Overview

Hadoop can store large amounts of data. Therefore, Kerberos must be applied to securely protect this data.

In this post, we introduce the process of building a KDC server required for Kerberos implementation. For more details, please refer to the [ubuntu-MIT-kerberos-setting](https://ubuntu.com/server/docs/service-kerberos) documentation.

Installing krb5-kdc and krb5-admin-server

Install `krb5-kdc` and `krb5-admin-server` using the apt command.

sudo apt install krb5-kdc krb5-admin-server

During installation, a screen will appear asking you to enter a realm as shown below. Enter your desired realm at this point. I set it to `UBUNTU.YJ.COM`.

A screen will appear asking you to enter the hostname where the Kerberos server will be installed. Enter the server's hostname as shown below.

Next, enter the hostname for the admin server. In my case, since I am installing the admin server on the same server as the Kerberos server, I entered the same hostname.

Once the installation is complete, create the database using the `krb5_newrealm` command. During this process, you will set the database master password.

root@ubuntu01:~# sudo krb5_newrealm

This script should be run on the master KDC/admin server to initialize

a Kerberos realm. It will ask you to type in a master key password.

This password will be used to generate a key that is stored in

/etc/krb5kdc/stash. You should try to remember this password, but it

is much more important that it be a strong password than that it be

remembered. However, if you lose the password and /etc/krb5kdc/stash,

you cannot decrypt your Kerberos database.

Loading random data

Initializing database '/var/lib/krb5kdc/principal' for realm 'UBUNTU.YJ.COM',

master key name 'K/M@UBUNTU.YJ.COM'

You will be prompted for the database Master Password.

It is important that you NOT FORGET this password.

Enter KDC database master key:

Re-enter KDC database master key to verify:

Now that your realm is set up you may wish to create an administrative

principal using the addprinc subcommand of the kadmin.local program.

Then, this principal can be added to /etc/krb5kdc/kadm5.acl so that

you can use the kadmin program on other computers. Kerberos admin

principals usually belong to a single user and end in /admin. For

example, if jruser is a Kerberos administrator, then in addition to

the normal jruser principal, a jruser/admin principal should be

created.

Don't forget to set up DNS information so your clients can find your

KDC and admin servers. Doing so is documented in the administration

guide.

Running kadmin.local

Running the `kadmin.local` command launches a program that can manage principals belonging to the realm and KDC. Running listprinc shows the currently registered principals.

root@ubuntu01:~# kadmin.local

Authenticating as principal youngjukim/admin@UBUNTU.YJ.COM with password.

kadmin.local: listprincs

K/M@UBUNTU.YJ.COM

kadmin/admin@UBUNTU.YJ.COM

kadmin/changepw@UBUNTU.YJ.COM

krbtgt/UBUNTU.YJ.COM@UBUNTU.YJ.COM

Commands available in kadmin.local

kadmin.local: ?

Available kadmin.local requests:

add_principal, addprinc, ank

Add principal

delete_principal, delprinc

Delete principal

modify_principal, modprinc

Modify principal

rename_principal, renprinc

Rename principal

change_password, cpw Change password

get_principal, getprinc Get principal

list_principals, listprincs, get_principals, getprincs

List principals

add_policy, addpol Add policy

modify_policy, modpol Modify policy

delete_policy, delpol Delete policy

get_policy, getpol Get policy

list_policies, listpols, get_policies, getpols

List policies

get_privs, getprivs Get privileges

ktadd, xst Add entry(s) to a keytab

ktremove, ktrem Remove entry(s) from a keytab

lock Lock database exclusively (use with extreme caution!)

unlock Release exclusive database lock

purgekeys Purge previously retained old keys from a principal

get_strings, getstrs Show string attributes on a principal

set_string, setstr Set a string attribute on a principal

del_string, delstr Delete a string attribute on a principal

list_requests, lr, ? List available requests.

Registering KDC Admin ACL

If you want to register admin principals other than the youngjukim/admin principal, uncomment the `*/admin *` section as shown below. After restarting krb5-admin-server, any principal created with \*/admin will be configured to have admin privileges.

This file Is the access control list for krb5 administration.

When this file is edited run service krb5-admin-server restart to activate

One common way to set up Kerberos administration is to allow any principal

ending in /admin is given full administrative rights.

To enable this, uncomment the following line:

*/admin *

Restart krb5-admin-server to apply the admin ACL.

root@ubuntu01:~# service krb5-admin-server status

● krb5-admin-server.service - Kerberos 5 Admin Server

Loaded: loaded (/lib/systemd/system/krb5-admin-server.service; enabled; vendor preset: enabled)

Active: active (running) since Sun 2022-11-20 16:00:19 UTC; 11min ago

root@ubuntu01:~# service krb5-admin-server restart

You can change the KDC server's port, ticket lifetime, log location, database location, encryption type, and more in the file below.

[kdcdefaults]

kdc_ports = 750,88

[realms]

UBUNTU.YJ.COM = {

database_name = /var/lib/krb5kdc/principal

admin_keytab = FILE:/etc/krb5kdc/kadm5.keytab

acl_file = /etc/krb5kdc/kadm5.acl

key_stash_file = /etc/krb5kdc/stash

kdc_ports = 750,88

max_life = 10h 0m 0s

max_renewable_life = 7d 0h 0m 0s

master_key_type = des3-hmac-sha1

#supported_enctypes = aes256-cts:normal aes128-cts:normal

default_principal_flags = +preauth

}

kinit Test

For a client to access the KDC and obtain a ticket, the following must be done first. For more details, refer to (krb5-client)[https://plugins.miniorange.com/steps-to-setup-kerberos-on-ubuntu-rhel-centos].

1. The principal that wants to access the KDC must be added to the database on the KDC server side.

2. The client must have the library installed for KDC access. (krb5-user or krb5-workstation)

3. The client performs kinit principal. At this point, the client must either have the keytab for that principal or know the password.

1. Creating a principal in kadmin.local (password method)

root@ubuntu01:~# kadmin.local

Authenticating as principal youngjukim/admin@UBUNTU.YJ.COM with password.

kadmin.local: addprinc test-user

No policy specified for test-user@UBUNTU.YJ.COM; defaulting to no policy

Enter password for principal "test-user@UBUNTU.YJ.COM":

Re-enter password for principal "test-user@UBUNTU.YJ.COM":

Principal "test-user@UBUNTU.YJ.COM" created.

2. Installing the library for KDC access on the client + Modifying /etc/krb5.conf

Enter the command `sudo apt install krb5-user` to proceed with the installation.

root@ubuntu02:~# cat /etc/krb5.conf

[libdefaults]

default_realm = UBUNTU.YJ.COM

The following krb5.conf variables are only for MIT Kerberos.

kdc_timesync = 1

ccache_type = 4

forwardable = true

proxiable = true

The following encryption type specification will be used by MIT Kerberos

if uncommented. In general, the defaults in the MIT Kerberos code are

correct and overriding these specifications only serves to disable new

encryption types as they are added, creating interoperability problems.

#

The only time when you might need to uncomment these lines and change

the enctypes is if you have local software that will break on ticket

caches containing ticket encryption types it doesn't know about (such as

old versions of Sun Java).

default_tgs_enctypes = des3-hmac-sha1

default_tkt_enctypes = des3-hmac-sha1

permitted_enctypes = des3-hmac-sha1

The following libdefaults parameters are only for Heimdal Kerberos.

fcc-mit-ticketflags = true

[realms]

UBUNTU.YJ.COM = {

kdc = ubuntu01

admin_server = ubuntu01

}

[domain_realm]

3. Performing kinit principal

Perform kinit principal. If you have a keytab, you can specify the keytab path using the -kt option. Entering klist will show the information of the issued Kerberos ticket.

root@ubuntu02:~# kinit -V test-user

Using default cache: /tmp/krb5cc_0

Using principal: test-user@UBUNTU.YJ.COM

Password for test-user@UBUNTU.YJ.COM:

Authenticated to Kerberos v5

root@ubuntu02:~# klist

Ticket cache: FILE:/tmp/krb5cc_0

Default principal: test-user@UBUNTU.YJ.COM

Valid starting Expires Service principal

11/20/2022 16:34:17 11/21/2022 02:34:17 krbtgt/UBUNTU.YJ.COM@UBUNTU.YJ.COM

renew until 11/21/2022 16:33:33

Reference

- (https://ubuntu.com/server/docs/service-kerberos)[https://ubuntu.com/server/docs/service-kerberos]

- (https://web.mit.edu/kerberos/)[https://web.mit.edu/kerberos/]

- (https://web.mit.edu/kerberos/krb5-latest/doc/)[https://web.mit.edu/kerberos/krb5-latest/doc/]

Quiz

Q1: What is the main topic covered in "How to Install krb5-kdc on Ubuntu (Kerberos)"?

Learn how to install krb5-kdc on Ubuntu

Install krb5-kdc and krb5-admin-server using the apt command. During installation, a screen will

appear asking you to enter a realm as shown below. Enter your desired realm at this point. I set

it to UBUNTU.YJ.COM.

Running the kadmin.local command launches a program that can manage principals belonging to the

realm and KDC. Running listprinc shows the currently registered principals. Commands available in

kadmin.local

If you want to register admin principals other than the youngjukim/admin principal, uncomment the

/admin section as shown below. After restarting krb5-admin-server, any principal created with

\*/admin will be configured to have admin privileges.

For a client to access the KDC and obtain a ticket, the following must be done first. For more

details, refer to

(krb5-client)[https://plugins.miniorange.com/steps-to-setup-kerberos-on-ubuntu-rhel-centos].