is, you should make sure it is included
in your path. You will probably want to put it ahead of the
directories /bin and /usr/bin so you will get the
Kerberos V5 network programs, rather than the standard UNIX
versions, when you type their command names.
On many systems, Kerberos is built into the login program, and you get
tickets automatically when you log in. Other programs, such as
rsh, rcp, telnet, and rlogin, can forward
copies of your tickets to the remote host. Most of these programs also
automatically destroy your tickets when they exit. However,
MIT recommends that you explicitly destroy your Kerberos
tickets when you are through with them, just to be sure. One way to
help ensure that this happens is to add the kdestroy command to
your .logout file. Additionally, if you are going to be away
from your machine and are concerned about an intruder using your
permissions, it is safest to either destroy all copies of your tickets,
or use a screensaver that locks the screen.
There are various properties that Kerberos tickets can have:
If a ticket is forwardable, then the KDC can issue a new ticket with a different network address based on the forwardable ticket. This allows for authentication forwarding without requiring a password to be typed in again. For example, if a user with a forwardable TGT logs into a remote system, the KDC could issue a new TGT for that user with the network address of the remote system, allowing authentication on that host to work as though the user were logged in locally.
When the KDC creates a new ticket based on a forwardable ticket, it sets the forwarded flag on that new ticket. Any tickets that are created based on a ticket with the forwarded flag set will also have their forwarded flags set.
A proxiable ticket is similar to a forwardable ticket in that it allows a service to take on the identity of the client. Unlike a forwardable ticket, however, a proxiable ticket is only issued for specific services. In other words, a ticket-granting ticket cannot be issued based on a ticket that is proxiable but not forwardable.
A proxy ticket is one that was issued based on a proxiable ticket.
A postdated ticket is issued with the invalid flag set. After the starting time listed on the ticket, it can be presented to the KDC to obtain valid tickets.
Tickets with the postdateable flag set can be used to issue postdated tickets.
Renewable tickets can be used to obtain new session keys without the user entering their password again. A renewable ticket has two expiration times. The first is the time at which this particular ticket expires. The second is the latest possible expiration time for any ticket issued based on this renewable ticket.
A ticket with the initial flag set was issued based on the authentication protocol, and not on a ticket-granting ticket. Clients that wish to ensure that the user's key has been recently presented for verification could specify that this flag must be set to accept the ticket.
An invalid ticket must be rejected by application servers. Postdated tickets are usually issued with this flag set, and must be validated by the KDC before they can be used.
A preauthenticated ticket is one that was only issued after the client requesting the ticket had authenticated itself to the KDC.
The hardware authentication flag is set on a ticket which required the use of hardware for authentication. The hardware is expected to be possessed only by the client which requested the tickets.
If a ticket has the transit policy checked flag set, then the KDC that issued this ticket implements the transited-realm check policy and checked the transited-realms list on the ticket. The transited-realms list contains a list of all intermediate realms between the realm of the KDC that issued the first ticket and that of the one that issued the current ticket. If this flag is not set, then the application server must check the transited realms itself or else reject the ticket.
The okay as delegate flag indicates that the server specified in the ticket is suitable as a delegate as determined by the policy of that realm. A server that is acting as a delegate has been granted a proxy or a forwarded TGT. This flag is a new addition to the Kerberos V5 protocol and is not yet implemented on MIT servers.
An anonymous ticket is one in which the named principal is a generic principal for that realm; it does not actually specify the individual that will be using the ticket. This ticket is meant only to securely distribute a session key. This is a new addition to the Kerberos V5 protocol and is not yet implemented on MIT servers.
If your site is using the Kerberos V5 login program, you will get
Kerberos tickets automatically when you log in. If your site uses a
different login program, you may need to explicitly obtain your Kerberos
tickets, using the kinit program. Similarly, if your Kerberos
tickets expire, use the kinit program to obtain new ones.
To use the kinit program, simply type kinit and then type
your password at the prompt. For example, Jennifer (whose username is
jennifer) works for Bleep, Inc. (a fictitious company
with the domain name mit.edu and the Kerberos realm
ATHENA.MIT.EDU). She would type:
shell% kinit
Password for jennifer@ATHENA.MIT.EDU: <-- [Type jennifer's password here.]
shell%
If you type your password incorrectly, kinit will give you the following error message:
shell% kinit
Password for jennifer@ATHENA.MIT.EDU: <-- [Type the wrong password here.]
kinit: Password incorrect
shell%
and you won't get Kerberos tickets.
Notice that kinit assumes you want tickets for your own
username in your default realm.
Suppose Jennifer's friend David is visiting, and he wants to borrow a
window to check his mail. David needs to get tickets for himself in his
own realm, EXAMPLE.COM.1 He would type:
shell% kinit david@EXAMPLE.COM
Password for david@EXAMPLE.COM: <-- [Type david's password here.]
shell%
David would then have tickets which he could use to log onto his own machine. Note that he typed his password locally on Jennifer's machine, but it never went over the network. Kerberos on the local host performed the authentication to the KDC in the other realm.
If you want to be able to forward your tickets to another host, you need to request forwardable tickets. You do this by specifying the -f option:
shell% kinit -f
Password for jennifer@ATHENA.MIT.EDU: <-- [Type your password here.]
shell%
Note that kinit does not tell you that it obtained forwardable
tickets; you can verify this using the klist command
(see Viewing Your Tickets with klist).
Normally, your tickets are good for your system's default ticket
lifetime, which is ten hours on many systems. You can specify a
different ticket lifetime with the -l option. Add the letter
s to the value for seconds, m for minutes, h for
hours, or d for days.
For example, to obtain forwardable tickets for
david@EXAMPLE.COM that would be good for
three hours, you would type:
shell% kinit -f -l 3h david@EXAMPLE.COM
Password for david@EXAMPLE.COM: <-- [Type david's password here.]
shell%
You cannot mix units; specifying a lifetime of 3h30m would result
in an error. Note also that most systems specify a maximum ticket
lifetime. If you request a longer ticket lifetime, it will be
automatically truncated to the maximum lifetime.
The klist command shows your tickets. When you first obtain
tickets, you will have only the ticket-granting ticket. (See What is a Ticket?.) The listing would look like this:
shell% klist
Ticket cache: /tmp/krb5cc_ttypa
Default principal: jennifer@ATHENA.MIT.EDU
Valid starting Expires Service principal
06/07/04 19:49:21 06/08/04 05:49:19 krbtgt/ATHENA.MIT.EDU@ATHENA.MIT.EDU
shell%
The ticket cache is the location of your ticket file. In the above
example, this file is named /tmp/krb5cc_ttypa. The default
principal is your kerberos principal. (see What is a Kerberos Principal?)
The "valid starting" and "expires" fields describe the period of
time during which the ticket is valid. The service principal
describes each ticket. The ticket-granting ticket has the primary
krbtgt, and the instance is the realm name.
Now, if jennifer connected to the machine
daffodil.mit.edu, and then typed
klist again, she would have gotten the following result:
shell% klist
Ticket cache: /tmp/krb5cc_ttypa
Default principal: jennifer@ATHENA.MIT.EDU
Valid starting Expires Service principal
06/07/04 19:49:21 06/08/04 05:49:19 krbtgt/ATHENA.MIT.EDU@ATHENA.MIT.EDU
06/07/04 20:22:30 06/08/04 05:49:19 host/daffodil.mit.edu@ATHENA.MIT.EDU
shell%
Here's what happened: when jennifer used telnet to connect
to the host daffodil.mit.edu, the telnet
program presented her ticket-granting ticket to the KDC and requested a
host ticket for the host
daffodil.mit.edu. The KDC sent the host
ticket, which telnet then presented to the host
daffodil.mit.edu, and she was allowed to
log in without typing her password.
Suppose your Kerberos tickets allow you to log into a host in another
domain, such as trillium.example.com, which
is also in another Kerberos realm, EXAMPLE.COM. If you
telnet to this host, you will receive a ticket-granting ticket for the
realm EXAMPLE.COM, plus the new host ticket for
trillium.example.com. klist will now
show:
shell% klist
Ticket cache: /tmp/krb5cc_ttypa
Default principal: jennifer@ATHENA.MIT.EDU
Valid starting Expires Service principal
06/07/04 19:49:21 06/08/04 05:49:19 krbtgt/ATHENA.MIT.EDU@ATHENA.MIT.EDU
06/07/04 20:22:30 06/08/04 05:49:19 host/daffodil.mit.edu@ATHENA.MIT.EDU
06/07/04 20:24:18 06/08/04 05:49:19 krbtgt/EXAMPLE.COM@ATHENA.MIT.EDU
06/07/04 20:24:18 06/08/04 05:49:19 host/trillium.example.com@ATHENA.MIT.EDU
shell%
You can use the -f option to view the flags that apply to
your tickets. The flags are:
Here is a sample listing. In this example, the user jennifer
obtained her initial tickets (I), which are forwardable
(F) and postdated (d) but not yet validated (i).
(See kinit Reference, for more information about postdated tickets.)
shell% klist -f
Ticket cache: /tmp/krb5cc_320
Default principal: jennifer@ATHENA.MIT.EDU
Valid starting Expires Service principal
31/07/05 19:06:25 31/07/05 19:16:25 krbtgt/ATHENA.MIT.EDU@ATHENA.MIT.EDU
Flags: FdiI
shell%
In the following example, the user david's tickets were
forwarded (f) to this host from another host. The tickets are
reforwardable (F).
shell% klist -f
Ticket cache: /tmp/krb5cc_p11795
Default principal: david@EXAMPLE.COM
Valid starting Expires Service principal
07/31/05 11:52:29 07/31/05 21:11:23 krbtgt/EXAMPLE.COM@EXAMPLE.COM
Flags: Ff
07/31/05 12:03:48 07/31/05 21:11:23 host/trillium.example.com@EXAMPLE.COM
Flags: Ff
shell%
Your Kerberos tickets are proof that you are indeed yourself, and tickets can be stolen. If this happens, the person who has them can masquerade as you until they expire. For this reason, you should destroy your Kerberos tickets when you are away from your computer.
Destroying your tickets is easy. Simply type kdestroy.
shell% kdestroy
shell%
If kdestroy fails to destroy your tickets, it will beep and give
an error message. For example, if kdestroy can't find any
tickets to destroy, it will give the following message:
shell% kdestroy
kdestroy: No credentials cache file found while destroying cache
shell%
Your password is the only way Kerberos has of verifying your identity. If someone finds out your password, that person can masquerade as you--send email that comes from you, read, edit, or delete your files, or log into other hosts as you--and no one will be able to tell the difference. For this reason, it is important that you choose a good password (see Password Advice), and keep it secret. If you need to give access to your account to someone else, you can do so through Kerberos. (See Granting Access to Your Account.) You should never tell your password to anyone, including your system administrator, for any reason. You should change your password frequently, particularly any time you think someone may have found out what it is.
To change your Kerberos password, use the kpasswd command. It
will ask you for your old password (to prevent someone else from walking
up to your computer when you're not there and changing your password),
and then prompt you for the new one twice. (The reason you have to type
it twice is to make sure you have typed it correctly.) For example,
user david would do the following:
shell% kpasswd
Password for david: <- Type your old password.
Enter new password: <- Type your new password.
Enter it again: <- Type the new password again.
Password changed.
shell%
If david typed the incorrect old password, he would get the following message:
shell% kpasswd
Password for david: <- Type the incorrect old password.
kpasswd: Password incorrect while getting initial ticket
shell%
If you make a mistake and don't type the new password the same way
twice, kpasswd will ask you to try again:
shell% kpasswd
Password for david: <- Type the old password.
Enter new password: <- Type the new password.
Enter it again: <- Type a different new password.
kpasswd: Password mismatch while reading password
shell%
Once you change your password, it takes some time for the change to propagate through the system. Depending on how your system is set up, this might be anywhere from a few minutes to an hour or more. If you need to get new Kerberos tickets shortly after changing your password, try the new password. If the new password doesn't work, try again using the old one.
Your password can include almost any character you can type (except control keys and the "enter" key). A good password is one you can remember, but that no one else can easily guess. Examples of bad passwords are words that can be found in a dictionary, any common or popular name, especially a famous person (or cartoon character), your name or username in any form (e.g., forward, backward, repeated twice, etc.), your spouse's, child's, or pet's name, your birth date, your social security number, and any sample password that appears in this (or any other) manual. MIT recommends that your password be at least 6 characters long, and contain UPPER- and lower-case letters, numbers, and/or punctuation marks. Some passwords that would be good if they weren't listed in this manual include:
Note: don't actually use any of the above passwords. They're
only meant to show you how to make up a good password. Passwords that
appear in a manual are the first ones intruders will try.
Kerberos V5 allows your system administrators to automatically
reject bad passwords, based on certain criteria, such as a password
dictionary or a minimum length. For example, if the user
jennifer, who had a policy "strict" that required a
minimum of 8 characaters, chose a password that was less than 8
characters, Kerberos would give an error message like the following:
shell% kpasswd
Password for jennifer: <- Type your old password here.
jennifer's password is controlled by the policy strict, which
requires a minimum of 8 characters from at least 3 classes (the five classes
are lowercase, uppercase, numbers, punctuation, and all other characters).
Enter new password: <- Type an insecure new password.
Enter it again: <- Type it again.
kpasswd: Password is too short while attempting to change password.
Please choose another password.
Enter new password: <- Type a good password here.
Enter it again: <- Type it again.
Password changed.
shell%
Your system administrators can choose the message that is displayed if you choose a bad password, so the message you see may be different from the above example.
If you need to give someone access to log into your account, you can do
so through Kerberos, without telling the person your password. Simply
create a file called .k5login in your home directory. This file
should contain the Kerberos principal (See What is a Kerberos Principal?.) of each person to whom you wish to give access. Each
principal must be on a separate line. Here is a sample .k5login
file:
jennifer@ATHENA.MIT.EDU
david@EXAMPLE.COM
This file would allow the users jennifer and
david to use your user ID, provided that they had
Kerberos tickets in their respective realms. If you will be logging
into other hosts across a network, you will want to include your own
Kerberos principal in your .k5login file on each of these hosts.
Using a .k5login file is much safer than giving out your
password, because:
.k5login file.
.k5login file is shared,
e.g., over NFS), that user does not inherit your network privileges.
One common application is to have a .k5login file in
root's home directory, giving root access to that machine to the
Kerberos principals listed. This allows system administrators to allow
users to become root locally, or to log in remotely as root,
without their having to give out the root password, and without anyone
having to type the root password over the network.
The Kerberos V5 applications are versions of existing UNIX network programs with the Kerberos features added.
The Kerberos V5 network programs are those programs that
connect to another host somewhere on the internet. These programs
include rlogin, telnet, ftp, rsh,
rcp, and ksu. These programs have all of the original
features of the corresponding non-Kerberos rlogin, telnet,
ftp, rsh, rcp, and su programs, plus
additional features that transparently use your Kerberos tickets for
negotiating authentication and optional encryption with the remote host.
In most cases, all you'll notice is that you no longer have to type your
password, because Kerberos has already proven your identity.
The Kerberos V5 network programs allow you the options of forwarding
your tickets to the remote host (if you obtained forwardable tickets
with the kinit program; see Obtaining Tickets with kinit), and
encrypting data transmitted between you and the remote host.
This section of the tutorial assumes you are familiar with the non-Kerberos versions of these programs, and highlights the Kerberos functions added in the Kerberos V5 package.
The Kerberos V5 telnet command works exactly like the
standard UNIX telnet program, with the following Kerberos options added:
telnet will assume
the same username unless you explicitly specify another.
For example, if david wanted to use the standard
UNIX telnet to connect to the machine
daffodil.mit.edu, he would type:
shell% telnet daffodil.example.com
Trying 128.0.0.5 ...
Connected to daffodil.example.com.
Escape character is '^]'.
NetBSD/i386 (daffodil) (ttyp3)
login: david
Password: <- david types his password here
Last login: Fri Jun 21 17:13:11 from trillium.mit.edu
Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994
The Regents of the University of California. All rights reserved.
NetBSD 1.1: Tue May 21 00:31:42 EDT 1996
Welcome to NetBSD!
shell%
Note that the machine
daffodil.example.com asked for
david's password. When he typed it, his password
was sent over the network unencrypted. If an intruder were watching
network traffic at the time, that intruder would know
david's password.
If, on the other hand, jennifer wanted to use the
Kerberos V5 telnet to connect to the machine
trillium.mit.edu, she could forward a
copy of her tickets, request an encrypted session, and log on as herself
as follows:
shell% telnet -a -f -x trillium.mit.edu
Trying 128.0.0.5...
Connected to trillium.mit.edu.
Escape character is '^]'.
[ Kerberos V5 accepts you as ``jennifer@mit.edu'' ]
[ Kerberos V5 accepted forwarded credentials ]
What you type is protected by encryption.
Last login: Tue Jul 30 18:47:44 from daffodil.example.com
Athena Server (sun4) Version 9.1.11 Tue Jul 30 14:40:08 EDT 2002
shell%
Note that jennifer's machine used Kerberos
to authenticate her to trillium.mit.edu,
and logged her in automatically as herself. She had an encrypted
session, a copy of her tickets already waiting for her, and she never
typed her password.
If you forwarded your Kerberos tickets, telnet automatically
destroys them when it exits. The full set of options to Kerberos V5
telnet are discussed in the Reference section of this manual.
(see telnet Reference)
The Kerberos V5 rlogin command works exactly like the
standard UNIX rlogin program, with the following Kerberos options added:
For example, if david wanted to use the standard
UNIX rlogin to connect to the machine
daffodil.example.com, he would type:
shell% rlogin daffodil.example.com -l david
Password: <- david types his password here
Last login: Fri Jun 21 10:36:32 from :0.0
Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994
The Regents of the University of California. All rights reserved.
NetBSD 1.1: Tue May 21 00:31:42 EDT 1996
Welcome to NetBSD!
shell%
Note that the machine
daffodil.example.com asked for
david's password. When he typed it, his password
was sent over the network unencrypted. If an intruder were watching
network traffic at the time, that intruder would know
david's password.
If, on the other hand, jennifer wanted to use
Kerberos V5 rlogin to connect to the machine
trillium.mit.edu, she could forward a
copy of her tickets, mark them as not forwardable from the remote host,
and request an encrypted session as follows:
shell% rlogin trillium.mit.edu -f -x
This rlogin session is using DES encryption for all data transmissions.
Last login: Thu Jun 20 16:20:50 from daffodil
Athena Server (sun4) Version 9.1.11 Tue Jul 30 14:40:08 EDT 2002
shell%
Note that jennifer's machine used Kerberos
to authenticate her to trillium.mit.edu,
and logged her in automatically as herself. She had an encrypted
session, a copy of her tickets were waiting for her, and she never typed
her password.
If you forwarded your Kerberos tickets, rlogin automatically
destroys them when it exits. The full set of options to Kerberos V5
rlogin are discussed in the Reference section of this manual.
(see rlogin Reference)
The Kerberos V5 FTP program works exactly like the standard
UNIX FTP program, with the following Kerberos features added:
ftp> prompt) sets the protection level. "Clear"
is no protection; "safe" ensures data integrity by verifying the
checksum, and "private" encrypts the data. Encryption also ensures
data integrity.
For example, suppose jennifer wants to get her
RMAIL file from the directory ~jennifer/Mail,
on the host daffodil.mit.edu. She wants
to encrypt the file transfer. The exchange would look like the
following:
shell% ftp daffodil.mit.edu
Connected to daffodil.mit.edu.
220 daffodil.mit.edu FTP server (Version 5.60) ready.
334 Using authentication type GSSAPI; ADAT must follow
GSSAPI accepted as authentication type
GSSAPI authentication succeeded
200 Data channel protection level set to private.
Name (daffodil.mit.edu:jennifer):
232 GSSAPI user jennifer@ATHENA.MIT.EDU is authorized as jennifer
230 User jennifer logged in.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> protect private
200 Protection level set to Private.
ftp> cd ~jennifer/MAIL
250 CWD command successful.
ftp> get RMAIL
227 Entering Passive Mode (128,0,0,5,16,49)
150 Opening BINARY mode data connection for RMAIL (361662 bytes).
226 Transfer complete.
361662 bytes received in 2.5 seconds (1.4e+02 Kbytes/s)
ftp> quit
shell%
The full set of options to Kerberos V5 FTP are discussed
in the Reference section of this manual. (see FTP Reference)
The Kerberos V5 rsh program works exactly like the standard
UNIX rlogin program, with the following Kerberos features added:
For example, if your Kerberos tickets allowed you to run programs on the
host
trillium@example.com as root, you could
run the date program as follows:
shell% rsh trillium.example.com -l root -x date
This rsh session is using DES encryption for all data transmissions.
Tue Jul 30 19:34:21 EDT 2002
shell%
If you forwarded your Kerberos tickets, rsh automatically
destroys them when it exits. The full set of options to Kerberos V5
rsh are discussed in the Reference section of this manual.
(see rsh Reference)
The Kerberos V5 rcp program works exactly like the standard
UNIX rcp program, with the following Kerberos features added:
For example, if you wanted to copy the file /etc/motd from the
host daffodil.mit.edu into the current
directory, via an encrypted connection, you would simply type:
shell% rcp -x daffodil.mit.edu:/etc/motd .
The rcp program negotiates authentication and encryption
transparently. The full set of options to Kerberos V5 rcp
are discussed in the Reference section of this manual. (see rcp Reference)
The Kerberos V5 ksu program replaces the standard UNIX su
program. ksu first authenticates you to Kerberos. Depending on
the configuration of your system, ksu may ask for your Kerberos
password if authentication fails. Note that you should never type
your password if you are remotely logged in using an unencrypted
connection.
Once ksu has authenticated you, if your Kerberos principal
appears in the target's .k5login file (see Granting Access to Your Account) or in the target's .k5users file (see below), it
switches your user ID to the target user ID.
For example, david has put
jennifer's Kerberos principal in his .k5login
file. If jennifer uses ksu to become
david, the exchange would look like this. (To
differentiate between the two shells, jennifer's
prompt is represented as jennifer% and
david's prompt is represented as
david%.)
jennifer% ksu david
Account david: authorization for jennifer@ATHENA.MIT.EDU successful
Changing uid to david (3382)
david%
Note that the new shell has a copy of jennifer's
tickets. The ticket filename contains david's UID
with .1 appended to it:
david% klist
Ticket cache: /tmp/krb5cc_3382.1
Default principal: jennifer@ATHENA.MIT.EDU
Valid starting Expires Service principal
07/31/04 21:53:01 08/01/04 07:52:53 krbtgt/ATHENA.MIT.EDU@ATHENA.MIT.EDU
07/31/04 21:53:39 08/01/04 07:52:53 host/daffodil.mit.edu@ATHENA.MIT.EDU
david%
If jennifer had not appeared in
david's .k5login file (and the system was
configured to ask for a password), the exchange would have looked like
this (assuming david has taken appropriate
precautions in protecting his password):
jennifer% ksu david
WARNING: Your password may be exposed if you enter it here and are logged
in remotely using an unsecure (non-encrypted) channel.
Kerberos password for david@ATHENA.MIT.EDU: <- jennifer types the wrong password here.
ksu: Password incorrect
Authentication failed.
jennifer%
Now, suppose david did not want to give
jennifer full access to his account, but wanted to
give her permission to list his files and use the "more" command to view
them. He could create a .k5users file giving her permission to
run only those specific commands.
The .k5users file is like the .k5login file, except that
each principal is optionally followed by a list of commands. ksu
will let those principals execute only the commands listed, using the
-e option. david's .k5users file
might look like the following:
jennifer@ATHENA.MIT.EDU /bin/ls /usr/bin/more
joeadmin@ATHENA.MIT.EDU /bin/ls
joeadmin/admin@ATHENA.MIT.EDU *
david@EXAMPLE.COM
The above .k5users file would let
jennifer run only the commands /bin/ls and
/usr/bin/more. It would let joeadmin run only
the command /bin/ls if he had regular tickets, but if he had
tickets for his admin instance,
joeadmin/admin@ATHENA.MIT.EDU, he would be able
to execute any command. The last line gives david
in the realm EXAMPLE.COM permission to execute any command.
(I.e., having only a Kerberos principal on a line is equivalent to
giving that principal permission to execute *.) This is so that
david can allow himself to execute commands when he logs
in, using Kerberos, from a machine in the realm EXAMPLE.COM.
Then, when jennifer wanted to list his home directory,
she would type:
jennifer% ksu david -e ls ~david
Authenticated jennifer@ATHENA.MIT.EDU
Account david: authorization for jennifer@ATHENA.MIT.EDU for execution of
/bin/ls successful
Changing uid to david (3382)
Mail News Personal misc bin
jennifer%
If jennifer had tried to give a different
command to ksu, it would have prompted for a password as with the
previous example.
Note that unless the .k5users file gives the target permission to
run any command, the user must use ksu with the -e
command option.
The ksu options you are most likely to use are:
ksu.
(e.g., the user joeadmin might want to use his
admin instance. See What is a Ticket?.)
ksu not to destroy your Kerberos tickets when ksu is
finished.
ksu needs to obtain tickets.
ksu needs to obtain tickets.
ksu to copy your Kerberos tickets only if the UID you are
switching is the same as the Kerberos primary (either yours or the one
specified by the -n option).
ksu not to copy any Kerberos tickets to the new UID.
ksu to execute command and then exit. See the
description of the .k5users file above.
ksu to pass everything
after -a to the target shell.
The full set of options to Kerberos V5 ksu are discussed
in the Reference section of this manual. (see ksu Reference)
This section will include copies of the manual pages for the
Kerberos V5 client programs. You can read the manual entry for any
command by typing man command, where command is the name
of the command for which you want to read the manual entry. For
example, to read the kinit manual entry, you would type:
shell% man kinit
Note: To be able to view the Kerberos V5 manual pages on line, you
may need to add the directory /usr/local/man to your MANPATH
environment variable. (Remember to replace /usr/local with
the top-level directory in which Kerberos V5 is installed.) For
example, if you had the the following line in your .login
file2:
setenv MANPATH /usr/local/man:/usr/man
and the Kerberos V5 man pages were in the directory
/usr/krb5/man, you would change the line to the following:
setenv MANPATH /usr/krb5/man:/usr/local/man:/usr/man
The typical format of a typical Kerberos principal is
primary/instance@REALM.
telnet and
rsh), "ftp" (FTP), "krbtgt" (authentication;
cf. ticket-granting ticket), and "pop" (email).
Note: the realm
EXAMPLE.COM must be listed in your computer's Kerberos
configuration file, /etc/krb5.conf.
The MANPATH variable may be specified in a different
initialization file, depending on your operating system. Some of the
files in which you might specify environment variables include
.login, .profile, or .cshrc.