Kerberos Software Installation

Many UNIX systems already have kerberos installed. Use "which kinit" to see whether this software is already in your path. If not, check if /usr/krb5 or /usr/kerberos directories exist on your workstation - if so, add /usr/kerberos/bin (or the equivalent for krb5) to the front of your path.

On RedHat Linux systems, you will need to install the following RPM's (versions will vary):

• krb5-libs
• krb5-workstation
• pam_krb5

You may also download kerberos software from Fermilab. "Lite" versions of Linux and Windows clients have been made available. You can download the software here. After untarring the Linux version, or unzipping the Windows version, follow the instructions which accompany the software.

If you have an older version of Linux, you can download a statically-linked version of the kerberos clients here. You will also need the krb5.conf file. Please click here for more details on installing and using this software.

If kerberos software is already installed on your system, you will need to modify the configuration file so that your machine knows how to contact the Fermilab key servers. If you will only access Fermilab via kerberos, install krb5.conf in /etc. If you are already using kerberos to access another site, for example, NCSA, you will need to modify your existing /etc/krb5.conf file as follows:

• In the [realms] section, add

           FNAL.GOV = {
   	  kdc = krb-fnal-1.fnal.gov:88
  	  kdc = krb-fnal-2.fnal.gov:88
  	  kdc = krb-fnal-3.fnal.gov:88
  	  kdc = krb-fnal-4.fnal.gov:88
  	  kdc = krb-fnal-5.fnal.gov:88
  	  kdc = krb-fnal-6.fnal.gov:88
  	  admin_server = krb-fnal-admin.fnal.gov
  	  master_kdc = krb-fnal-admin.fnal.gov:88
  	  default_domain = fnal.gov
  
  	 WIN.FNAL.GOV = {
  	  kdc = littlebird.win.fnal.gov:88
  	  kdc = bigbird.win.fnal.gov:88
  	  default_domain = fnal.gov
  	  }
          }

• In a [domain_realm] section, add

          .fnal.gov       = FNAL.GOV
  	.dhcp.fnal.gov  = FNAL.GOV	
  

SSH with Kerberos Support

The SSH that is distributed as a part of the Fermi Linux Distributions contains the Kerberos-enabled SSH needed to connect to the Fermilab LQCD cluster head nodes.

If you are using a distribution of Linux which doesn't include Kerberos-enabled SSH, please download one of the following versions of SSH and use that SSH to connect to the LQCD Cluster head nodes:

• ssh.rhes4: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), stripped
• ssh_sl5: ELF 64-bit LSB shared object, AMD x86-64, version 1 (SYSV), not stripped

If you still unable to install a SSH client for your distribution of Linux, please email us at lqcd-admin@fnal.gov.

User Authentication using Kerberos

Here is a sample session showing a typical kerberos dialog. djholm@FNAL.GOV is the kerberos principal. "which rlogin" is used to verify that the kerberized version of rlogin is used (the non-kerberized version will be rejected).

dalrott:~$ kinit -r 7d djholm@FNAL.GOV
Password for djholm@FNAL.GOV:

dalrott:~$ which rlogin
/usr/krb5/bin/rlogin

dalrott:~$ rlogin lqcd.fnal.gov
This rlogin session is using DES encryption for all data transmissions.

Scientific Linux Fermi LTS release 4.4 (Wilson)
.
.
.
lqcd:~$ 

Kerberos Authentication Usage Notes

• You should only kinit on your local machine, from its console. Don't use kinit over a network connection, since this can expose your kerberos password.
• You will probably want to request renewable tickets, since tickets expire 24 hours after they are issued/renewed if they are not renewed with "kinit -R". Tickets can be renewed for up to 7 days if you use "kinit -r 7d". The maximum renewable period is 7 days.
• Use klist to check whether you hold a valid ticket. For example:

  dalrott:/slack/djholm$ klist
  Ticket cache: /tmp/krb5cc_tty1
  Default principal: djholm@FNAL.GOV
  
  Valid starting     Expires            Service principal
  05/15/07 15:57:37  05/16/07 17:57:37  krbtgt/FNAL.GOV@FNAL.GOV
  

If you are connecting from home via a firewall which uses NAT (network address translation), you'll need to use addressless tickets. The Fermilab version of kerberos will give you addressless tickets if you use the "-n" switch. Other versions of kerberos may use the "-A" switch. Check your man page for kinit or use "kinit --help" to see which switch is supported. With addressless tickets, unfortunately rsh/rcp/rlogin will not work when traversing a NAT. However, telnet and ssh/scp do work. The Fermilab lite version of kerberos for Windows supports addressless tickets. The lite version for Linux currently does not. An unofficial cut of the Linux lite version (use at your own risk) which does support the "-n" switch is available here.

User Authentication using Cryptocard

Cryptocards generate passwords which are only valid for a single use. If kerberos client software isn't available, using a cryptocard is the only other means of accessing Fermilab systems. These cards look like a calculator:

Two styles of cryptocard have been issued by Fermilab, and unfortunately their usage is different. The Computing Division has a good chapter in their kerberos documentation which explains how to use both types of cards.

Here's a typical session with a cryptocard:

dalrott:~$ ssh lqcd.fnal.gov

login: djholm
Press ENTER and compare this challenge to the one on your display: [00160613]
Enter the displayed response: a37ddb18

Scientific Linux Fermi LTS release 4.4 (Wilson)

                              NOTICE TO USERS

...

lqcd:~$ 

In this example, the ssh server on lqcd issued a cryptocard challenge. After turning on an old-style cryptocard and entering a valid pin, Fermilab is displayed. Hitting ENT displays a number which (almost always) matches the challenge. Hitting ENT again displays the response which must be typed at workstation. With the new-style cryptocards, the challenge is not displayed, only the response. For detailed instructions, see this link.

Cryptocard Authentication Notes

• When you use ssh to login to lqcd just hit enter if you get the password prompt - do not type in a password. This will cause a cryptocard challenge. If you type in a password, you will get a "Permission denied, please try again" error, followed by another password prompt. Only a blank password will result in a cryptocard challenge.
• The advantage of using ssh is that X-window forwarding will allow you to open windows from lqcd.fnal.gov on your workstation. However, when your ticket expires this stops working. If you remember to renew your ticket before expiration with "kinit -R", the X forwarding will continue to work.