450 lines
16 KiB
Plaintext
450 lines
16 KiB
Plaintext
@c $Id: setup.texi,v 1.25 2001/08/24 05:24:33 assar Exp $
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@node Setting up a realm, Things in search for a better place, Building and Installing, Top
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@chapter Setting up a realm
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@menu
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* Configuration file::
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* Creating the database::
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* keytabs::
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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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* Salting::
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@end menu
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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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@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{[section-name]}. A binding consists of a left hand side, an equal
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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 with some whitespace.) Subsections has a
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@samp{@{} as the first non-whitespace character after the equal. 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 config 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 config 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
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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
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SRV-record for your realm, or your kerberos server has CNAME called
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@samp{kerberos.my.realm}, you can omit the @samp{realms} section too.
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@node Creating the database, keytabs, 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 @file{/var/heimdal},
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so you should probably create that directory.
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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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To initialise the database use the @code{kadmin} program, with the
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@samp{-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 max 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 setup
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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 keytabs, Remote administration, Creating the database, 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{ank}
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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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# 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 Remote administration, Password changing, keytabs, Setting up a realm
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@section Remote administration
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The administration server, @samp{kadmind}, can be started by
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@samp{inetd} (which isn't recommended) or run as a normal daemon. If you
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want to start it from @samp{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 749/tcp.
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Access to the admin server is controlled by an acl-file, (default
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@file{/var/heimdal/kadmind.acl}.) The lines in the access file, has the
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following 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 principal (and if given,
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glob-pattern). When there is a match, the rights of that lines are
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used.
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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 corresponds to the different commands
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in @samp{kadmin}.
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If a @var{glob-pattern} is given on a line, it restricts the right for
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the principal to only apply for the subjects that match the pattern.
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The patters are of the same type as those used in shell globbing, see
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@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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helpdesk, 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 @samp{kpasswdd}.
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It is not run from @samp{inetd}.
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You might need to add @samp{kpasswd} to your @file{/etc/services} as
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464/udp.
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@subsection Password quality assurance
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It is important that users have good passwords, both to make it harder
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to guess them and to avoid off-line attacks (pre-authentication provides
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some defense against off-line attacks). To ensure that the users choose
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good passwords, you can enable password quality controls in
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@samp{kpasswdd}. The controls themselves are done in a shared library
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that is used by @samp{kpasswdd}. To configure in these controls, add
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lines similar to the following to your @file{/etc/krb5.conf}:
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@example
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[password_quality]
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check_library = @var{library}
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check_function = @var{function}
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@end example
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The function @var{function} in the shared library @var{library} will be
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called for proposed new passwords. The function should be declared as:
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@example
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const char *
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function(krb5_context context, krb5_principal principal, krb5_data *pwd);
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@end example
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The function should verify that @var{pwd} is a good password for
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@var{principal} and if so return @code{NULL}. If it is deemed to be of
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low quality, it should return a string explaining why that password
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should not be used.
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Code for a password quality checking function that uses the cracklib
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library can be found in @file{lib/kadm5/sample_password_check.c} in the
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source code distribution. It requires the cracklib library built with
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the patch available at
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@url{ftp://ftp.pdc.kth.se/pub/krb/src/cracklib.patch}.
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If no password quality checking function is configured, it is only
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verified that it is at least six characters of length.
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@node Testing clients and servers, Slave Servers, Password changing, Setting up a realm
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@section Testing clients and servers
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Now you should be able to run all the clients and servers. Refer to the
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appropriate man pages for information on how to use them.
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@node Slave Servers, Incremental propagation, Testing clients and servers, Setting up a realm
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@section Slave servers, Incremental propagation, Testing clients and servers, Setting up a realm
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It is desirable to have at least one backup (slave) server in case the
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master server fails. It is possible to have any number of such slave
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servers but more than three usually doesn't buy much more redundancy.
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All Kerberos servers for a realm shall have the same database so that
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they present the same service to all the users. The
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@pindex hprop
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@code{hprop} program, running on the master, will propagate the database
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to the slaves, running
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@pindex hpropd
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@code{hpropd} processes.
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Every slave needs a keytab with a principal,
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@samp{hprop/@var{hostname}}. Add that with the
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@pindex ktutil
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@code{ktutil} command and start
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@pindex hpropd
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@code{propd}, as follows:
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@example
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slave# ktutil get -p foo/admin host/`hostname`
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slave# hpropd
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@end example
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The master will use the principal @samp{kadmin/hprop} to authenticate to
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the slaves. This principal should be added when running @kbd{kadmin -l
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init} but if you do not have it in your database for whatever reason,
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please add it with @kbd{kadmin -l add}.
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Then run
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@pindex hprop
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@code{hprop} on the master:
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@example
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master# hprop slave
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@end example
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This was just an on-hands example to make sure that everything was
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working properly. Doing it manually is of course the wrong way and to
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automate this you will want to start
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@pindex hpropd
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@code{hpropd} from @code{inetd} on the slave(s) and regularly run
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@pindex hprop
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@code{hprop} on the master to regularly propagate the database.
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Starting the propagation once an hour from @code{cron} is probably a
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good idea.
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@node Incremental propagation, Salting , Slave Servers, Setting up a realm
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@section Incremental propagation
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There is also a newer and still somewhat experimental mechanism for
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doing incremental propagation in Heimdal. Instead of sending the whole
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database regularly, it sends the changes as they happen on the master to
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the slaves. The master keeps track of all the changes by assigned a
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version number to every change to the database. The slaves know which
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was the latest version they saw and in this way it can be determined if
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they are in sync or not. A log of all the changes is kept on the master
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and when a slave is at an older versioner than the oldest one in the
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log, the whole database has to be sent.
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Protocol-wise, all the slaves connects to the master and as a greeting
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tell it the latest version that they have (@samp{IHAVE} message). The
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master then responds by sending all the changes between that version and
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the current version at the master (a series of @samp{FORYOU} messages)
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or the whole database in a @samp{TELLYOUEVERYTHING} message.
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@subsection Configuring incremental propagation
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The program that runs on the master is @code{ipropd-master} and all
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clients run @code{ipropd-slave}.
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Create the file @file{/var/heimdal/slaves} on the master containing all
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the slaves that the database should be propagated to. Each line contains
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the full name of the principal (for example
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@samp{iprop/hemligare.foo.se@@FOO.SE}).
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You should already have @samp{iprop/tcp} defined as 2121, in your
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@file{/etc/services}. Otherwise, or if you need to use a different port
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for some peculiar reason, you can use the @kbd{--port} option. This is
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useful when you have multiple realms to distribute from one server.
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Then you need to create these principals that you added in the
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configuration file. Create one @samp{iprop/hostname} for the master and
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for every slave.
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@example
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master# /usr/heimdal/sbin/ktutil get iprop/`hostname`
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@end example
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The next step is to start the @code{ipropd-master} process on the master
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server. The @code{ipropd-master} listens on the UNIX-socket
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@file{/var/heimdal/signal} to know when changes have been made to the
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database so they can be propagated to the slaves. There is also a
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safety feature of testing the version number regularly (every 30
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seconds) to see if it has been modified by some means that do not raise
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this signal. Then, start @code{ipropd-slave} on all the slaves:
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@example
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master# /usr/heimdal/libexec/ipropd-master &
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slave# /usr/heimdal/libexec/ipropd-slave master &
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@end example
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@node Salting, , Incremental propagation, Setting up a realm
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@section Salting
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@cindex Salting
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Salting is used to make it harder to precalculate all possible
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keys. Using a salt increases the search space to make it almost
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impossible to precalculate all keys. Salting is the process of mixing a
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public string (the salt) with the password, then sending it through an
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encryption-type specific string-to-key function that will output the
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fixed size encryption key.
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In Kerberos 5 the salt is determined by the encryption-type, except
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in some special cases.
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In @code{des} there is the Kerberos 4 salt
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(none at all) or the afs-salt (using the cell (realm in
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afs-lingo)).
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In @code{arcfour} (the encryption type that Microsoft Windows 2000 uses)
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there is no salt. This is to be compatible with NTLM keys in Windows
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NT 4.
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@code{[kadmin]default_keys} in @file{krb5.conf} controls
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what salting to use,
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The syntax of @code{[kadmin]default_keys} is
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@samp{[etype:]salt-type[:salt-string]}. @samp{etype} is the encryption
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type (des, des3, arcfour), @code{salt-type} is the type of salt (pw-salt
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or afs3-salt), and the salt-string is the string that will be used as
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salt (remember that if the salt is appened/prepended, the empty salt ""
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is the same thing as no salt at all).
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Common types of salting includes
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@itemize @bullet
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@item @code{v4} (or @code{des:pw-salt:})
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The Kerberos 4 salting is using no salt att all. Reson there is colon
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that the end is that
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@item @code{v5} (or @code{pw-salt})
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@code{pw-salt} means all regular encryption-types that is regular
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@item @code{afs3-salt}
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@code{afs3-salt} is the salting that is used with Transarc kaserver. Its
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the cell appended to the password.
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@end itemize
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