Beyond Linux® From Scratch - Version 6.3

Chapter 4. Security

Heimdal-1.1

Introduction to Heimdal

Heimdal is a free implementation of Kerberos 5 that aims to be compatible with MIT Kerberos 5 and is backward compatible with Kerberos 4. Kerberos is a network authentication protocol. Basically it preserves the integrity of passwords in any untrusted network (like the Internet). Kerberized applications work hand-in-hand with sites that support Kerberos to ensure that passwords cannot be stolen or compromised. A Kerberos installation will make changes to the authentication mechanisms on your network and will overwrite several programs and daemons from the Shadow, Inetutils and Qpopper packages. See http://anduin.linuxfromscratch.org/files/BLFS/6.3/heimdal-overwrites for a complete list of all the files and commands to rename each of them.

Package Information

Additional Downloads

Heimdal Dependencies

Required to Build the Server-Side Tools

Berkeley DB-4.5.20 is recommended (installed in LFS) or GDBM-1.8.3

Recommended

OpenSSL-0.9.8g

Optional

Linux-PAM-0.99.10.0, OpenLDAP-2.3.39, X Window System, and libcap

[Note]

Note

Some sort of time synchronization facility on your system (like NTP-4.2.4p0) is required since Kerberos won't authenticate if the time differential between a kerberized client and the KDC server is more than 5 minutes.

User Notes: http://wiki.linuxfromscratch.org/blfs/wiki/heimdal

Installation of Heimdal

[Warning]

Warning

Ensure you really need a Kerberos installation before you decide to install this package. Failure to install and configure the package correctly can alter your system so that users cannot log in.

Install Heimdal by running the following commands: 

patch -Np1 -i ../heimdal-1.1-blfs_docs-1.patch &&
patch -Np1 -i ../heimdal-1.1-libss-1.patch &&

./configure --prefix=/usr \
            --sysconfdir=/etc/heimdal \
            --libexecdir=/usr/sbin \
            --localstatedir=/var/lib/heimdal \
            --datadir=/var/lib/heimdal \
            --with-hdbdir=/var/lib/heimdal \
            --with-readline=/usr \
            --enable-kcm &&
make

If you have teTeX-3.0 installed and wish to create alternate forms of the documentation, change into the doc directory and issue any or all of the following commands: 

pushd doc                                        &&

make html                                        &&

texi2pdf                            heimdal.texi &&
texi2dvi                            heimdal.texi &&
dvips                -o heimdal.ps  heimdal.dvi  &&
makeinfo --plaintext -o heimdal.txt heimdal.texi &&

texi2pdf                            hx509.texi   &&
texi2dvi                            hx509.texi   &&
dvips                -o hx509.ps    hx509.dvi    &&
makeinfo --plaintext -o hx509.txt   hx509.texi   &&

popd

To test the results, issue: make -k check. The ipropd test is known to fail but all others should pass.

Now, as the root user: 

make install &&

install -v -m755 -d /usr/share/doc/heimdal-1.1 &&
install -v -m644    doc/{init-creds,layman.asc} \
                    /usr/share/doc/heimdal-1.1 &&

ln -sfv         mech.5 /usr/share/man/man5/qop.5  &&
ln -sfv ../man5/mech.5 /usr/share/man/cat5/qop.5  &&
ln -sfv ../man5/mech.5 /usr/share/man/cat5        &&

mv -v /bin/login          /bin/login.SHADOW &&
mv -v /bin/su             /bin/su.SHADOW    &&
mv -v /usr/bin/{login,su} /bin              &&
ln -v -sf ../../bin/login /usr/bin          &&

for LINK in   lib{otp,kafs,krb5,hx509,asn1,roken,crypto}; do
    mv -v     /usr/lib/${LINK}.so.* /lib &&
    ln -v -sf ../../lib/$(readlink  /usr/lib/${LINK}.so) \
              /usr/lib/${LINK}.so
done &&

mv -v     /usr/lib/$(readlink /usr/lib/libdb.so) \
          /usr/lib/libdb-?.so \
          /lib &&
ln -v -sf ../../lib/$(readlink /usr/lib/libdb.so) \
          /usr/lib/libdb.so &&

ldconfig

If you built any of the alternate forms of documentation, install it using the following commands as the root user: 

install -v -m644 doc/{heimdal,hx509}.{dvi,ps,pdf,html,txt} \
                 /usr/share/doc/heimdal-1.1

If you wish to use the CrackLib-2.8.12 library to enforce strong passwords in the KDC database, issue the following commands as the root user: 

sed -e 's|/usr/pkg|/usr|' \
    -e 's|/usr/lib/cracklib_dict|/lib/cracklib/pw_dict|' \
    -e 's|/var/heimdal|/var/lib/heimdal|' \
        lib/kadm5/check-cracklib.pl \
    > /bin/krb5-check-cracklib.pl &&

chmod -v 755 /bin/krb5-check-cracklib.pl

Command Explanations

--libexecdir=/usr/sbin: This switch causes the daemon programs to be installed into /usr/sbin.

[Tip]

Tip

If you want to preserve all your existing Inetutils package daemons, install the Heimdal daemons into /usr/sbin/heimdal (or wherever you want). Since these programs will be called from (x)inetd or rc scripts, it really doesn't matter where they are installed, as long as they are correctly specified in the /etc/(x)inetd.conf file and rc scripts. If you choose something other than /usr/sbin, you may want to move some of the user programs (such as kadmin) to /usr/sbin manually so they'll be in the privileged user's default PATH.

--localstatedir=/var/lib/heimdal, --datadir=/var/lib/heimdal and --with-hdbdir=/var/lib/heimdal: These parameters are used so that the KDC database and associated files will all reside in /var/lib/heimdal.

--with-readline=/usr: This parameter must be used so that the configure script properly locates the installed Readline package.

--enable-kcm: This parameter enables building the Kerberos Credentials Manager.

ln -sfv .../mech.5 /usr/share/man/...: These commands are used to fix some broken symbolic links.

mv ... ...SHADOW, mv ... /bin and ln ... /usr/bin: The login and su programs installed by Heimdal belong in the /bin directory. The login program is symlinked because Heimdal is expecting to find it in /usr/bin. The old executables from the Shadow package are preserved before the move so that they can be restored if you experience problems logging into the system after the Heimdal package is installed and configured.

for LINK in ...; do ...; done, mv ... /lib and ln ... /usr/lib/libdb.so: The login and su programs previously moved into the /lib directory link against Heimdal libraries as well as libraries provided by the OpenSSL and Berkeley DB packages. These libraries are also moved to /lib so they are FHS compliant and also in case /usr is located on a separate partition which may not always be mounted.

Configuring Heimdal

Config Files

/etc/heimdal/*

Configuration Information

[Note]

Note

All the configuration steps shown below must be accomplished by the root user unless otherwise noted.

Master KDC Server Configuration

Many of the commands below use <replaceable> tags to identify places where you need to substitute information specific to your network. Ensure you replace everything in these tags (there will be no angle brackets when you are done) with your site-specific information.

Create the Kerberos configuration file with the following commands: 

install -v -m755 -d /etc/heimdal &&
cat > /etc/heimdal/krb5.conf << "EOF" &&
# Begin /etc/heimdal/krb5.conf

[libdefaults]
    default_realm = <EXAMPLE.COM>
    encrypt = true

[realms]
    <EXAMPLE.COM> = {
        kdc = <hostname.example.com>
        admin_server = <hostname.example.com>
        kpasswd_server = <hostname.example.com>
    }

[domain_realm]
    .<example.com> = <EXAMPLE.COM>

[logging]
    kdc = FILE:/var/log/kdc.log
    admin_server = FILE:/var/log/kadmin.log
    default = FILE:/var/log/krb.log

# End /etc/heimdal/krb5.conf
EOF
chmod -v 644 /etc/heimdal/krb5.conf

You will need to substitute your domain and proper hostname for the occurrences of the <hostname> and <EXAMPLE.COM> names.

default_realm should be the name of your domain changed to ALL CAPS. This isn't required, but both Heimdal and MIT Kerberos recommend it.

encrypt = true provides encryption of all traffic between kerberized clients and servers. It's not necessary and can be left off. If you leave it off, you can encrypt all traffic from the client to the server using a switch on the client program instead. The [realms] parameters tell the client programs where to look for the KDC authentication services. The [domain_realm] section maps a domain to a realm.

Store the master password in a key file using the following commands: 

install -v -m755 -d /var/lib/heimdal &&
kstash

Create the KDC database: 

kadmin -l

The commands below will prompt you for information about the principles. Choose the defaults for now unless you know what you are doing and need to specify different values. You can go in later and change the defaults, should you feel the need. You may use the up and down arrow keys to use the history feature of kadmin in a similar manner as the bash history feature.

At the kadmin> prompt, issue the following statement: 

init <EXAMPLE.COM>

The database must now be populated with at least one principle (user). For now, just use your regular login name or root. You may create as few, or as many principles as you wish using the following statement: 

add <loginname>

The KDC server and any machine running kerberized server daemons must have a host key installed: 

add --random-key host/<hostname.example.com>

After choosing the defaults when prompted, you will have to export the data to a keytab file: 

ext host/<hostname.example.com>

This should have created two files in /etc/heimdal: krb5.keytab (Kerberos 5) and srvtab (Kerberos 4). Both files should have 600 (root rw only) permissions. Keeping the keytab files from public access is crucial to the overall security of the Kerberos installation.

Eventually, you'll want to add server daemon principles to the database and extract them to the keytab file. You do this in the same way you created the host principles. Below is an example: 

add --random-key ftp/<hostname.example.com>

(choose the defaults) 

ext ftp/<hostname.example.com>

Exit the kadmin program (use quit or exit) and return back to the shell prompt. Start the KDC daemon manually, just to test out the installation: 

/usr/sbin/kdc &

Attempt to get a TGT (ticket granting ticket) with the following command: 

kinit <loginname>

You will be prompted for the password you created. After you get your ticket, you should list it with the following command: 

klist

Information about the ticket should be displayed on the screen.

To test the functionality of the keytab file, issue the following command: 

ktutil list

This should dump a list of the host principals, along with the encryption methods used to access the principals.

At this point, if everything has been successful so far, you can feel fairly confident in the installation, setup and configuration of your new Heimdal Kerberos 5 installation.

If you wish to use the CrackLib-2.8.12 library to enforce strong passwords in the KDC database, you must do two things. First, add the following lines to the /etc/heimdal/krb5.conf configuration file: 

[password_quality]
    policies = builtin:external-check
    external_program = /bin/krb5-check-cracklib.pl

Next you must install the Crypt::Cracklib Perl module. Download it from the CPAN site. The URL at the time of this writing is http://cpan.org/authors/id/D/DA/DANIEL/Crypt-Cracklib-1.2.tar.gz. After unpacking the tarball and changing into the newly created directory, issue the following command to add the BLFS Cracklib dictionary location to one of the source files: 

sed -i 's|pw_dict|&\n\t\t/lib/cracklib/pw_dict|' Cracklib.pm

Then use the standard perl Makefile.PL; make; make test; make install commands. Note that one test fails due to an unknown reason.

Install the /etc/rc.d/init.d/heimdal init script included in the blfs-bootscripts-20080816 package: 

make install-heimdal
Using Kerberized Client Programs

To use the kerberized client programs (telnet, ftp, rsh, rxterm, rxtelnet, rcp, xnlock), you first must get a TGT. Use the kinit program to get the ticket. After you've acquired the ticket, you can use the kerberized programs to connect to any kerberized server on the network. You will not be prompted for authentication until your ticket expires (default is one day), unless you specify a different user as a command line argument to the program.

The kerberized programs will connect to non-kerberized daemons, warning you that authentication is not encrypted.

In order to use the Heimdal X programs, you'll need to add a service port entry to the /etc/services file for the kxd server. There is no 'standardized port number' for the 'kx' service in the IANA database, so you'll have to pick an unused port number. Add an entry to the services file similar to the entry below (substitute your chosen port number for <49150>): 

kx              <49150>/tcp   # Heimdal kerberos X
kx              <49150>/udp   # Heimdal kerberos X

For additional information consult the Heimdal hint on which the above instructions are based.

Contents

Installed Programs: afslog, ftp, ftpd, gss, hprop, hpropd, hxtool, iprop-log, ipropd-master, ipropd-slave, kadmin, kadmind, kauth, kcm, kdc, kdestroy, kdigest, kf, kfd, kgetcred, kimpersonate, kinit, klist, kpasswd, kpasswdd, krb5-check-cracklib.pl, krb5-config, kstash, ktutil, kx, kxd, login, mk_cmds-krb5, otp, otpprint, pagsh, pfrom, popper, push, rcp, rsh, rshd, rxtelnet, rxterm, string2key, su, telnet, telnetd, tenletxr, verify_krb5_conf and xnlock
Installed Libraries: hdb_ldap.{so,a}, libasn1.{so,a}, libeditline.{so,a}, libgssapi.{so,a}, libhdb.{so,a}, libheimntlm.{so,a}, libhx509.{so,a}, libkadm5clnt.{so,a}, libkadm5srv.{so,a}, libkafs.{so,a}, libkdc.{so,a}, libkrb5.{so,a}, libotp.{so,a}, libroken.{so,a}, libsl.{so,a}, libss-krb5.{so,a} and windc.{so,a}
Installed Directories: /etc/heimdal, /usr/include/gssapi, /usr/include/kadm5, /usr/include/krb5, /usr/include/roken, /usr/include/ss, /usr/share/doc/heimdal-1.1 and /var/lib/heimdal

Short Descriptions

afslog

obtains AFS tokens for a number of cells.

ftp

is a kerberized FTP client.

ftpd

is a kerberized FTP daemon.

hprop

takes a principal database in a specified format and converts it into a stream of Heimdal database records.

hpropd

is a server that receives a database sent by hprop and writes it as a local database.

iprop-log

is used to maintain the iprop log file.

ipropd-master

is a daemon which runs on the master KDC server which incrementally propagates changes to the KDC database to the slave KDC servers.

ipropd-slave

is a daemon which runs on the slave KDC servers which incrementally propagates changes to the KDC database from the master KDC server.

kadmin

is a utility used to make modifications to the Kerberos database.

kadmind

is a server for administrative access to the Kerberos database.

kauth

is a symbolic link to the kinit program.

kcm

is a process based credential cache for Kerberos tickets.

kdc

is a Kerberos 5 server.

kdestroy

removes a principle's current set of tickets.

kf

is a program which forwards tickets to a remote host through an authenticated and encrypted stream.

kfd

is a server used to receive forwarded tickets.

kgetcred

obtains a ticket for a service.

kinit

is used to authenticate to the Kerberos server as a principal and acquire a ticket granting ticket that can later be used to obtain tickets for other services.

klist

reads and displays the current tickets in the credential cache.

kpasswd

is a program for changing Kerberos 5 passwords.

kpasswdd

is a Kerberos 5 password changing server.

krb5-config

gives information on how to link programs against Heimdal libraries.

kstash

stores the KDC master password in a file.

ktutil

is a program for managing Kerberos keytabs.

kx

is a program which securely forwards X connections.

kxd

is the daemon for kx.

login

is a kerberized login program.

otp

manages one-time passwords.

otpprint

prints lists of one-time passwords.

pfrom

is a script that runs push --from.

popper

is a kerberized POP-3 server.

push

is a kerberized POP mail retrieval client.

rcp

is a kerberized rcp client program.

rsh

is a kerberized rsh client program.

rshd

is a kerberized rsh server.

rxtelnet

starts a secure xterm window with a telnet to a given host and forwards X connections.

rxterm

starts a secure remote xterm.

string2key

maps a password into a key.

su

is a kerberized su client program.

telnet

is a kerberized telnet client program.

telnetd

is a kerberized telnet server.

tenletxr

forwards X connections backwards.

verify_krb5_conf

checks krb5.conf file for obvious errors.

xnlock

is a program that acts as a secure screen saver for workstations running X.

libasn1.{so,a}

provides the ASN.1 and DER functions to encode and decode the Kerberos TGTs.

libeditline.a

is a command-line editing library with history.

libgssapi.{so,a}

contain the Generic Security Service Application Programming Interface (GSSAPI) functions which provides security services to callers in a generic fashion, supportable with a range of underlying mechanisms and technologies and hence allowing source-level portability of applications to different environments.

libhdb.{so,a}

is a Heimdal Kerberos 5 authentication/authorization database access library.

libkadm5clnt.{so,a}

contains the administrative authentication and password checking functions required by Kerberos 5 client-side programs.

libkadm5srv.{so,a}

contain the administrative authentication and password checking functions required by Kerberos 5 servers.

libkafs.{so,a}

contains the functions required to authenticated to AFS.

libkrb5.{so,a}

is an all-purpose Kerberos 5 library.

libotp.{so,a}

contains the functions required to handle authenticating one time passwords.

libroken.{so,a}

is a library containing Kerberos 5 compatibility functions.

Last updated on 2008-05-09 08:00:42 -0500