@c $Id: setup.texi,v 1.27.2.2 2003/10/21 21:37:56 lha Exp $ @node Setting up a realm, Things in search for a better place, Building and Installing, Top @chapter Setting up a realm @menu * Configuration file:: * Creating the database:: * keytabs:: * Serving Kerberos 4/524/kaserver:: * Remote administration:: * Password changing:: * Testing clients and servers:: * Slave Servers:: * Incremental propagation:: * Salting:: * Cross realm:: * Transit policy:: * Setting up DNS:: @end menu A @cindex realm realm is an administrative domain. The name of a Kerberos realm is usually the Internet domain name in uppercase. Call your realm the same as your Internet domain name if you do not have strong reasons for not doing so. It will make life easier for you and everyone else. @node Configuration file, Creating the database, Setting up a realm, Setting up a realm @section Configuration file To setup a realm you will first have to create a configuration file: @file{/etc/krb5.conf}. The @file{krb5.conf} file can contain many configuration options, some of which are described here. There is a sample @file{krb5.conf} supplied with the distribution. The configuration file is a hierarchical structure consisting of sections, each containing a list of bindings (either variable assignments or subsections). A section starts with @samp{[section-name]}. A binding consists of a left hand side, an equal (@samp{=}) and a right hand side (the left hand side tag must be separated from the equal with some whitespace.) Subsections has a @samp{@{} as the first non-whitespace character after the equal. All other bindings are treated as variable assignments. The value of a variable extends to the end of the line. @example [section1] a-subsection = @{ var = value1 other-var = value with @{@} sub-sub-section = @{ var = 123 @} @} var = some other value [section2] var = yet another value @end example In this manual, names of sections and bindings will be given as strings separated by slashes (@samp{/}). The @samp{other-var} variable will thus be @samp{section1/a-subsection/other-var}. For in-depth information about the contents of the configuration file, refer to the @file{krb5.conf} manual page. Some of the more important sections are briefly described here. The @samp{libdefaults} section contains a list of library configuration parameters, such as the default realm and the timeout for KDC responses. The @samp{realms} section contains information about specific realms, such as where they hide their KDC. This section serves the same purpose as the Kerberos 4 @file{krb.conf} file, but can contain more information. Finally the @samp{domain_realm} section contains a list of mappings from domains to realms, equivalent to the Kerberos 4 @file{krb.realms} file. To continue with the realm setup, you will have to create a configuration file, with contents similar to the following. @example [libdefaults] default_realm = MY.REALM [realms] MY.REALM = @{ kdc = my.kdc my.slave.kdc kdc = my.third.kdc @} [domain_realm] .my.domain = MY.REALM @end example If you use a realm name equal to your domain name, you can omit the @samp{libdefaults}, and @samp{domain_realm}, sections. If you have a SRV-record for your realm, or your Kerberos server has CNAME called @samp{kerberos.my.realm}, you can omit the @samp{realms} section too. @node Creating the database, keytabs, Configuration file, Setting up a realm @section Creating the database The database library will look for the database in the directory @file{/var/heimdal}, so you should probably create that directory. Make sure the directory have restrictive permissions. @example # mkdir /var/heimdal @end example The keys of all the principals are stored in the database. If you choose to, these can be encrypted with a master key. You do not have to remember this key (or password), but just to enter it once and it will be stored in a file (@file{/var/heimdal/m-key}). If you want to have a master key, run @samp{kstash} to create this master key: @example # kstash Master key: Verifying password - Master key: @end example To initialise the database use the @code{kadmin} program, with the @samp{-l} option (to enable local database mode). First issue a @kbd{init MY.REALM} command. This will create the database and insert default principals for that realm. You can have more than one realm in one database, so @samp{init} does not destroy any old database. Before creating the database, @samp{init} will ask you some questions about max ticket lifetimes. After creating the database you should probably add yourself to it. You do this with the @samp{add} command. It takes as argument the name of a principal. The principal should contain a realm, so if you haven't setup a default realm, you will need to explicitly include the realm. @example # kadmin -l kadmin> init MY.REALM Realm max ticket life [unlimited]: Realm max renewable ticket life [unlimited]: kadmin> add me Max ticket life [unlimited]: Max renewable life [unlimited]: Attributes []: Password: Verifying password - Password: @end example Now start the KDC and try getting a ticket. @example # kdc & # kinit me me@@MY.REALMS's Password: # klist Credentials cache: /tmp/krb5cc_0 Principal: me@@MY.REALM Issued Expires Principal Aug 25 07:25:55 Aug 25 17:25:55 krbtgt/MY.REALM@@MY.REALM @end example If you are curious you can use the @samp{dump} command to list all the entries in the database. It should look something similar to the following example (note that the entries here are truncated for typographical reasons): @smallexample kadmin> dump me@@MY.REALM 1:0:1:0b01d3cb7c293b57:-:0:7:8aec316b9d1629e3baf8 ... kadmin/admin@@MY.REALM 1:0:1:e5c8a2675b37a443:-:0:7:cb913ebf85 ... krbtgt/MY.REALM@@MY.REALM 1:0:1:52b53b61c875ce16:-:0:7:c8943be ... kadmin/changepw@@MY.REALM 1:0:1:f48c8af2b340e9fb:-:0:7:e3e6088 ... @end smallexample @node keytabs, Serving Kerberos 4/524/kaserver, Creating the database, Setting up a realm @section keytabs To extract a service ticket from the database and put it in a keytab you need to first create the principal in the database with @samp{ank} (using the @kbd{--random-key} flag to get a random key) and then extract it with @samp{ext_keytab}. @example kadmin> add --random-key host/my.host.name Max ticket life [unlimited]: Max renewable life [unlimited]: Attributes []: kadmin> ext host/my.host.name # ktutil list Version Type Principal 1 des-cbc-md5 host/my.host.name@@MY.REALM 1 des-cbc-md4 host/my.host.name@@MY.REALM 1 des-cbc-crc host/my.host.name@@MY.REALM 1 des3-cbc-sha1 host/my.host.name@@MY.REALM @end example @node Serving Kerberos 4/524/kaserver, Remote administration, keytabs, Setting up a realm @section Serving Kerberos 4/524/kaserver Heimdal can be configured to support 524, Kerberos 4 or kaserver. All theses services are default turned off. Kerberos 4 support also depends on if Kerberos 4 support is compiled in with Heimdal. @subsection 524 524 is a service that allows the KDC to convert Kerberos 5 tickets to Kerberos 4 tickets for backward compatibility. See also Using 2b tokens with AFS in @xref{Things in search for a better place}. 524 can be turned on by adding this to the configuration file @example [kdc] enable-524 = yes @end example @subsection Kerberos 4 Kerberos 4 is the predecessor to to Kerberos 5. It only support single DES. You should only enable Kerberos 4 support if you have a need for for compatibility with an installed base of Kerberos 4 clients/servers. Kerberos 4 can be turned on by adding this to the configuration file @example [kdc] enable-kerberos4 = yes @end example @subsection kaserver Kaserver is a Kerberos 4 that is used in AFS, the protocol have some features over plain Kerberos 4, but like Kerberos 4 only use single DES too. You should only enable Kerberos 4 support if you have a need for for compatibility with an installed base of AFS machines. Kaserver can be turned on by adding this to the configuration file @example [kdc] enable-kaserver = yes @end example @node Remote administration, Password changing, Serving Kerberos 4/524/kaserver, Setting up a realm @section Remote administration The administration server, @samp{kadmind}, can be started by @samp{inetd} (which isn't recommended) or run as a normal daemon. If you want to start it from @samp{inetd} you should add a line similar to the one below to your @file{/etc/inetd.conf}. @example kerberos-adm stream tcp nowait root /usr/heimdal/libexec/kadmind kadmind @end example You might need to add @samp{kerberos-adm} to your @file{/etc/services} as 749/tcp. Access to the administration server is controlled by an acl-file, (default @file{/var/heimdal/kadmind.acl}.) The lines in the access file, has the following syntax: @smallexample principal [priv1,priv2,...] [glob-pattern] @end smallexample The matching is from top to bottom for matching principal (and if given, glob-pattern). When there is a match, the rights of that lines are used. The privileges you can assign to a principal are: @samp{add}, @samp{change-password} (or @samp{cpw} for short), @samp{delete}, @samp{get}, @samp{list}, and @samp{modify}, or the special privilege @samp{all}. All of these roughly corresponds to the different commands in @samp{kadmin}. If a @var{glob-pattern} is given on a line, it restricts the right for the principal to only apply for the subjects that match the pattern. The patters are of the same type as those used in shell globbing, see @url{none,,fnmatch(3)}. In the example below @samp{lha/admin} can change every principal in the database. @samp{jimmy/admin} can only modify principals that belong to the realm @samp{E.KTH.SE}. @samp{mille/admin} is working at the help desk, so he should only be able to change the passwords for single component principals (ordinary users). He will not be able to change any @samp{/admin} principal. @example lha/admin@@E.KTH.SE all jimmy/admin@@E.KTH.SE all *@@E.KTH.SE jimmy/admin@@E.KTH.SE all */*@@E.KTH.SE mille/admin@@E.KTH.SE change-password *@@E.KTH.SE @end example @node Password changing, Testing clients and servers, Remote administration, Setting up a realm @section Password changing To allow users to change their passwords, you should run @samp{kpasswdd}. It is not run from @samp{inetd}. You might need to add @samp{kpasswd} to your @file{/etc/services} as 464/udp. @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 (pre-authentication provides some defense against off-line attacks). To ensure that the users choose good passwords, you can enable password quality controls in @samp{kpasswdd}. The controls themselves are done in a shared library that is used by @samp{kpasswdd}. To configure in these controls, add lines similar to the following to your @file{/etc/krb5.conf}: @example [password_quality] check_library = @var{library} check_function = @var{function} @end example The function @var{function} in the shared library @var{library} will be called for proposed new passwords. The function should be declared as: @example const char * function(krb5_context context, krb5_principal principal, krb5_data *pwd); @end example The function should verify that @var{pwd} is a good password for @var{principal} and if so return @code{NULL}. If it is deemed to be of low quality, it should return a string explaining why that password should not be used. 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 the cracklib library built with the patch available at @url{ftp://ftp.pdc.kth.se/pub/krb/src/cracklib.patch}. If no password quality checking function is configured, it is only verified that it is at least six characters of length. @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 shall have the same database so that they present the same service to all the users. The @pindex hprop @code{hprop} program, running on the master, will propagate the database to the slaves, running @pindex hpropd @code{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 @code{ktutil} command and start @pindex hpropd @code{propd}, 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 on-hands 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 @code{hpropd} from @code{inetd} on the slave(s) and regularly run @pindex hprop @code{hprop} on the master to regularly propagate the database. Starting the propagation once an hour from @code{cron} is probably a good idea. @node Incremental propagation, Salting , Slave Servers, Setting up a realm @section Incremental propagation There is also a newer and still somewhat experimental 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 assigned 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 versioner than the oldest one in the log, the whole database has to be sent. Protocol-wise, all the slaves connects 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. @subsection Configuring incremental propagation The program that runs on the master is @code{ipropd-master} and all clients run @code{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 these 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 The next step is to start the @code{ipropd-master} process on the master server. The @code{ipropd-master} listens on the UNIX-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 @code{ipropd-slave} on all the slaves: @example master# /usr/heimdal/libexec/ipropd-master & slave# /usr/heimdal/libexec/ipropd-slave master & @end example @node Salting, Cross realm, Incremental propagation, Setting up a realm @section Salting @cindex Salting Salting is used to make it harder to precalculate all possible keys. Using a salt increases the search space to make it almost impossible to precalculate 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, des3, arcfour), @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 includes @itemize @bullet @item @code{v4} (or @code{des:pw-salt:}) The Kerberos 4 salting is using no salt att all. Reason there is colon that the end or 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} means all regular encryption-types that is regular @item @code{afs3-salt} @code{afs3-salt} is the salting that is used with Transarc kaserver. Its the cell appended to the password. @end itemize @node Cross realm, Transit policy , Salting, Setting up a realm @section Cross realm @cindex Cross realm Suppose you are residing 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 add a share keys between two realms that trust each other. When a client program, such as @code{telnet} or @code{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 one 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 @cartouche 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 cartouche @end example @node Transit policy, Setting up DNS , Cross realm, Setting up a realm @section Transit policy @cindex Transit policy If you want to use cross realm authentication through an intermediate realm it must be explicitly allowed by either the KDCs or the server receiving the request. This is done in @file{krb5.conf} in the @code{[capaths]} section. 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, this is since there is no way to know if know if one of the transited-realms changed the order of the list. The syntax for @code{[capaths]} section: @example @cartouche [capaths] CLIENT-REALM = @{ SERVER-REALM = PERMITTED-CROSS-REALMS ... @} @end cartouche @end example The realm @code{STACKEN.KTH.SE} allows clients from @code{SU.SE} and @code{DSV.SU.SE} to cross in. Since @code{STACKEN.KTH.SE} only have direct cross realm with @code{KTH.SE}, and @code{DSV.SU.SE} only have direct cross realm with @code{SU.SE} they need to use both @code{SU.SE} and @code{KTH.SE} as transit realms. @example @cartouche [capaths] SU.SE = @{ STACKEN.KTH.SE = KTH.SE @} DSV.SU.SE = @{ STACKEN.KTH.SE = SU.SE KTH.SE @} @end cartouche @end example @c To test the cross realm configuration, use: @c kmumble transit-check client server transit-realms ... @node Setting up DNS, , Transit policy, Setting up a realm @section Setting up DNS @cindex Setting up DNS 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 @code{SRV} resource record (RR) for the realm. If no SRV RRs are found, it will fall back to looking for a @code{A} RR for a machine named kerberos.REALM, and then kerberos-1.REALM, etc Adding this information to DNS makes the client have less configuration (in the common case, no configuration) and allows the system administrator to change the number of KDCs and on what machines they are running without caring about clients. The backside of using DNS 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. 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)).