MIT krb5-1.4

Introduction to MIT krb5

MIT krb5 is a free implementation of Kerberos 5. Kerberos is a network authentication protocol. It centralizes the authentication database and uses kerberized applications to work with servers or services that support Kerberos allowing single logins and encrypted communication over internal networks or the Internet.

Package information

Download (HTTP): http://web.mit.edu/kerberos/www/dist/krb5/1.4/krb5-1.4-signed.tar
Download (FTP):
Download MD5 sum: 2fa56607677544e3a27b42f7cfa1155b
Download size: 6.6 MB
Estimated disk space required: 55 MB
Estimated build time: 2.55 SBU

MIT krb5 dependencies

Optional

xinetd-2.3.13 (services servers only), Linux-PAM-0.78 (for xdm based logins) and OpenLDAP-2.2.20 (alternative for krb5kdc password database)

Note

Some sort of time synchronization facility on your system (like NTP-4.2.0) is required since Kerberos won't authenticate if there is a time difference between a kerberized client and the KDC server.

Installation of MIT krb5

MIT krb5 is distributed in a TAR file containing a compressed TAR package and a detached PGP ASC file.

If you have installed GnuPG-1.4.0, you can authenticate the package with the following command:

gpg --verify krb5-1.4.tar.gz.asc

Build MIT krb5 by running the following commands:

cd src &&
./configure --prefix=/usr --sysconfdir=/etc \
    --localstatedir=/var/lib --enable-dns \
    --enable-static --mandir=/usr/share/man &&
make

Install MIT krb5 by running the following commands as root:

make install &&
mv /bin/login /bin/login.shadow &&
cp /usr/sbin/login.krb5 /bin/login &&
mv /usr/bin/ksu /bin &&
mv /usr/lib/libkrb5.so.3* /lib &&
mv /usr/lib/libkrb4.so.2* /lib &&
mv /usr/lib/libdes425.so.3* /lib &&
mv /usr/lib/libk5crypto.so.3* /lib &&
mv /usr/lib/libcom_err.so.3* /lib &&
ln -sf ../../lib/libkrb5.so.3 /usr/lib/libkrb5.so &&
ln -sf ../../lib/libkrb4.so.2 /usr/lib/libkrb4.so &&
ln -sf ../../lib/libdes425.so.3 /usr/lib/libdes425.so &&
ln -sf ../../lib/libk5crypto.so.3 /usr/lib/libk5crypto.so &&
ln -sf ../../lib/libcom_err.so.3 /usr/lib/libcom_err.so &&
ldconfig

Command explanations

--enable-dns: This switch allows realms to be resolved using the DNS server.

--enable-static: This switch builds static libraries in addition to the shared libraries.

mv /bin/login /bin/login.shadow
cp /usr/sbin/login.krb5 /bin/login
mv /usr/bin/ksu /bin

Preserves Shadow's login command, moves ksu and login to the /bin directory.

mv /usr/lib/libkrb5.so.3* /lib
mv /usr/lib/libkrb4.so.2* /lib
mv /usr/lib/libdes425.so.3* /lib
mv /usr/lib/libk5crypto.so.3* /lib
mv /usr/lib/libcom_err.so.3* /lib
ln -sf ../../lib/libkrb5.so.3 /usr/lib/libkrb5.so
ln -sf ../../lib/libkrb4.so.2 /usr/lib/libkrb4.so
ln -sf ../../lib/libdes425.so.3 /usr/lib/libdes425.so
ln -sf ../../lib/libk5crypto.so.3 /usr/lib/libk5crypto.so
ln -sf ../../lib/libcom_err.so.3 /usr/lib/libcom_err.so

The login and ksu programs are linked against these libraries, therefore we move these libraries to /lib to allow logins without mounting /usr.

Configuring MIT krb5

Config files

/etc/krb5.conf and /var/lib/krb5kdc/kdc.conf

Configuration Information

Kerberos Configuration

Create the Kerberos configuration file with the following command:

cat > /etc/krb5.conf << "EOF"
# Begin /etc/krb5.conf

[libdefaults]
    default_realm = [LFS.ORG]
    encrypt = true

[realms]
    [LFS.ORG] = {
        kdc = [belgarath.lfs.org]
        admin_server = [belgarath.lfs.org]
    }

[domain_realm]
    .[lfs.org] = [LFS.ORG]

[logging]
    kdc = SYSLOG[:INFO[:AUTH]]
    admin_server = SYSLOG[INFO[:AUTH]]
    default = SYSLOG[[:SYS]]

# End /etc/krb5.conf
EOF

You will need to substitute your domain and proper hostname for the occurances of the [belgarath] and [lfs.org] names.

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

Create the KDC database:

kdb5_util create -r [LFS.ORG] -s

Now you should populate the database with principles (users). For now, just use your regular login name or root.

kadmin.local
kadmin:addprinc [loginname]

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

kadmin:addprinc -randkey host/[belgarath.lfs.org]

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

kadmin:ktadd host/[belgarath.lfs.org]

This should have created a file in /etc named krb5.keytab (Kerberos 5). This file 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:

kadmin:addprinc -randkey ftp/[belgarath.lfs.org]
kadmin:ktadd ftp/[belgarath.lfs.org]

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/krb5kdc &

Attempt to get a ticket with the following command:

kinit [loginname]

You will be prompted for the password you created. After you get your ticket, you can 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
ktutil:rkt /etc/krb5.keytab
ktutil:l

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

At this point, if everything has been successful so far, you can feel fairly confident in the installation and configuration of the package.

Install the /etc/rc.d/init.d/kerberos init script included in the blfs-bootscripts-6.0 package.

make install-kerberos

Using Kerberized Client Programs

To use the kerberized client programs (telnet, ftp, rsh, rcp, rlogin), you first must get an authentication ticket. 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.

Using Kerberized Server Programs

Using kerberized server programs (telnetd, kpropd, klogind and kshd) requires two additional configuration steps. First the /etc/services file must be updated to include eklogin and krb5_prop. Second, the inetd.conf or xinetd.conf must be modified for each server that will be activated, usually replacing the server from Inetutils-1.4.2.

Additional Information

For additional information consult Documentation for krb-1.4 on which the above instructions are based.

Installed Programs: compile-et, ftp, ftpd, gss-client, gss-server, k5srvutil, kadmin, kadmin.local, kadmind, kadmind4, kdb5_util, kdestroy, kinit, klist, klogind, kpasswd, kprop, kpropd, krb5-send-pr, krb5-config, krb524d, krb524init, krb5kdc, kshd, ksu, ktutil, kvno, login.krb5, rcp, rlogin, rsh, sclient, sim_client, sim_server, sserver, telnet, telnetd, uuclient, uuserver, v5passwd, v5passwdd

Installed Libraries: libcom_err.[so,a], libdes425.[so,a], libgssapi.[so,a], libgssrpc.[so,a], libkadm5clnt.[so,a], libkadm5srv.[so,a], libkdb5.[so,a], libkrb5.[so,a], libkrb4.[so,a]

Installed Directories: /usr/include/kerberosIV and /var/lib/krb5kdc

Short Descriptions

compile_et: converts the table listing error-code names into a C source file..
ftp: is a kerberized FTP client.
ftpd: is a kerberized FTP daemon.
k5srvutil: is a host keytable manipulation utility.
kadmin: is an utility used to make modifications to the Kerberos database.
kadmind: is a server for administrative access to a Kerberos database.
kdb5_util: is the KDC database utility.
kdestroy: removes the current set of tickets.
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.
klogind: is the server that responds to rlogin requests.
kpasswd: is a program for changing Kerberos 5 passwords.
kprop: takes a principal database in a specified format and converts it into a stream of database records.
kpropd: receives a database sent by kprop and writes it as a local database.
krb5-config: gives information on how to link programs against libraries.
krb5kdc: is a Kerberos 5 server.
kshd: is the server that responds to rsh requests.
ksu: is the super user program using Kerberos protocol. Requires a properly configured /etc/shells and ~/.k5login containing principals authorized to become super users.
ktutil: is a program for managing Kerberos keytabs.
kvno: prints keyversion numbers of Kerberos principals.
login.krb5: is a kerberized login program.
rcp: is a kerberized rcp client program.
rlogin: is a kerberized rlogin client program.
rsh: is a kerberized rsh client program.
telnet: is a kerberized telnet client program.
telnetd: is a kerberized telnet server.
libcom_err.[so,a]: implements the Kerberos library error code.
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.
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.
libkdb5.[so,a]: is a Kerberos 5 authentication/authorization database access library.
libkrb5.[so,a]: is an all-purpose Kerberos 5 library.

Beyond Linux From Scratch - Version 6.0

Chapter 4. Security