ae77177087
several new kerberos related libraries and applications to FreeBSD:
o kgetcred(1) allows one to manually get a ticket for a particular service.
o kf(1) securily forwards ticket to another host through an authenticated
and encrypted stream.
o kcc(1) is an umbrella program around klist(1), kswitch(1), kgetcred(1)
and other user kerberos operations. klist and kswitch are just symlinks
to kcc(1) now.
o kswitch(1) allows you to easily switch between kerberos credentials if
you're running KCM.
o hxtool(1) is a certificate management tool to use with PKINIT.
o string2key(1) maps a password into key.
o kdigest(8) is a userland tool to access the KDC's digest interface.
o kimpersonate(8) creates a "fake" ticket for a service.
We also now install manpages for some lirbaries that were not installed
before, libheimntlm and libhx509.
- The new HEIMDAL version no longer supports Kerberos 4. All users are
recommended to switch to Kerberos 5.
- Weak ciphers are now disabled by default. To enable DES support (used
by telnet(8)), use "allow_weak_crypto" option in krb5.conf.
- libtelnet, pam_ksu and pam_krb5 are now compiled with error on warnings
disabled due to the function they use (krb5_get_err_text(3)) being
deprecated. I plan to work on this next.
- Heimdal's KDC now require sqlite to operate. We use the bundled version
and install it as libheimsqlite. If some other FreeBSD components will
require it in the future we can rename it to libbsdsqlite and use for these
components as well.
- This is not a latest Heimdal version, the new one was released while I was
working on the update. I will update it to 1.5.2 soon, as it fixes some
important bugs and security issues.
1710 lines
59 KiB
Plaintext
1710 lines
59 KiB
Plaintext
@c $Id$
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@node Setting up a realm, Applications, Building and Installing, Top
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@chapter Setting up a realm
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A
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@cindex realm
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realm is an administrative domain. The name of a Kerberos realm is
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usually the Internet domain name in uppercase. Call your realm the same
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as your Internet domain name if you do not have strong reasons for not
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doing so. It will make life easier for you and everyone else.
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@menu
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* Configuration file::
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* Creating the database::
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* Modifying the database::
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* Checking the setup::
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* keytabs::
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* Serving Kerberos 4/524/kaserver::
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* Remote administration::
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* Password changing::
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* Testing clients and servers::
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* Slave Servers::
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* Incremental propagation::
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* Encryption types and salting::
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* Credential cache server - KCM::
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* Cross realm::
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* Transit policy::
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* Setting up DNS::
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* Using LDAP to store the database::
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* Providing Kerberos credentials to servers and programs::
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* Setting up PK-INIT::
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* Debugging Kerberos problems::
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@end menu
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@node Configuration file, Creating the database, Setting up a realm, Setting up a realm
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@section Configuration file
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To setup a realm you will first have to create a configuration file:
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@file{/etc/krb5.conf}. The @file{krb5.conf} file can contain many
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configuration options, some of which are described here.
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There is a sample @file{krb5.conf} supplied with the distribution.
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The configuration file is a hierarchical structure consisting of
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sections, each containing a list of bindings (either variable
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assignments or subsections). A section starts with
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@samp{[@samp{section-name}]}. A binding consists of a left hand side, an equal sign
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(@samp{=}) and a right hand side (the left hand side tag must be
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separated from the equal sign with some whitespace). Subsections have a
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@samp{@{} as the first non-whitespace character after the equal sign. All
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other bindings are treated as variable assignments. The value of a
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variable extends to the end of the line.
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@example
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[section1]
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a-subsection = @{
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var = value1
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other-var = value with @{@}
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sub-sub-section = @{
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var = 123
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@}
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@}
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var = some other value
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[section2]
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var = yet another value
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@end example
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In this manual, names of sections and bindings will be given as strings
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separated by slashes (@samp{/}). The @samp{other-var} variable will thus
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be @samp{section1/a-subsection/other-var}.
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For in-depth information about the contents of the configuration file, refer to
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the @file{krb5.conf} manual page. Some of the more important sections
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are briefly described here.
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The @samp{libdefaults} section contains a list of library configuration
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parameters, such as the default realm and the timeout for KDC
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responses. The @samp{realms} section contains information about specific
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realms, such as where they hide their KDC@. This section serves the same
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purpose as the Kerberos 4 @file{krb.conf} file, but can contain more
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information. Finally the @samp{domain_realm} section contains a list of
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mappings from domains to realms, equivalent to the Kerberos 4
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@file{krb.realms} file.
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To continue with the realm setup, you will have to create a configuration file,
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with contents similar to the following.
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@example
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[libdefaults]
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default_realm = MY.REALM
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[realms]
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MY.REALM = @{
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kdc = my.kdc my.slave.kdc
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kdc = my.third.kdc
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kdc = 130.237.237.17
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kdc = [2001:6b0:1:ea::100]:88
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@}
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[domain_realm]
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.my.domain = MY.REALM
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@end example
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If you use a realm name equal to your domain name, you can omit the
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@samp{libdefaults}, and @samp{domain_realm}, sections. If you have a DNS
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SRV-record for your realm, or your Kerberos server has DNS CNAME
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@samp{kerberos.my.realm}, you can omit the @samp{realms} section too.
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@cindex KRB5_CONFIG
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If you want to use a different configuration file then the default you
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can point a file with the enviroment variable @samp{KRB5_CONFIG}.
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@example
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env KRB5_CONFIG=$HOME/etc/krb5.conf kinit user@@REALM
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@end example
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@node Creating the database, Modifying the database, Configuration file, Setting up a realm
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@section Creating the database
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The database library will look for the database in the directory
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@file{@value{dbdir}}, so you should probably create that directory.
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Make sure the directory has restrictive permissions.
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@example
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# mkdir /var/heimdal
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@end example
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The keys of all the principals are stored in the database. If you
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choose to, these can be encrypted with a master key. You do not have to
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remember this key (or password), but just to enter it once and it will
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be stored in a file (@file{/var/heimdal/m-key}). If you want to have a
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master key, run @samp{kstash} to create this master key:
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@example
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# kstash
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Master key:
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Verifying password - Master key:
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@end example
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If you want to generate a random master key you can use the
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@kbd{--random-key} flag to kstash. This will make sure you have a good key
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on which attackers can't do a dictionary attack.
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If you have a master key, make sure you make a backup of your master
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key file; without it backups of the database are of no use.
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To initialise the database use the @command{kadmin} program, with the
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@kbd{-l} option (to enable local database mode). First issue a
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@kbd{init MY.REALM} command. This will create the database and insert
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default principals for that realm. You can have more than one realm in
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one database, so @samp{init} does not destroy any old database.
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Before creating the database, @samp{init} will ask you some questions
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about maximum ticket lifetimes.
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After creating the database you should probably add yourself to it. You
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do this with the @samp{add} command. It takes as argument the name of a
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principal. The principal should contain a realm, so if you haven't set up
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a default realm, you will need to explicitly include the realm.
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@example
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# kadmin -l
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kadmin> init MY.REALM
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Realm max ticket life [unlimited]:
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Realm max renewable ticket life [unlimited]:
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kadmin> add me
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Max ticket life [unlimited]:
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Max renewable life [unlimited]:
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Attributes []:
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Password:
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Verifying password - Password:
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@end example
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Now start the KDC and try getting a ticket.
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@example
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# kdc &
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# kinit me
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me@@MY.REALMS's Password:
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# klist
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Credentials cache: /tmp/krb5cc_0
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Principal: me@@MY.REALM
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Issued Expires Principal
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Aug 25 07:25:55 Aug 25 17:25:55 krbtgt/MY.REALM@@MY.REALM
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@end example
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If you are curious you can use the @samp{dump} command to list all the
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entries in the database. It should look something similar to the
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following example (note that the entries here are truncated for
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typographical reasons):
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@smallexample
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kadmin> dump
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me@@MY.REALM 1:0:1:0b01d3cb7c293b57:-:0:7:8aec316b9d1629e3baf8 ...
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kadmin/admin@@MY.REALM 1:0:1:e5c8a2675b37a443:-:0:7:cb913ebf85 ...
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krbtgt/MY.REALM@@MY.REALM 1:0:1:52b53b61c875ce16:-:0:7:c8943be ...
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kadmin/changepw@@MY.REALM 1:0:1:f48c8af2b340e9fb:-:0:7:e3e6088 ...
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@end smallexample
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@node Modifying the database, Checking the setup, Creating the database, Setting up a realm
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@section Modifying the database
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All modifications of principals are done with with kadmin.
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A principal has several attributes and lifetimes associated with it.
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Principals are added, renamed, modified, and deleted with the kadmin
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commands @samp{add}, @samp{rename}, @samp{modify}, @samp{delete}.
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Both interactive editing and command line flags can be used (use --help
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to list the available options).
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There are different kinds of types for the fields in the database;
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attributes, absolute time times and relative times.
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@subsection Attributes
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When doing interactive editing, attributes are listed with @samp{?}.
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The attributes are given in a comma (@samp{,}) separated list.
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Attributes are removed from the list by prefixing them with @samp{-}.
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@smallexample
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kadmin> modify me
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Max ticket life [1 day]:
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Max renewable life [1 week]:
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Principal expiration time [never]:
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Password expiration time [never]:
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Attributes [disallow-renewable]: requires-pre-auth,-disallow-renewable
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kadmin> get me
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Principal: me@@MY.REALM
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[...]
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Attributes: requires-pre-auth
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@end smallexample
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@subsection Absolute times
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The format for absolute times are any of the following:
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@smallexample
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never
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now
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YYYY-mm-dd
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YYYY-mm-dd HH:MM:SS
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@end smallexample
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@subsection Relative times
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The format for relative times are any of the following combined:
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@smallexample
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N year
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M month
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O day
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P hour
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Q minute
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R second
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@end smallexample
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@c Describe more of kadmin commands here...
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@node Checking the setup, keytabs, Modifying the database, Setting up a realm
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@section Checking the setup
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There are two tools that can check the consistency of the Kerberos
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configuration file and the Kerberos database.
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The Kerberos configuration file is checked using
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@command{verify_krb5_conf}. The tool checks for common errors, but
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commonly there are several uncommon configuration entries that are
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never added to the tool and thus generates ``unknown entry'' warnings.
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This is usually nothing to worry about.
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The database check is built into the kadmin tool. It will check for
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common configuration error that will cause problems later. Common
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check are for existence and flags on important principals. The
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database check by run by the following command :
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@example
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kadmin -l check REALM.EXAMPLE.ORG
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@end example
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@node keytabs, Serving Kerberos 4/524/kaserver, Checking the setup, Setting up a realm
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@section keytabs
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To extract a service ticket from the database and put it in a keytab, you
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need to first create the principal in the database with @samp{add}
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(using the @kbd{--random-key} flag to get a random key) and then
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extract it with @samp{ext_keytab}.
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@example
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kadmin> add --random-key host/my.host.name
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Max ticket life [unlimited]:
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Max renewable life [unlimited]:
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Attributes []:
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kadmin> ext host/my.host.name
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kadmin> exit
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# ktutil list
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Version Type Principal
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1 des-cbc-md5 host/my.host.name@@MY.REALM
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1 des-cbc-md4 host/my.host.name@@MY.REALM
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1 des-cbc-crc host/my.host.name@@MY.REALM
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1 des3-cbc-sha1 host/my.host.name@@MY.REALM
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@end example
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@node Serving Kerberos 4/524/kaserver, Remote administration, keytabs, Setting up a realm
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@section Serving Kerberos 4/524/kaserver
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Heimdal can be configured to support 524, Kerberos 4 or kaserver. All
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these services are turned off by default. Kerberos 4 is always
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supported by the KDC, but the Kerberos 4 client support also depends
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on Kerberos 4 support having been included at compile-time, using
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@kbd{--with-krb4=dir}.
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@subsection 524
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524 is a service that allows the KDC to convert Kerberos 5 tickets to
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Kerberos 4 tickets for backward compatibility. See also Using 2b
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tokens with AFS in @xref{AFS}.
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524 can be turned on by adding this to the configuration file
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@example
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[kdc]
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enable-524 = yes
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@end example
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@subsection Kerberos 4
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Kerberos 4 is the predecessor to to Kerberos 5. It only supports
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single DES@. You should only enable Kerberos 4 support if you have
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needs for compatibility with an installed base of Kerberos 4
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clients/servers.
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Kerberos 4 can be turned on by adding this to the configuration file
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@example
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[kdc]
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enable-kerberos4 = yes
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@end example
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@subsection kaserver
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Kaserver is a Kerberos 4 that is used in AFS@. The protocol has some
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extra features over plain Kerberos 4, but like Kerberos 4, only uses
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single DES@.
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You should only enable Kaserver support if you have needs for
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compatibility with an installed base of AFS machines.
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Kaserver can be turned on by adding this to the configuration file
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@example
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[kdc]
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enable-kaserver = yes
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@end example
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@node Remote administration, Password changing, Serving Kerberos 4/524/kaserver, Setting up a realm
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@section Remote administration
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The administration server, @command{kadmind}, can be started by
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@command{inetd} (which isn't recommended) or run as a normal daemon. If you
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want to start it from @command{inetd} you should add a line similar to the
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one below to your @file{/etc/inetd.conf}.
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@example
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kerberos-adm stream tcp nowait root /usr/heimdal/libexec/kadmind kadmind
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@end example
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You might need to add @samp{kerberos-adm} to your @file{/etc/services}
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as @samp{749/tcp}.
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Access to the administration server is controlled by an ACL file,
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(default @file{/var/heimdal/kadmind.acl}.) The file has the following
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syntax:
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@smallexample
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principal [priv1,priv2,...] [glob-pattern]
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@end smallexample
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The matching is from top to bottom for matching principals (and if given,
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glob-pattern). When there is a match, the access rights of that line are
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applied.
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The privileges you can assign to a principal are: @samp{add},
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@samp{change-password} (or @samp{cpw} for short), @samp{delete},
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@samp{get}, @samp{list}, and @samp{modify}, or the special privilege
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@samp{all}. All of these roughly correspond to the different commands
|
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in @command{kadmin}.
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If a @var{glob-pattern} is given on a line, it restricts the access
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rights for the principal to only apply for subjects that match the
|
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pattern. The patterns are of the same type as those used in shell
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globbing, see @url{none,,fnmatch(3)}.
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In the example below @samp{lha/admin} can change every principal in the
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database. @samp{jimmy/admin} can only modify principals that belong to
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the realm @samp{E.KTH.SE}. @samp{mille/admin} is working at the
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help desk, so he should only be able to change the passwords for single
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component principals (ordinary users). He will not be able to change any
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@samp{/admin} principal.
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@example
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lha/admin@@E.KTH.SE all
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jimmy/admin@@E.KTH.SE all *@@E.KTH.SE
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jimmy/admin@@E.KTH.SE all */*@@E.KTH.SE
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mille/admin@@E.KTH.SE change-password *@@E.KTH.SE
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@end example
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@node Password changing, Testing clients and servers, Remote administration, Setting up a realm
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@section Password changing
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To allow users to change their passwords, you should run @command{kpasswdd}.
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It is not run from @command{inetd}.
|
|
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|
You might need to add @samp{kpasswd} to your @file{/etc/services} as
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|
@samp{464/udp}. If your realm is not setup to use DNS, you might also
|
|
need to add a @samp{kpasswd_server} entry to the realm configuration
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in @file{/etc/krb5.conf} on client machines:
|
|
|
|
@example
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|
[realms]
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|
MY.REALM = @{
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|
kdc = my.kdc my.slave.kdc
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kpasswd_server = my.kdc
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@}
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@end example
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|
|
@subsection Password quality assurance
|
|
|
|
It is important that users have good passwords, both to make it harder
|
|
to guess them and to avoid off-line attacks (although
|
|
pre-authentication provides some defence against off-line attacks).
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|
To ensure that the users choose good passwords, you can enable
|
|
password quality controls in @command{kpasswdd} and @command{kadmind}.
|
|
The controls themselves are done in a shared library or an external
|
|
program that is used by @command{kpasswdd}. To configure in these
|
|
controls, add lines similar to the following to your
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|
@file{/etc/krb5.conf}:
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|
|
|
@example
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|
[password_quality]
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|
policies = external-check builtin:minimum-length modulename:policyname
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external_program = /bin/false
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policy_libraries = @var{library1.so} @var{library2.so}
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@end example
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|
|
|
In @samp{[password_quality]policies} the module name is optional if
|
|
the policy name is unique in all modules (members of
|
|
@samp{policy_libraries}). All built-in policies can be qualified with
|
|
a module name of @samp{builtin} to unambiguously specify the built-in
|
|
policy and not a policy by the same name from a loaded module.
|
|
|
|
The built-in policies are
|
|
|
|
@itemize @bullet
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|
|
|
@item external-check
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|
|
Executes the program specified by @samp{[password_quality]external_program}.
|
|
|
|
A number of key/value pairs are passed as input to the program, one per
|
|
line, ending with the string @samp{end}. The key/value lines are of
|
|
the form
|
|
@example
|
|
principal: @var{principal}
|
|
new-password: @var{password}
|
|
@end example
|
|
where @var{password} is the password to check for the previous
|
|
@var{principal}.
|
|
|
|
If the external application approves the password, it should return
|
|
@samp{APPROVED} on standard out and exit with exit code 0. If it
|
|
doesn't approve the password, an one line error message explaining the
|
|
problem should be returned on standard error and the application
|
|
should exit with exit code 0. In case of a fatal error, the
|
|
application should, if possible, print an error message on standard
|
|
error and exit with a non-zero error code.
|
|
|
|
@item minimum-length
|
|
|
|
The minimum length password quality check reads the configuration file
|
|
stanza @samp{[password_quality]min_length} and requires the password
|
|
to be at least this length.
|
|
|
|
@item character-class
|
|
|
|
The character-class password quality check reads the configuration
|
|
file stanza @samp{[password_quality]min_classes}. The policy requires
|
|
the password to have characters from at least that many character
|
|
classes. Default value if not given is 3.
|
|
|
|
The four different characters classes are, uppercase, lowercase,
|
|
number, special characters.
|
|
|
|
@end itemize
|
|
|
|
If you want to write your own shared object to check password
|
|
policies, see the manual page @manpage{kadm5_pwcheck,3}.
|
|
|
|
Code for a password quality checking function that uses the cracklib
|
|
library can be found in @file{lib/kadm5/sample_password_check.c} in
|
|
the source code distribution. It requires that the cracklib library
|
|
be built with the patch available at
|
|
@url{ftp://ftp.pdc.kth.se/pub/krb/src/cracklib.patch}.
|
|
|
|
A sample policy external program is included in
|
|
@file{lib/kadm5/check-cracklib.pl}.
|
|
|
|
If no password quality checking function is configured, the only check
|
|
performed is that the password is at least six characters long.
|
|
|
|
To check the password policy settings, use the command
|
|
@command{verify-password-quality} in @command{kadmin} program. The password
|
|
verification is only performed locally, on the client. It may be
|
|
convenient to set the environment variable @samp{KRB5_CONFIG} to point
|
|
to a test version of @file{krb5.conf} while you're testing the
|
|
@samp{[password_quality]} stanza that way.
|
|
|
|
@node Testing clients and servers, Slave Servers, Password changing, Setting up a realm
|
|
@section Testing clients and servers
|
|
|
|
Now you should be able to run all the clients and servers. Refer to the
|
|
appropriate man pages for information on how to use them.
|
|
|
|
@node Slave Servers, Incremental propagation, Testing clients and servers, Setting up a realm
|
|
@section Slave servers, Incremental propagation, Testing clients and servers, Setting up a realm
|
|
|
|
It is desirable to have at least one backup (slave) server in case the
|
|
master server fails. It is possible to have any number of such slave
|
|
servers but more than three usually doesn't buy much more redundancy.
|
|
|
|
All Kerberos servers for a realm must have the same database so that
|
|
they present the same service to the users. The
|
|
@pindex hprop
|
|
@command{hprop} program, running on the master, will propagate the database
|
|
to the slaves, running
|
|
@pindex hpropd
|
|
@command{hpropd} processes.
|
|
|
|
Every slave needs a database directory, the master key (if it was used
|
|
for the database) and a keytab with the principal
|
|
@samp{hprop/@var{hostname}}. Add the principal with the
|
|
@pindex ktutil
|
|
@command{ktutil} command and start
|
|
@pindex hpropd
|
|
@command{hpropd}, as follows:
|
|
|
|
@example
|
|
slave# ktutil get -p foo/admin hprop/`hostname`
|
|
slave# mkdir /var/heimdal
|
|
slave# hpropd
|
|
@end example
|
|
|
|
The master will use the principal @samp{kadmin/hprop} to authenticate to
|
|
the slaves. This principal should be added when running @kbd{kadmin -l
|
|
init} but if you do not have it in your database for whatever reason,
|
|
please add it with @kbd{kadmin -l add}.
|
|
|
|
Then run
|
|
@pindex hprop
|
|
@code{hprop} on the master:
|
|
|
|
@example
|
|
master# hprop slave
|
|
@end example
|
|
|
|
This was just an hands-on example to make sure that everything was
|
|
working properly. Doing it manually is of course the wrong way, and to
|
|
automate this you will want to start
|
|
@pindex hpropd
|
|
@command{hpropd} from @command{inetd} on the slave(s) and regularly run
|
|
@pindex hprop
|
|
@command{hprop} on the master to regularly propagate the database.
|
|
Starting the propagation once an hour from @command{cron} is probably a
|
|
good idea.
|
|
|
|
@node Incremental propagation, Encryption types and salting, Slave Servers, Setting up a realm
|
|
@section Incremental propagation
|
|
|
|
There is also a newer mechanism for
|
|
doing incremental propagation in Heimdal. Instead of sending the whole
|
|
database regularly, it sends the changes as they happen on the master to
|
|
the slaves. The master keeps track of all the changes by assigning a
|
|
version number to every change to the database. The slaves know which
|
|
was the latest version they saw and in this way it can be determined if
|
|
they are in sync or not. A log of all the changes is kept on the master,
|
|
and when a slave is at an older version than the oldest one in the
|
|
log, the whole database has to be sent.
|
|
|
|
Protocol-wise, all the slaves connect to the master and as a greeting
|
|
tell it the latest version that they have (@samp{IHAVE} message). The
|
|
master then responds by sending all the changes between that version and
|
|
the current version at the master (a series of @samp{FORYOU} messages)
|
|
or the whole database in a @samp{TELLYOUEVERYTHING} message. There is
|
|
also a keep-alive protocol that makes sure all slaves are up and running.
|
|
|
|
In addition on listening on the network to get connection from new
|
|
slaves, the ipropd-master also listens on a status unix
|
|
socket. kadmind and kpasswdd both open that socket when a transation
|
|
is done and written a notification to the socket. That cause
|
|
ipropd-master to check for new version in the log file. As a fallback in
|
|
case a notification is lost by the unix socket, the log file is
|
|
checked after 30 seconds of no event.
|
|
|
|
@subsection Configuring incremental propagation
|
|
|
|
The program that runs on the master is @command{ipropd-master} and all
|
|
clients run @command{ipropd-slave}.
|
|
|
|
Create the file @file{/var/heimdal/slaves} on the master containing all
|
|
the slaves that the database should be propagated to. Each line contains
|
|
the full name of the principal (for example
|
|
@samp{iprop/hemligare.foo.se@@FOO.SE}).
|
|
|
|
You should already have @samp{iprop/tcp} defined as 2121, in your
|
|
@file{/etc/services}. Otherwise, or if you need to use a different port
|
|
for some peculiar reason, you can use the @kbd{--port} option. This is
|
|
useful when you have multiple realms to distribute from one server.
|
|
|
|
Then you need to create those principals that you added in the
|
|
configuration file. Create one @samp{iprop/hostname} for the master and
|
|
for every slave.
|
|
|
|
|
|
@example
|
|
master# /usr/heimdal/sbin/ktutil get iprop/`hostname`
|
|
@end example
|
|
|
|
@example
|
|
slave# /usr/heimdal/sbin/ktutil get iprop/`hostname`
|
|
@end example
|
|
|
|
|
|
The next step is to start the @command{ipropd-master} process on the master
|
|
server. The @command{ipropd-master} listens on the UNIX domain socket
|
|
@file{/var/heimdal/signal} to know when changes have been made to the
|
|
database so they can be propagated to the slaves. There is also a
|
|
safety feature of testing the version number regularly (every 30
|
|
seconds) to see if it has been modified by some means that do not raise
|
|
this signal. Then, start @command{ipropd-slave} on all the slaves:
|
|
|
|
@example
|
|
master# /usr/heimdal/libexec/ipropd-master &
|
|
slave# /usr/heimdal/libexec/ipropd-slave master &
|
|
@end example
|
|
|
|
To manage the iprop log file you should use the @command{iprop-log}
|
|
command. With it you can dump, truncate and replay the logfile.
|
|
|
|
@node Encryption types and salting, Credential cache server - KCM, Incremental propagation, Setting up a realm
|
|
@section Encryption types and salting
|
|
@cindex Salting
|
|
@cindex Encryption types
|
|
|
|
The encryption types that the KDC is going to assign by default is
|
|
possible to change. Since the keys used for user authentication is
|
|
salted the encryption types are described together with the salt
|
|
strings.
|
|
|
|
Salting is used to make it harder to pre-calculate all possible
|
|
keys. Using a salt increases the search space to make it almost
|
|
impossible to pre-calculate all keys. Salting is the process of mixing a
|
|
public string (the salt) with the password, then sending it through an
|
|
encryption type specific string-to-key function that will output the
|
|
fixed size encryption key.
|
|
|
|
In Kerberos 5 the salt is determined by the encryption type, except in
|
|
some special cases.
|
|
|
|
In @code{des} there is the Kerberos 4 salt
|
|
(none at all) or the afs-salt (using the cell (realm in
|
|
AFS lingo)).
|
|
|
|
In @code{arcfour} (the encryption type that Microsoft Windows 2000 uses)
|
|
there is no salt. This is to be compatible with NTLM keys in Windows
|
|
NT 4.
|
|
|
|
@code{[kadmin]default_keys} in @file{krb5.conf} controls
|
|
what salting to use.
|
|
|
|
The syntax of @code{[kadmin]default_keys} is
|
|
@samp{[etype:]salt-type[:salt-string]}. @samp{etype} is the encryption
|
|
type (des-cbc-crc, arcfour-hmac-md5, aes256-cts-hmac-sha1-96),
|
|
@code{salt-type} is the type of salt (pw-salt or afs3-salt), and the
|
|
salt-string is the string that will be used as salt (remember that if
|
|
the salt is appended/prepended, the empty salt "" is the same thing as
|
|
no salt at all).
|
|
|
|
Common types of salting include
|
|
|
|
@itemize @bullet
|
|
@item @code{v4} (or @code{des:pw-salt:})
|
|
|
|
The Kerberos 4 salting is using no salt at all. Reason there is colon
|
|
at the end of the salt string is that it makes the salt the empty
|
|
string (same as no salt).
|
|
|
|
@item @code{v5} (or @code{pw-salt})
|
|
|
|
@code{pw-salt} uses the default salt for each encryption type is
|
|
specified for. If the encryption type @samp{etype} isn't given, all
|
|
default encryption will be used.
|
|
|
|
@item @code{afs3-salt}
|
|
|
|
@code{afs3-salt} is the salt that is used with Transarc kaserver. It's
|
|
the cell name appended to the password.
|
|
|
|
@end itemize
|
|
|
|
@node Credential cache server - KCM, Cross realm, Encryption types and salting, Setting up a realm
|
|
@section Credential cache server - KCM
|
|
@cindex KCM
|
|
@cindex Credential cache server
|
|
|
|
When KCM running is easy for users to switch between different
|
|
kerberos principals using @file{kswitch} or built in support in
|
|
application, like OpenSSH's GSSAPIClientIdentity.
|
|
|
|
Other advantages are that there is the long term credentials are not
|
|
written to disk and on reboot the credential is removed when kcm
|
|
process stopps running.
|
|
|
|
Configure the system startup script to start the kcm process,
|
|
@file{/usr/heimdal/libexec/kcm} and then configure the system to use kcm in @file{krb5.conf}.
|
|
|
|
@example
|
|
[libdefaults]
|
|
default_cc_type = KCM
|
|
@end example
|
|
|
|
Now when you run @command{kinit} it doesn't overwrite your existing
|
|
credentials but rather just add them to the set of
|
|
credentials. @command{klist -l} lists the credentials and the star
|
|
marks the default credential.
|
|
|
|
@example
|
|
$ kinit lha@@KTH.SE
|
|
lha@@KTH.SE's Password:
|
|
$ klist -l
|
|
Name Cache name Expires
|
|
lha@@KTH.SE 0 Nov 22 23:09:40 *
|
|
lha@@SU.SE Initial default ccache Nov 22 14:14:24
|
|
@end example
|
|
|
|
When switching between credentials you can use @command{kswitch}.
|
|
|
|
@example
|
|
$ kswitch -i
|
|
Principal
|
|
1 lha@@KTH.SE
|
|
2 lha@@SU.SE
|
|
Select number: 2
|
|
@end example
|
|
|
|
After switching, a new set of credentials are used as default.
|
|
|
|
@example
|
|
$ klist -l
|
|
Name Cache name Expires
|
|
lha@@SU.SE Initial default ccache Nov 22 14:14:24 *
|
|
lha@@KTH.SE 0 Nov 22 23:09:40
|
|
@end example
|
|
|
|
Som applications, like openssh with Simon Wilkinsons patch applied,
|
|
support specifiying that credential to use. The example below will
|
|
login to the host computer.kth.se using lha@@KTH.SE (not the current
|
|
default credential).
|
|
|
|
@example
|
|
$ ssh \
|
|
-o GSSAPIAuthentication=yes \
|
|
-o GSSAPIKeyExchange=yes \
|
|
-o GSSAPIClientIdentity=lha@@KTH.SE \
|
|
computer.kth.se
|
|
@end example
|
|
|
|
|
|
|
|
@node Cross realm, Transit policy, Credential cache server - KCM, Setting up a realm
|
|
@section Cross realm
|
|
@cindex Cross realm
|
|
|
|
Suppose you reside in the realm @samp{MY.REALM}, how do you
|
|
authenticate to a server in @samp{OTHER.REALM}? Having valid tickets in
|
|
@samp{MY.REALM} allows you to communicate with Kerberised services in that
|
|
realm. However, the computer in the other realm does not have a secret
|
|
key shared with the Kerberos server in your realm.
|
|
|
|
It is possible to share keys between two realms that trust each
|
|
other. When a client program, such as @command{telnet} or @command{ssh},
|
|
finds that the other computer is in a different realm, it will try to
|
|
get a ticket granting ticket for that other realm, but from the local
|
|
Kerberos server. With that ticket granting ticket, it will then obtain
|
|
service tickets from the Kerberos server in the other realm.
|
|
|
|
For a two way trust between @samp{MY.REALM} and @samp{OTHER.REALM}
|
|
add the following principals to each realm. The principals should be
|
|
@samp{krbtgt/OTHER.REALM@@MY.REALM} and
|
|
@samp{krbtgt/MY.REALM@@OTHER.REALM} in @samp{MY.REALM}, and
|
|
@samp{krbtgt/MY.REALM@@OTHER.REALM} and
|
|
@samp{krbtgt/OTHER.REALM@@MY.REALM}in @samp{OTHER.REALM}.
|
|
|
|
In Kerberos 5 the trust can be configured to be one way. So that
|
|
users from @samp{MY.REALM} can authenticate to services in
|
|
@samp{OTHER.REALM}, but not the opposite. In the example above, the
|
|
@samp{krbtgt/MY.REALM@@OTHER.REALM} then should be removed.
|
|
|
|
The two principals must have the same key, key version number, and the
|
|
same set of encryption types. Remember to transfer the two keys in a
|
|
safe manner.
|
|
|
|
@example
|
|
vr$ klist
|
|
Credentials cache: FILE:/tmp/krb5cc_913.console
|
|
Principal: lha@@E.KTH.SE
|
|
|
|
Issued Expires Principal
|
|
May 3 13:55:52 May 3 23:55:54 krbtgt/E.KTH.SE@@E.KTH.SE
|
|
|
|
vr$ telnet -l lha hummel.it.su.se
|
|
Trying 2001:6b0:5:1095:250:fcff:fe24:dbf...
|
|
Connected to hummel.it.su.se.
|
|
Escape character is '^]'.
|
|
Waiting for encryption to be negotiated...
|
|
[ Trying mutual KERBEROS5 (host/hummel.it.su.se@@SU.SE)... ]
|
|
[ Kerberos V5 accepts you as ``lha@@E.KTH.SE'' ]
|
|
Encryption negotiated.
|
|
Last login: Sat May 3 14:11:47 from vr.l.nxs.se
|
|
hummel$ exit
|
|
|
|
vr$ klist
|
|
Credentials cache: FILE:/tmp/krb5cc_913.console
|
|
Principal: lha@@E.KTH.SE
|
|
|
|
Issued Expires Principal
|
|
May 3 13:55:52 May 3 23:55:54 krbtgt/E.KTH.SE@@E.KTH.SE
|
|
May 3 13:55:56 May 3 23:55:54 krbtgt/SU.SE@@E.KTH.SE
|
|
May 3 14:10:54 May 3 23:55:54 host/hummel.it.su.se@@SU.SE
|
|
|
|
@end example
|
|
|
|
@node Transit policy, Setting up DNS, Cross realm, Setting up a realm
|
|
@section Transit policy
|
|
@cindex Transit policy
|
|
|
|
Under some circumstances, you may not wish to set up direct
|
|
cross-realm trust with every realm to which you wish to authenticate
|
|
or from which you wish to accept authentications. Kerberos supports
|
|
multi-hop cross-realm trust where a client principal in realm A
|
|
authenticates to a service in realm C through a realm B with which
|
|
both A and C have cross-realm trust relationships. In this situation,
|
|
A and C need not set up cross-realm principals between each other.
|
|
|
|
If you want to use cross-realm authentication through an intermediate
|
|
realm, it must be explicitly allowed by either the KDCs for the realm
|
|
to which the client is authenticating (in this case, realm C), or the
|
|
server receiving the request. This is done in @file{krb5.conf} in the
|
|
@code{[capaths]} section.
|
|
|
|
In addition, the client in realm A need to be configured to know how
|
|
to reach realm C via realm B. This can be done either on the client or
|
|
via KDC configuration in the KDC for realm A.
|
|
|
|
@subsection Allowing cross-realm transits
|
|
|
|
When the ticket transits through a realm to another realm, the
|
|
destination realm adds its peer to the "transited-realms" field in the
|
|
ticket. The field is unordered, since there is no way to know if know
|
|
if one of the transited-realms changed the order of the list. For the
|
|
authentication to be accepted by the final destination realm, all of
|
|
the transited realms must be listed as trusted in the @code{[capaths]}
|
|
configuration, either in the KDC for the destination realm or on the
|
|
server receiving the authentication.
|
|
|
|
The syntax for @code{[capaths]} section is:
|
|
|
|
@example
|
|
[capaths]
|
|
CLIENT-REALM = @{
|
|
SERVER-REALM = PERMITTED-CROSS-REALMS ...
|
|
@}
|
|
@end example
|
|
|
|
In the following example, the realm @code{STACKEN.KTH.SE} only has
|
|
direct cross-realm set up with @code{KTH.SE}. @code{KTH.SE} has
|
|
direct cross-realm set up with @code{STACKEN.KTH.SE} and @code{SU.SE}.
|
|
@code{DSV.SU.SE} only has direct cross-realm set up with @code{SU.SE}.
|
|
The goal is to allow principals in the @code{DSV.SU.SE} or
|
|
@code{SU.SE} realms to authenticate to services in
|
|
@code{STACKEN.KTH.SE}. This is done with the following
|
|
@code{[capaths]} entry on either the server accepting authentication
|
|
or on the KDC for @code{STACKEN.KTH.SE}.
|
|
|
|
@example
|
|
[capaths]
|
|
SU.SE = @{
|
|
STACKEN.KTH.SE = KTH.SE
|
|
@}
|
|
DSV.SU.SE = @{
|
|
STACKEN.KTH.SE = SU.SE KTH.SE
|
|
@}
|
|
@end example
|
|
|
|
The first entry allows cross-realm authentication from clients in
|
|
@code{SU.SE} transiting through @code{KTH.SE} to
|
|
@code{STACKEN.KTH.SE}. The second entry allows cross-realm
|
|
authentication from clients in @code{DSV.SU.SE} transiting through
|
|
both @code{SU.SE} and @code{KTH.SE} to @code{STACKEN.KTH.SE}.
|
|
|
|
Be careful of which realm goes where; it's easy to put realms in the
|
|
wrong place. The block is tagged with the client realm (the realm of
|
|
the principal authenticating), and the realm before the equal sign is
|
|
the final destination realm: the realm to which the client is
|
|
authenticating. After the equal sign go all the realms that the
|
|
client transits through.
|
|
|
|
The order of the @code{PERMITTED-CROSS-REALMS} is not important when
|
|
doing transit cross realm verification.
|
|
|
|
@subsection Configuring client cross-realm transits
|
|
|
|
The @code{[capaths]} section is also used for another purpose: to tell
|
|
clients which realm to transit through to reach a realm with which
|
|
their local realm does not have cross-realm trust. This can be done
|
|
by either putting a @code{[capaths]} entry in the configuration of the
|
|
client or by putting the entry in the configuration of the KDC for the
|
|
client's local realm. In the latter case, the KDC will then hand back
|
|
a referral to the client when the client requests a cross-realm ticket
|
|
to the destination realm, telling the client to try to go through an
|
|
intermediate realm.
|
|
|
|
For client configuration, the order of @code{PERMITTED-CROSS-REALMS}
|
|
is significant, since only the first realm in this section (after the
|
|
equal sign) is used by the client.
|
|
|
|
For example, again consider the @code{[capaths]} entry above for the
|
|
case of a client in the @code{SU.SE} realm, and assume that the client
|
|
or the @code{SU.SE} KDC has that @code{[capaths]} entry. If the
|
|
client attempts to authenticate to a service in the
|
|
@code{STACKEN.KTH.SE} realm, that entry says to first authenticate
|
|
cross-realm to the @code{KTH.SE} realm (the first realm listed in the
|
|
@code{PERMITTED-CROSS-REALMS} section), and then from there to
|
|
@code{STACKEN.KTH.SE}.
|
|
|
|
Each entry in @code{[capaths]} can only give the next hop, since only
|
|
the first realm in @code{PERMITTED-CROSS-REALMS} is used. If, for
|
|
instance, a client in @code{DSV.SU.SE} had a @code{[capaths]}
|
|
configuration as above but without the first block for @code{SU.SE},
|
|
they would not be able to reach @code{STACKEN.KTH.SE}. They would get
|
|
as far as @code{SU.SE} based on the @code{DSV.SU.SE} entry in
|
|
@code{[capaths]} and then attempt to go directly from there to
|
|
@code{STACKEN.KTH.SE} and get stuck (unless, of course, the
|
|
@code{SU.SE} KDC had the additional entry required to tell the client
|
|
to go through @code{KTH.SE}).
|
|
|
|
@subsection Active Directory forest example
|
|
|
|
One common place where a @code{[capaths]} configuration is desirable
|
|
is with Windows Active Directory forests. One common Active Directory
|
|
configuration is to have one top-level Active Directory realm but then
|
|
divide systems, services, and users into child realms (perhaps based
|
|
on organizational unit). One generally establishes cross-realm trust
|
|
only with the top-level realm, and then uses transit policy to permit
|
|
authentications to and from the child realms.
|
|
|
|
For example, suppose an organization has a Heimdal realm
|
|
@code{EXAMPLE.COM}, a Windows Active Directory realm
|
|
@code{WIN.EXAMPLE.COM}, and then child Active Directory realms
|
|
@code{ENGR.WIN.EXAMPLE.COM} and @code{SALES.WIN.EXAMPLE.COM}. The
|
|
goal is to allow users in any of these realms to authenticate to
|
|
services in any of these realms. The @code{EXAMPLE.COM} KDC (and
|
|
possibly client) configuration should therefore contain a
|
|
@code{[capaths]} section as follows:
|
|
|
|
@example
|
|
[capaths]
|
|
ENGR.WIN.EXAMPLE.COM = @{
|
|
EXAMPLE.COM = WIN.EXAMPLE.COM
|
|
@}
|
|
SALES.WIN.EXAMPLE.COM = @{
|
|
EXAMPLE.COM = WIN.EXAMPLE.COM
|
|
@}
|
|
EXAMPLE.COM = @{
|
|
ENGR.WIN.EXAMPLE.COM = WIN.EXAMPLE.COM
|
|
SALES.WIN.EXAMPLE.COM = WIN.EXAMPLE.COM
|
|
@}
|
|
@end example
|
|
|
|
The first two blocks allow clients in the @code{ENGR.WIN.EXAMPLE.COM}
|
|
and @code{SALES.WIN.EXAMPLE.COM} realms to authenticate to services in
|
|
the @code{EXAMPLE.COM} realm. The third block tells the client (or
|
|
tells the KDC to tell the client via referrals) to transit through
|
|
@code{WIN.EXAMPLE.COM} to reach these realms. Both sides of the
|
|
configuration are needed for bi-directional transited cross-realm
|
|
authentication.
|
|
|
|
@c To test the cross realm configuration, use:
|
|
@c kmumble transit-check client server transit-realms ...
|
|
|
|
@node Setting up DNS, Using LDAP to store the database, Transit policy, Setting up a realm
|
|
@section Setting up DNS
|
|
@cindex Setting up DNS
|
|
|
|
@subsection Using DNS to find KDC
|
|
|
|
If there is information about where to find the KDC or kadmind for a
|
|
realm in the @file{krb5.conf} for a realm, that information will be
|
|
preferred, and DNS will not be queried.
|
|
|
|
Heimdal will try to use DNS to find the KDCs for a realm. First it
|
|
will try to find a @code{SRV} resource record (RR) for the realm. If no
|
|
SRV RRs are found, it will fall back to looking for an @code{A} RR for
|
|
a machine named kerberos.REALM, and then kerberos-1.REALM, etc
|
|
|
|
Adding this information to DNS minimises the client configuration (in
|
|
the common case, resulting in no configuration needed) and allows the
|
|
system administrator to change the number of KDCs and on what machines
|
|
they are running without caring about clients.
|
|
|
|
The downside of using DNS is that the client might be fooled to use the
|
|
wrong server if someone fakes DNS replies/data, but storing the IP
|
|
addresses of the KDC on all the clients makes it very hard to change
|
|
the infrastructure.
|
|
|
|
An example of the configuration for the realm @code{EXAMPLE.COM}:
|
|
|
|
@example
|
|
|
|
$ORIGIN example.com.
|
|
_kerberos._tcp SRV 10 1 88 kerberos.example.com.
|
|
_kerberos._udp SRV 10 1 88 kerberos.example.com.
|
|
_kerberos._tcp SRV 10 1 88 kerberos-1.example.com.
|
|
_kerberos._udp SRV 10 1 88 kerberos-1.example.com.
|
|
_kpasswd._udp SRV 10 1 464 kerberos.example.com.
|
|
_kerberos-adm._tcp SRV 10 1 749 kerberos.example.com.
|
|
|
|
@end example
|
|
|
|
More information about DNS SRV resource records can be found in
|
|
RFC-2782 (A DNS RR for specifying the location of services (DNS SRV)).
|
|
|
|
@subsection Using DNS to map hostname to Kerberos realm
|
|
|
|
Heimdal also supports a way to lookup a realm from a hostname. This to
|
|
minimise configuration needed on clients. Using this has the drawback
|
|
that clients can be redirected by an attacker to realms within the
|
|
same cross realm trust and made to believe they are talking to the
|
|
right server (since Kerberos authentication will succeed).
|
|
|
|
An example configuration that informs clients that for the realms
|
|
it.example.com and srv.example.com, they should use the realm
|
|
EXAMPLE.COM:
|
|
|
|
@example
|
|
|
|
$ORIGIN example.com.
|
|
_kerberos.it TXT "EXAMPLE.COM"
|
|
_kerberos.srv TXT "EXAMPLE.COM"
|
|
|
|
@end example
|
|
|
|
@node Using LDAP to store the database, Providing Kerberos credentials to servers and programs, Setting up DNS, Setting up a realm
|
|
@section Using LDAP to store the database
|
|
@cindex Using the LDAP backend
|
|
|
|
This document describes how to install the LDAP backend for
|
|
Heimdal. Note that before attempting to configure such an
|
|
installation, you should be aware of the implications of storing
|
|
private information (such as users' keys) in a directory service
|
|
primarily designed for public information. Nonetheless, with a
|
|
suitable authorisation policy, it is possible to set this up in a
|
|
secure fashion. A knowledge of LDAP, Kerberos, and C is necessary to
|
|
install this backend. The HDB schema was devised by Leif Johansson.
|
|
|
|
This assumes, OpenLDAP 2.3 or later.
|
|
|
|
Requirements:
|
|
|
|
@itemize @bullet
|
|
|
|
@item
|
|
A current release of Heimdal, configured with
|
|
@code{--with-openldap=/usr/local} (adjust according to where you have
|
|
installed OpenLDAP).
|
|
|
|
You can verify that you manage to configure LDAP support by running
|
|
@file{kdc --builtin-hdb}, and checking that @samp{ldap:} is one entry
|
|
in the list.
|
|
|
|
Its also possible to configure the ldap backend as a shared module,
|
|
see option --hdb-openldap-module to configure.
|
|
|
|
@item
|
|
Configure OpenLDAP with @kbd{--enable-local} to enable the local transport.
|
|
|
|
@item
|
|
Add the hdb schema to the LDAP server, it's included in the source-tree
|
|
in @file{lib/hdb/hdb.schema}. Example from slapd.conf:
|
|
|
|
@example
|
|
include /usr/local/etc/openldap/schema/hdb.schema
|
|
@end example
|
|
|
|
@item
|
|
Configure the LDAP server ACLs to accept writes from clients over the
|
|
local transport. For example:
|
|
|
|
@example
|
|
access to *
|
|
by dn.exact="uid=heimdal,dc=services,dc=example,dc=com" write
|
|
...
|
|
|
|
authz-regexp "gidNumber=.*\\\+uidNumber=0,cn=peercred,cn=external,cn=auth''
|
|
"uid=heimdal,dc=services,dc=example,dc=com"
|
|
|
|
@end example
|
|
|
|
The sasl-regexp is for mapping between the SASL/EXTERNAL and a user in
|
|
a tree. The user that the key is mapped to should be have a
|
|
krb5Principal aux object with krb5PrincipalName set so that the
|
|
``creator'' and ``modifier'' is right in @file{kadmin}.
|
|
|
|
Another option is to create an admins group and add the dn to that
|
|
group.
|
|
|
|
Since Heimdal talks to the LDAP server over a UNIX domain socket, and
|
|
uses external sasl authentication, it's not possible to require
|
|
security layer quality (ssf in cyrus-sasl lingo). So that requirement
|
|
has to be turned off in OpenLDAP @command{slapd} configuration file
|
|
@file{slapd.conf}.
|
|
|
|
@example
|
|
sasl-secprops minssf=0
|
|
@end example
|
|
|
|
@item
|
|
|
|
Start @command{slapd} with the local listener (as well as the default TCP/IP
|
|
listener on port 389) as follows:
|
|
|
|
@example
|
|
slapd -h "ldapi:/// ldap:///"
|
|
@end example
|
|
|
|
Note: These is a bug in @command{slapd} where it appears to corrupt the krb5Key
|
|
binary attribute on shutdown. This may be related to our use of the V3
|
|
schema definition syntax instead of the old UMich-style, V2 syntax.
|
|
|
|
@item
|
|
You should specify the distinguished name under which your
|
|
principals will be stored in @file{krb5.conf}. Also you need to
|
|
enter the path to the kadmin acl file:
|
|
|
|
|
|
@example
|
|
[kdc]
|
|
database = @{
|
|
dbname = ldap:ou=KerberosPrincipals,dc=example,dc=com
|
|
hdb-ldap-structural-object = inetOrgPerson
|
|
acl_file = /path/to/kadmind.acl
|
|
mkey_file = /path/to/mkey
|
|
@}
|
|
@end example
|
|
|
|
@samp{mkey_file} can be excluded if you feel that you trust your ldap
|
|
directory to have the raw keys inside it. The
|
|
hdb-ldap-structural-object is not necessary if you do not need Samba
|
|
comatibility.
|
|
|
|
|
|
|
|
@item
|
|
Once you have built Heimdal and started the LDAP server, run kadmin
|
|
(as usual) to initialise the database. Note that the instructions for
|
|
stashing a master key are as per any Heimdal installation.
|
|
|
|
@example
|
|
kdc# kadmin -l
|
|
kadmin> init EXAMPLE.COM
|
|
Realm max ticket life [unlimited]:
|
|
Realm max renewable ticket life [unlimited]:
|
|
kadmin> add lukeh
|
|
Max ticket life [1 day]:
|
|
Max renewable life [1 week]:
|
|
Principal expiration time [never]:
|
|
Password expiration time [never]:
|
|
Attributes []:
|
|
lukeh@@EXAMPLE.COM's Password:
|
|
Verifying password - lukeh@@EXAMPLE.COM's Password:
|
|
kadmin> exit
|
|
@end example
|
|
|
|
Verify that the principal database has indeed been stored in the
|
|
directory with the following command:
|
|
|
|
@example
|
|
kdc# ldapsearch -L -h localhost -D cn=manager \
|
|
-w secret -b ou=KerberosPrincipals,dc=example,dc=com \
|
|
'objectclass=krb5KDCEntry'
|
|
@end example
|
|
|
|
@item
|
|
Now consider adding indexes to the database to speed up the access, at
|
|
least theses should be added to slapd.conf.
|
|
|
|
@example
|
|
index objectClass eq
|
|
index cn eq,sub,pres
|
|
index uid eq,sub,pres
|
|
index displayName eq,sub,pres
|
|
index krb5PrincipalName eq
|
|
@end example
|
|
|
|
@end itemize
|
|
|
|
@subsection smbk5pwd overlay
|
|
|
|
The smbk5pwd overlay, updates the krb5Key and krb5KeyVersionNumber
|
|
appropriately when it receives an LDAP Password change Extended
|
|
Operation:
|
|
|
|
@url{http://www.openldap.org/devel/cvsweb.cgi/contrib/slapd-modules/smbk5pwd/README?hideattic=1&sortbydate=0}
|
|
|
|
@subsection Troubleshooting guide
|
|
|
|
@url{https://sec.miljovern.no/bin/view/Info/TroubleshootingGuide}
|
|
|
|
|
|
@subsection Using Samba LDAP password database
|
|
@cindex Samba
|
|
|
|
@c @node Using Samba LDAP password database, Providing Kerberos credentials to servers and programs, Using LDAP to store the database, Setting up a realm
|
|
@c @section Using Samba LDAP password database
|
|
|
|
The Samba domain and the Kerberos realm can have different names since
|
|
arcfour's string to key functions principal/realm independent. So now
|
|
will be your first and only chance name your Kerberos realm without
|
|
needing to deal with old configuration files.
|
|
|
|
First, you should set up Samba and get that working with LDAP backend.
|
|
|
|
Now you can proceed as in @xref{Using LDAP to store the database}.
|
|
Heimdal will pick up the Samba LDAP entries if they are in the same
|
|
search space as the Kerberos entries.
|
|
|
|
@node Providing Kerberos credentials to servers and programs, Setting up PK-INIT, Using LDAP to store the database, Setting up a realm
|
|
@section Providing Kerberos credentials to servers and programs
|
|
|
|
Some services require Kerberos credentials when they start to make
|
|
connections to other services or need to use them when they have started.
|
|
|
|
The easiest way to get tickets for a service is to store the key in a
|
|
keytab. Both ktutil get and kadmin ext can be used to get a
|
|
keytab. ktutil get is better in that way it changes the key/password
|
|
for the user. This is also the problem with ktutil. If ktutil is used
|
|
for the same service principal on several hosts, they keytab will only
|
|
be useful on the last host. In that case, run the extract command on
|
|
one host and then securely copy the keytab around to all other hosts
|
|
that need it.
|
|
|
|
@example
|
|
host# ktutil -k /etc/krb5-service.keytab \
|
|
get -p lha/admin@@EXAMPLE.ORG service-principal@@EXAMPLE.ORG
|
|
lha/admin@@EXAMPLE.ORG's Password:
|
|
@end example
|
|
|
|
To get a Kerberos credential file for the service, use kinit in the
|
|
@kbd{--keytab} mode. This will not ask for a password but instead fetch the
|
|
key from the keytab.
|
|
|
|
@example
|
|
service@@host$ kinit --cache=/var/run/service_krb5_cache \
|
|
--keytab=/etc/krb5-service.keytab \
|
|
service-principal@@EXAMPLE.ORG
|
|
@end example
|
|
|
|
Long running services might need credentials longer then the
|
|
expiration time of the tickets. kinit can run in a mode that refreshes
|
|
the tickets before they expire. This is useful for services that write
|
|
into AFS and other distributed file systems using Kerberos. To run the
|
|
long running script, just append the program and arguments (if any)
|
|
after the principal. kinit will stop refreshing credentials and remove
|
|
the credentials when the script-to-start-service exits.
|
|
|
|
@example
|
|
service@@host$ kinit --cache=/var/run/service_krb5_cache \
|
|
--keytab=/etc/krb5-service.keytab \
|
|
service-principal@@EXAMPLE.ORG \
|
|
script-to-start-service argument1 argument2
|
|
@end example
|
|
|
|
|
|
@node Setting up PK-INIT, Debugging Kerberos problems, Providing Kerberos credentials to servers and programs, Setting up a realm
|
|
@section Setting up PK-INIT
|
|
|
|
PK-INIT leverages an existing PKI (public key infrastructure), using
|
|
certificates to get the initial ticket (usually the krbtgt
|
|
ticket-granting ticket).
|
|
|
|
To use PK-INIT you must first have a PKI. If you don't have one, it is
|
|
time to create it. You should first read the whole chapter of the
|
|
document to see the requirements imposed on the CA software.
|
|
|
|
A mapping between the PKI certificate and what principals that
|
|
certificate is allowed to use must exist. There are several ways to do
|
|
this. The administrator can use a configuration file, store the
|
|
principal in the SubjectAltName extension of the certificate, or store
|
|
the mapping in the principals entry in the kerberos database.
|
|
|
|
@section Certificates
|
|
|
|
This section documents the requirements on the KDC and client
|
|
certificates and the format used in the id-pkinit-san OtherName
|
|
extention.
|
|
|
|
@subsection KDC certificate
|
|
|
|
The certificate for the KDC has serveral requirements.
|
|
|
|
First, the certificate should have an Extended Key Usage (EKU)
|
|
id-pkkdcekuoid (1.3.6.1.5.2.3.5) set. Second, there must be a
|
|
subjectAltName otherName using OID id-pkinit-san (1.3.6.1.5.2.2) in
|
|
the type field and a DER encoded KRB5PrincipalName that matches the
|
|
name of the TGS of the target realm. Also, if the certificate has a
|
|
nameConstraints extention with a Generalname with dNSName or iPAdress,
|
|
it must match the hostname or adress of the KDC.
|
|
|
|
The client is not required by the standard to check the server
|
|
certificate for this information if the client has external
|
|
information confirming which certificate the KDC is supposed to be
|
|
using. However, adding this information to the KDC certificate removes
|
|
the need to specially configure the client to recognize the KDC
|
|
certificate.
|
|
|
|
Remember that if the client would accept any certificate as the KDC's
|
|
certificate, the client could be fooled into trusting something that
|
|
isn't a KDC and thus expose the user to giving away information (like
|
|
a password or other private information) that it is supposed to keep
|
|
secret.
|
|
|
|
@subsection Client certificate
|
|
|
|
The client certificate may need to have a EKU id-pkekuoid
|
|
(1.3.6.1.5.2.3.4) set depending on the certifiate on the KDC.
|
|
|
|
It possible to store the principal (if allowed by the KDC) in the
|
|
certificate and thus delegate responsibility to do the mapping between
|
|
certificates and principals to the CA.
|
|
|
|
This behavior is controlled by KDC configuration option:
|
|
|
|
@example
|
|
[kdc]
|
|
pkinit_principal_in_certificate = yes
|
|
@end example
|
|
|
|
@subsubsection Using KRB5PrincipalName in id-pkinit-san
|
|
|
|
The OtherName extention in the GeneralName is used to do the mapping
|
|
between certificate and principal. For the KDC certificate, this
|
|
stores the krbtgt principal name for that KDC. For the client
|
|
certificate, this stores the principal for which that certificate is
|
|
allowed to get tickets.
|
|
|
|
The principal is stored in a SubjectAltName in the certificate using
|
|
OtherName. The OID in the type is id-pkinit-san.
|
|
|
|
@example
|
|
id-pkinit-san OBJECT IDENTIFIER ::= @{ iso (1) org (3) dod (6)
|
|
internet (1) security (5) kerberosv5 (2) 2 @}
|
|
@end example
|
|
|
|
The data part of the OtherName is filled with the following DER
|
|
encoded ASN.1 structure:
|
|
|
|
@example
|
|
KRB5PrincipalName ::= SEQUENCE @{
|
|
realm [0] Realm,
|
|
principalName [1] PrincipalName
|
|
@}
|
|
@end example
|
|
|
|
where Realm and PrincipalName is defined by the Kerberos ASN.1
|
|
specification.
|
|
|
|
@section Naming certificate using hx509
|
|
|
|
hx509 is the X.509 software used in Heimdal to handle
|
|
certificates. hx509 supports several different syntaxes for specifying
|
|
certificate files or formats. Several formats may be used: PEM,
|
|
certificates embedded in PKCS#12 files, certificates embedded in
|
|
PKCS#11 devices, and raw DER encoded certificates.
|
|
|
|
Those formats may be specified as follows:
|
|
|
|
@table @asis
|
|
|
|
@item DIR:
|
|
|
|
DIR specifies a directory which contains certificates in the DER or
|
|
PEM format.
|
|
|
|
The main feature of DIR is that the directory is read on demand when
|
|
iterating over certificates. This allows applications, in some
|
|
situations, to avoid having to store all certificates in memory. It's
|
|
very useful for tests that iterate over large numbers of certificates.
|
|
|
|
The syntax is:
|
|
|
|
@example
|
|
DIR:/path/to/der/files
|
|
@end example
|
|
|
|
@item FILE:
|
|
|
|
FILE: specifies a file that contains a certificate or private key.
|
|
The file can be either a PEM (openssl) file or a raw DER encoded
|
|
certificate. If it's a PEM file, it can contain several keys and
|
|
certificates and the code will try to match the private key and
|
|
certificate together. Multiple files may be specified, separated by
|
|
commas.
|
|
|
|
It's useful to have one PEM file that contains all the trust anchors.
|
|
|
|
The syntax is:
|
|
|
|
@example
|
|
FILE:certificate.pem,private-key.key,other-cert.pem,....
|
|
@end example
|
|
|
|
@item PKCS11:
|
|
|
|
PKCS11: is used to handle smartcards via PKCS#11 drivers, such as
|
|
soft-token, opensc, or muscle. The argument specifies a shared object
|
|
that implements the PKCS#11 API. The default is to use all slots on
|
|
the device/token.
|
|
|
|
The syntax is:
|
|
|
|
@example
|
|
PKCS11:shared-object.so
|
|
@end example
|
|
|
|
@item PKCS12:
|
|
|
|
PKCS12: is used to handle PKCS#12 files. PKCS#12 files commonly have
|
|
the extension pfx or p12.
|
|
|
|
The syntax is:
|
|
|
|
@example
|
|
PKCS12:/path/to/file.pfx
|
|
@end example
|
|
|
|
@end table
|
|
|
|
@section Configure the Kerberos software
|
|
|
|
First configure the client's trust anchors and what parameters to
|
|
verify. See the subsections below for how to do that. Then, you can
|
|
use kinit to get yourself tickets. For example:
|
|
|
|
@example
|
|
$ kinit -C FILE:$HOME/.certs/lha.crt,$HOME/.certs/lha.key lha@@EXAMPLE.ORG
|
|
Enter your private key passphrase:
|
|
: lha@@nutcracker ; klist
|
|
Credentials cache: FILE:/tmp/krb5cc_19100a
|
|
Principal: lha@@EXAMPLE.ORG
|
|
|
|
Issued Expires Principal
|
|
Apr 20 02:08:08 Apr 20 12:08:08 krbtgt/EXAMPLE.ORG@@EXAMPLE.ORG
|
|
@end example
|
|
|
|
Using PKCS#11 it can look like this instead:
|
|
|
|
@example
|
|
$ kinit -C PKCS11:/usr/heimdal/lib/hx509.so lha@@EXAMPLE.ORG
|
|
PIN code for SoftToken (slot):
|
|
$ klist
|
|
Credentials cache: API:4
|
|
Principal: lha@@EXAMPLE.ORG
|
|
|
|
Issued Expires Principal
|
|
Mar 26 23:40:10 Mar 27 09:40:10 krbtgt/EXAMPLE.ORG@@EXAMPLE.ORG
|
|
@end example
|
|
|
|
TODO: Write about the KDC.
|
|
|
|
@section Configure the client
|
|
|
|
@example
|
|
[appdefaults]
|
|
pkinit_anchors = FILE:/path/to/trust-anchors.pem
|
|
|
|
[realms]
|
|
EXAMPLE.COM = @{
|
|
pkinit_require_eku = true
|
|
pkinit_require_krbtgt_otherName = true
|
|
pkinit_win2k = no
|
|
pkinit_win2k_require_binding = yes
|
|
@}
|
|
|
|
@end example
|
|
|
|
@section Configure the KDC
|
|
|
|
@example
|
|
[kdc]
|
|
enable-pkinit = yes
|
|
pkinit_identity = FILE:/secure/kdc.crt,/secure/kdc.key
|
|
pkinit_anchors = FILE:/path/to/trust-anchors.pem
|
|
pkinit_pool = PKCS12:/path/to/useful-intermediate-certs.pfx
|
|
pkinit_pool = FILE:/path/to/other-useful-intermediate-certs.pem
|
|
pkinit_allow_proxy_certificate = no
|
|
pkinit_win2k_require_binding = yes
|
|
pkinit_principal_in_certificate = no
|
|
@end example
|
|
|
|
@subsection Using pki-mapping file
|
|
|
|
Note that the file name is space sensitive.
|
|
|
|
@example
|
|
# cat /var/heimdal/pki-mapping
|
|
# comments starts with #
|
|
lha@@EXAMPLE.ORG:C=SE,O=Stockholm universitet,CN=Love,UID=lha
|
|
lha@@EXAMPLE.ORG:CN=Love,UID=lha
|
|
@end example
|
|
|
|
@subsection Using the Kerberos database
|
|
|
|
@section Use hxtool to create certificates
|
|
|
|
@subsection Generate certificates
|
|
|
|
First, you need to generate a CA certificate. This example creates a
|
|
CA certificate that will be valid for 10 years.
|
|
|
|
You need to change --subject in the command below to something
|
|
appropriate for your site.
|
|
|
|
@example
|
|
hxtool issue-certificate \
|
|
--self-signed \
|
|
--issue-ca \
|
|
--generate-key=rsa \
|
|
--subject="CN=CA,DC=test,DC=h5l,DC=se" \
|
|
--lifetime=10years \
|
|
--certificate="FILE:ca.pem"
|
|
@end example
|
|
|
|
The KDC needs to have a certificate, so generate a certificate of the
|
|
type ``pkinit-kdc'' and set the PK-INIT specifial SubjectAltName to the
|
|
name of the krbtgt of the realm.
|
|
|
|
You need to change --subject and --pk-init-principal in the command
|
|
below to something appropriate for your site.
|
|
|
|
@example
|
|
hxtool issue-certificate \
|
|
--ca-certificate=FILE:ca.pem \
|
|
--generate-key=rsa \
|
|
--type="pkinit-kdc" \
|
|
--pk-init-principal="krbtgt/TEST.H5L.SE@@TEST.H5L.SE" \
|
|
--subject="uid=kdc,DC=test,DC=h5l,DC=se" \
|
|
--certificate="FILE:kdc.pem"
|
|
@end example
|
|
|
|
The users also needs to have certificates. For your first client,
|
|
generate a certificate of type ``pkinit-client''. The client doesn't
|
|
need to have the PK-INIT SubjectAltName set; you can have the Subject
|
|
DN in the ACL file (pki-mapping) instead.
|
|
|
|
You need to change --subject and --pk-init-principal in the command
|
|
below to something appropriate for your site. You can omit
|
|
--pk-init-principal if you're going to use the ACL file instead.
|
|
|
|
@example
|
|
hxtool issue-certificate \
|
|
--ca-certificate=FILE:ca.pem \
|
|
--generate-key=rsa \
|
|
--type="pkinit-client" \
|
|
--pk-init-principal="lha@@TEST.H5L.SE" \
|
|
--subject="uid=lha,DC=test,DC=h5l,DC=se" \
|
|
--certificate="FILE:user.pem"
|
|
@end example
|
|
|
|
@subsection Validate the certificate
|
|
|
|
hxtool also contains a tool that will validate certificates according
|
|
to rules from the PKIX document. These checks are not complete, but
|
|
they provide a good test of whether you got all of the basic bits
|
|
right in your certificates.
|
|
|
|
@example
|
|
hxtool validate FILE:user.pem
|
|
@end example
|
|
|
|
@section Use OpenSSL to create certificates
|
|
|
|
This section tries to give the CA owners hints how to create
|
|
certificates using OpenSSL (or CA software based on OpenSSL).
|
|
|
|
@subsection Using OpenSSL to create certificates with krb5PrincipalName
|
|
|
|
To make OpenSSL create certificates with krb5PrincipalName, use an
|
|
@file{openssl.cnf} as described below. To see a complete example of
|
|
creating client and KDC certificates, see the test-data generation
|
|
script @file{lib/hx509/data/gen-req.sh} in the source-tree. The
|
|
certicates it creates are used to test the PK-INIT functionality in
|
|
@file{tests/kdc/check-kdc.in}.
|
|
|
|
To use this example you have to use OpenSSL 0.9.8a or later.
|
|
|
|
@example
|
|
|
|
[user_certificate]
|
|
subjectAltName=otherName:1.3.6.1.5.2.2;SEQUENCE:princ_name
|
|
|
|
[princ_name]
|
|
realm = EXP:0, GeneralString:MY.REALM
|
|
principal_name = EXP:1, SEQUENCE:principal_seq
|
|
|
|
[principal_seq]
|
|
name_type = EXP:0, INTEGER:1
|
|
name_string = EXP:1, SEQUENCE:principals
|
|
|
|
[principals]
|
|
princ1 = GeneralString:userid
|
|
|
|
@end example
|
|
|
|
Command usage:
|
|
|
|
@example
|
|
openssl x509 -extensions user_certificate
|
|
openssl ca -extensions user_certificate
|
|
@end example
|
|
|
|
|
|
@c --- ms certificate
|
|
@c
|
|
@c [ new_oids ]
|
|
@c msCertificateTemplateName = 1.3.6.1.4.1.311.20.2
|
|
@c
|
|
@c
|
|
@c [ req_smartcard ]
|
|
@c keyUsage = digitalSignature, keyEncipherment
|
|
@c extendedKeyUsage = msSmartcardLogin, clientAuth
|
|
@c msCertificateTemplateName = ASN1:BMP:SmartcardLogon
|
|
@c subjectAltName = otherName:msUPN;UTF8:lukeh@dsg.padl.com
|
|
@c #subjectAltName = email:copy
|
|
|
|
|
|
@section Using PK-INIT with Windows
|
|
|
|
@subsection Client configration
|
|
|
|
Clients using a Windows KDC with PK-INIT need configuration since
|
|
windows uses pre-standard format and this can't be autodetected.
|
|
|
|
The pkinit_win2k_require_binding option requires the reply for the KDC
|
|
to be of the new, secure, type that binds the request to
|
|
reply. Before, clients could fake the reply from the KDC. To use this
|
|
option you have to apply a fix from Microsoft.
|
|
|
|
@example
|
|
[realms]
|
|
MY.MS.REALM = @{
|
|
pkinit_win2k = yes
|
|
pkinit_win2k_require_binding = no
|
|
@}
|
|
@end example
|
|
|
|
@subsection Certificates
|
|
|
|
The client certificates need to have the extended keyusage ``Microsoft
|
|
Smartcardlogin'' (openssl has the OID shortname msSmartcardLogin).
|
|
|
|
See Microsoft Knowledge Base Article - 281245 ``Guidelines for Enabling
|
|
Smart Card Logon with Third-Party Certification Authorities'' for a
|
|
more extensive description of how set setup an external CA so that it
|
|
includes all the information required to make a Windows KDC happy.
|
|
|
|
@subsection Configure Windows 2000 CA
|
|
|
|
To enable Microsoft Smartcardlogin for certificates in your Windows
|
|
2000 CA, you want to look at Microsoft Knowledge Base Article - 313274
|
|
``HOW TO: Configure a Certification Authority to Issue Smart Card
|
|
Certificates in Windows''.
|
|
|
|
@node Debugging Kerberos problems, , Setting up PK-INIT, Setting up a realm
|
|
@section Debugging Kerberos problems
|
|
|
|
To debug Kerberos client and server problems you can enable debug
|
|
traceing by adding the following to @file{/etc/krb5,conf}. Note that the
|
|
trace logging is sparse at the moment, but will continue to improve.
|
|
|
|
@example
|
|
[logging]
|
|
libkrb5 = 0-/SYSLOG:
|
|
@end example
|
|
|
|
|
|
|
|
|