248 lines
8.7 KiB
Plaintext
248 lines
8.7 KiB
Plaintext
@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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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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@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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@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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@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} flag to get a random password) and then
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extract it with @samp{ext_keytab}.
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@example
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kadmin> add --random 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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@section Remote administration
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The administration server, @samp{kadmind}, is started by @samp{inetd}
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and you should add a line similar to the one below to your
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@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,...]
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@end smallexample
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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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@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{kpasswd/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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@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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