481 lines
15 KiB
Plaintext
481 lines
15 KiB
Plaintext
<!-- $Id: kerberos.sgml,v 1.4 1995/07/10 20:14:08 markm Exp $ -->
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<!-- The FreeBSD Documentation Project -->
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<sect><heading>Kerberos<label id="kerberos"></heading>
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<p><em>Contributed by &a.mark; (based on contribution by &a.md;).</em>
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Kerberos is a network add-on system/protocol that allows users to
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authenticate themselves through the services of a secure server.
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Services such as remote login, remote copy, secure inter-system
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file copying and other high-risk tasks are made considerably safer
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and more controllable.
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The following instructions can be used as a guide on how to
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set up Kerberos as distributed for FreeBSD. However, you should refer
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to the relevant manual pages for a complete description.
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In FreeBSD, the Kerberos is not that from the original 4.4 BSD,
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distribution, but eBones, which had been previously ported to
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FreeBSD 1.1.5.1, and was sourced from outside the USA/Canada,
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and is thus available to system owners outside those countries.
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For those needing to get a legal foreign distribution of this
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software, please <em>DO NOT</em> get it from a USA or Canada site.
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You will get that site in <em>big</em> trouble! A legal copy of this is
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available from <tt>skeleton.mikom.csir.co.za</tt>, which is in South
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Africa.
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<sect1>
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<heading>Creating the initial database</heading>
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<p>This is done on the Kerberos server only. First make sure that your
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don't have any old Kerberos databases around. You should change to the
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directory <tt>/etc/kerberosIV</tt> and check that only the following
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files are present:
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<tscreen><verb>
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grunt# cd /etc/kerberosIV
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grunt# ls
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README krb.conf krb.realms
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</verb></tscreen>
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<p>If any additional files (such as <tt>principal.*</tt> or
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<tt>master_key</tt>) exist, then use the <tt>kdb_destroy</tt>
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command to destroy the old Kerberos database, of if Kerberos
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is not running, simply delete the extra files with <tt>rm</tt>.
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You should now edit the <tt>krb.conf</tt> and <tt>krb.realms</tt>
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files to define your Kerberos realm. In this case the realm will
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be <it>GRONDAR.ZA</it> and the server is <it>grunt.grondar.za</it>.
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We edit or create the <tt>krb.conf</tt> file:
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<tscreen><verb>
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grunt# cat krb.conf
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GRONDAR.ZA
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GRONDAR.ZA grunt.grondar.za admin server
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CS.BERKELEY.EDU okeeffe.berkeley.edu
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ATHENA.MIT.EDU kerberos.mit.edu
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ATHENA.MIT.EDU kerberos-1.mit.edu
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ATHENA.MIT.EDU kerberos-2.mit.edu
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ATHENA.MIT.EDU kerberos-3.mit.edu
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LCS.MIT.EDU kerberos.lcs.mit.edu
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TELECOM.MIT.EDU bitsy.mit.edu
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ARC.NASA.GOV trident.arc.nasa.gov
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</verb></tscreen>
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<p>In this case, the other realms do not need to be there.
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They are here as an example of how a machine may be made aware
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of multiple realms. You may wish to not include them for simplicity.
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The first line names the realm in which this system works. The other
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lines contain realm/host entries. The first item on a line is a realm,
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and the second is a host in that realm that is acting as a ``key
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distribution centre''. The words ``admin server'' following a hosts
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name means that host also provides an administrative database server.
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For further explanation of these terms, please consult the Kerberos
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man pages.
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Now we have to add <it>grunt.grondar.za</it> to the <it>GRONDAR.ZA</it>
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realm and also add an entry to put all hosts in the <it>.grondar.za</it>
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domain in the <it>GRONDAR.ZA</it> realm. The <tt>krb.realms</tt> file
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would be updated as follows:
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<tscreen><verb>
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grunt# cat krb.realms
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grunt.grondar.za GRONDAR.ZA
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.grondar.za GRONDAR.ZA
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.berkeley.edu CS.BERKELEY.EDU
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.MIT.EDU ATHENA.MIT.EDU
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.mit.edu ATHENA.MIT.EDU
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</verb></tscreen>
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<p>Again, the other realms do not need to be there.
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They are here as an example of how a machine may be made aware
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of multiple realms. You may wish to remove them to simplify things.
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The first line puts the <it>specific</it> system into the named
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realm. The rest of the lines show how to default systems of a
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particular subdomain to a named realm.
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Now we're ready to create the database. This only needs to run on
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the Kerberos server (or Key Distribution Centre). Issue the
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<tt>kdb_init</tt> command to do this:
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<tscreen><verb>
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grunt# kdb_init
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Realm name [default ATHENA.MIT.EDU ]: GRONDAR.ZA
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You will be prompted for the database Master Password.
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It is important that you NOT FORGET this password.
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Enter Kerberos master key:
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</verb></tscreen>
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<p>Now we have to save the key so that servers on the local
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machine can pick it up. Use the <tt>kstash</tt> command to
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do this.
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<tscreen><verb>
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grunt# kstash
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Enter Kerberos master key:
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Current Kerberos master key version is 1.
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Master key entered. BEWARE!
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</verb></tscreen>
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<p>This saves the encrypted master password in
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<tt>/etc/kerberosIV/master_key</tt>.
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<sect1>
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<heading>Making it all run</heading>
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<p>Two principals need to be added to the database for <it>each</it>
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system that will be secured with Kerberos. Their names are
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<tt>kpasswd</tt> and <tt>rcmd</tt> These two principals are
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made for each system, with the instance being the name of the
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individual system.
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These daemons, <tt>kpasswd</tt> and <tt>rcmd</tt> allow other systems
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to change Kerberos passwords and run commands like <tt>rcp</tt>,
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<tt>rlogin</tt> and <tt>rsh</tt>.
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Now lets add these entries:
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<tscreen><verb>
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grunt# kdb_edit
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Opening database...
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Enter Kerberos master key:
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Current Kerberos master key version is 1.
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Master key entered. BEWARE!
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Previous or default values are in [brackets] ,
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enter return to leave the same, or new value.
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Principal name: passwd
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Instance: grunt
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<Not found>, Create [y] ? y
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Principal: passwd, Instance: grunt, kdc_key_ver: 1
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New Password: <---- enter RANDOM here
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Verifying password
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New Password: <---- enter RANDOM here
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Random password [y] ? y
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Principal's new key version = 1
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Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ?
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Max ticket lifetime (*5 minutes) [ 255 ] ?
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Attributes [ 0 ] ?
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Edit O.K.
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Principal name: rcmd
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Instance: grunt
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<Not found>, Create [y] ?
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Principal: rcmd, Instance: grunt, kdc_key_ver: 1
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New Password: <---- enter RANDOM here
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Verifying password
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New Password: <---- enter RANDOM here
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Random password [y] ?
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Principal's new key version = 1
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Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ?
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Max ticket lifetime (*5 minutes) [ 255 ] ?
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Attributes [ 0 ] ?
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Edit O.K.
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Principal name: <---- null entry here will cause an exit
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</verb></tscreen>
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<sect1>
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<heading>Creating the server file</heading>
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<p>We now have to extract all the instances which define the services
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on each machine. For this we use the <tt>ext_srvtab</tt> command.
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This will create a file which must be copied or moved <it>by secure
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means</it> to each Kerberos client's /etc/kerberosIV directory. This
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file must be present on each server and client, and is crucial to the
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operation of Kerberos.
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<tscreen><verb>
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grunt# ext_srvtab grunt
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Enter Kerberos master key:
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Current Kerberos master key version is 1.
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Master key entered. BEWARE!
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Generating 'grunt-new-srvtab'....
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</verb></tscreen>
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<p>Now, this command only generates a temporary file
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which must be renamed to <tt>srvtab</tt> so that all the
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server can pick it up. Use the <tt>mv</tt> command to move it
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into place on the original system:
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<tscreen><verb>
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grunt# mv grunt-new-srvtab srvtab
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</verb></tscreen>
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<p>If the file is for a client system, and the network is not
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deemed safe, then copy the <tt><client>-new-srvtab</tt> to
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removable media and transport it by secure physical means. Be
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sure to rename it to <tt>srvtab</tt> in the client's
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<tt>/etc/kerberosIV</tt> directory, and make sure it is mode 600:
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<tscreen><verb>
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grumble# mv grumble-new-srvtab srvtab
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grumble# chmod 600 srvtab
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</verb></tscreen>
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<sect1>
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<heading>Populating the database</heading>
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<p>We now have to add some user entries into the database.
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First lets create an entry for the user <it>jane</it>. Use
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the <tt>kdb_edit</tt> command to do this:
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<tscreen><verb>
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grunt# kdb_edit
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Opening database...
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Enter Kerberos master key:
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Current Kerberos master key version is 1.
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Master key entered. BEWARE!
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Previous or default values are in [brackets] ,
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enter return to leave the same, or new value.
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Principal name: jane
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Instance:
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<Not found>, Create [y] ? y
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Principal: jane, Instance: , kdc_key_ver: 1
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New Password: <---- enter a secure password here
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Verifying password
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New Password: <---- re-enter the password here
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Principal's new key version = 1
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Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ?
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Max ticket lifetime (*5 minutes) [ 255 ] ?
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Attributes [ 0 ] ?
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Edit O.K.
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Principal name: <---- null entry here will cause an exit
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</verb></tscreen>
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<sect1>
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<heading>Testing it all out</heading>
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<p>First we have to start the Kerberos daemons. NOTE that if you have
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correctly edited your <tt>/etc/sysconfig</tt> then this will happen
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automatically when you reboot. This is only necessary on the Kerberos
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server. Kerberos clients will automagically get what they need from
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the <tt>/etc/kerberosIV</tt> directory.
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<tscreen><verb>
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grunt# kerberos &
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grunt# Kerberos server starting
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Sleep forever on error
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Log file is /var/log/kerberos.log
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Current Kerberos master key version is 1.
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Master key entered. BEWARE!
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Current Kerberos master key version is 1
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Local realm: GRONDAR.ZA
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grunt# kadmind -n &
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grunt# KADM Server KADM0.0A initializing
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Please do not use 'kill -9' to kill this job, use a
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regular kill instead
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Current Kerberos master key version is 1.
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Master key entered. BEWARE!
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</verb></tscreen>
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<p>Now we can try using the <tt>kinit</tt> command to get a ticket for
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the id <it>jane</it> that we created above:
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<tscreen><verb>
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grunt$ kinit jane
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MIT Project Athena (grunt.grondar.za)
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Kerberos Initialization for "jane"
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Password:
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</verb></tscreen>
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<p>Try listing the tokens using <tt>klist</tt> to see if we really have them:
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<tscreen><verb>
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grunt$ klist
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Ticket file: /tmp/tkt245
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Principal: jane@GRONDAR.ZA
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Issued Expires Principal
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Apr 30 11:23:22 Apr 30 19:23:22 krbtgt.GRONDAR.ZA@GRONDAR.ZA
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</verb></tscreen>
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<p>Now try changing the password using <tt>passwd</tt> to check if the
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kpasswd daemon can get authorization to the Kerberos database:
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<tscreen><verb>
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grunt$ passwd
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realm GRONDAR.ZA
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Old password for jane:
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New Password for jane:
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Verifying password
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New Password for jane:
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Password changed.
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</verb></tscreen>
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<sect1>
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<heading>Adding <tt>su</tt> privileges</heading>
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<p>Kerberos allows us to give <it>each</it> user who needs root
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privileges their own <it>separate</it> <tt>su</tt>password. We
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could now add an id which is authorized to <tt>su</tt> to <it>root</it>.
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This is controlled by having an instance of <it>root</it> associated
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with a principal. Using <tt>kdb_edit</tt> we can create the entry
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<it>jane.root</it> in the Kerberos database:
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<tscreen><verb>
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grunt# kdb_edit
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Opening database...
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Enter Kerberos master key:
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Current Kerberos master key version is 1.
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Master key entered. BEWARE!
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Previous or default values are in [brackets] ,
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enter return to leave the same, or new value.
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Principal name: jane
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Instance: root
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<Not found>, Create [y] ? y
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Principal: jane, Instance: root, kdc_key_ver: 1
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New Password: <---- enter a SECURE password here
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Verifying password
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New Password: <---- re-enter the password here
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Principal's new key version = 1
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Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ?
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Max ticket lifetime (*5 minutes) [ 255 ] ? 12 <--- Keep this short!
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Attributes [ 0 ] ?
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Edit O.K.
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Principal name: <---- null entry here will cause an exit
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</verb></tscreen>
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<p>Now try getting tokens for it to make sure it works:
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<tscreen><verb>
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grunt# kinit jane.root
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MIT Project Athena (grunt.grondar.za)
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Kerberos Initialization for "jane.root"
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Password:
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</verb></tscreen>
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<p>Now we need to add the user to root's <tt>.klogin</tt> file:
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<tscreen><verb>
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grunt# cat /root/.klogin
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jane.root@GRONDAR.ZA
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</verb></tscreen>
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<p>Now try doing the <tt>su</tt>:
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<tscreen><verb>
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[jane@grunt 10407] su
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Password:
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grunt#
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</verb></tscreen>
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and take a look at what tokens we have:
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<tscreen><verb>
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grunt# klist
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Ticket file: /tmp/tkt_root_245
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Principal: jane.root@GRONDAR.ZA
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Issued Expires Principal
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May 2 20:43:12 May 3 04:43:12 krbtgt.GRONDAR.ZA@GRONDAR.ZA
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</verb></tscreen>
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<sect1>
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<heading>Using other commands</heading>
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<p>In an earlier example, we created a principal called <tt>jane</tt>
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with an instance <tt>root</tt>. This was based on a user with the
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same name as the principal, and this is a Kerberos default; that a
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<em><principal>.<instance></em> of the form
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<em><username>.</em><tt>root</tt> will allow that
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<em><username></em> to <tt>su</tt> to root if the necessary
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entries are in the <tt>.klogin</tt> file in <tt>root</tt>'s home
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directory:
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<tscreen><verb>
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grunt# cat /root/.klogin
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jane.root@GRONDAR.ZA
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</verb></tscreen>
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<p>Likewise, if a user has in their own home directory lines of the
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form:
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<tscreen><verb>
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[jane@grunt 10543] cat ~/.klogin
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jane@GRONDAR.ZA
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jack@GRONDAR.ZA
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</verb></tscreen>
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<p>This allows anyone in the <em>GRONDAR.ZA</em> realm who has
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authenticated themselves to <em>jane</em> or <em>jack</em> (via
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<tt>kinit</tt>, see above) access to <tt>rlogin</tt> to <em>jane</em>'s
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account or files on this system (<em>grunt</em>) via <tt>rlogin</tt>,
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<tt>rsh</tt> or <tt>rcp</tt>.
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For example, Jane now logs into another system, using Kerberos:
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<tscreen><verb>
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[jane@grumble 573] kinit
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MIT Project Athena (grunt.grondar.za)
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Password:
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[jane@grumble 574] rlogin grunt
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Last login: Mon May 1 21:14:47 from grumble
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Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994
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The Regents of the University of California. All rights reserved.
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FreeBSD BUILT-19950429 (GR386) #0: Sat Apr 29 17:50:09 SAT 1995
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[jane@grunt 10567]
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</verb></tscreen>
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<p>Or Jack logs into Jane's account on the same machine (Jane having set up
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the <tt>.klogin</tt> file as above, and the person in charge of Kerberos
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having set up principal <em>jack</em> with a null instance:
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<tscreen><verb>
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[jack@grumble 573] kinit
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[jack@grumble 574] rlogin grunt -l jane
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MIT Project Athena (grunt.grondar.za)
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Password:
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Last login: Mon May 1 21:16:55 from grumble
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Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994
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The Regents of the University of California. All rights reserved.
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FreeBSD BUILT-19950429 (GR386) #0: Sat Apr 29 17:50:09 SAT 1995
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[jane@grunt 10578]
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</verb></tscreen>
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