---
# System prepended metadata

title: 3 Installation d’un serveur Kerberos

---

# 3 Installation d’un serveur Kerberos

```shell
epsi2@ubuntu:~$ hostname -f
ubuntu
epsi2@ubuntu:~$ hostname ubuntu.epsi.fr
hostname: you must be root to change the host name
epsi2@ubuntu:~$ sudo su
[sudo] password for epsi2: 
root@ubuntu:/home/epsi2# hostname ubuntu.epsi.fr
root@ubuntu:/home/epsi2# hostname -f
ubuntu.epsi.fr
root@ubuntu:/home/epsi2# ping ubuntu.epsi.fr
PING ubuntu.epsi.fr (172.16.59.131) 56(84) bytes of data.
64 bytes from ubuntu.epsi.fr (172.16.59.131): icmp_seq=1 ttl=64 time=0.022 ms
64 bytes from ubuntu.epsi.fr (172.16.59.131): icmp_seq=2 ttl=64 time=0.032 ms
^C
--- ubuntu.epsi.fr ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.022/0.027/0.032/0.005 ms
```
## 3.1 Les paquets Debian

```shell
root@ubuntu:/home/epsi2# apt install krb5-kdc krb5-admin-server krb5-config
```


![kerberos1](https://i.imgur.com/zvv2VdU.png)

![kerberos2](https://i.imgur.com/mxcvWJq.png)

![kerberos3](https://i.imgur.com/ewJLIDE.png)

```shell
root@ubuntu:/home/epsi2# 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 'EPSI.FR',
master key name 'K/M@EPSI.FR'
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.
```



## 3.2 Configuration du serveur Kerberos

```shell
root@ubuntu:/home/epsi2# vi /etc/krb5kdc/kadm5.acl 
```

```
# 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 *
```



```shell
root@ubuntu:/home/epsi2# systemctl status krb5-kdc.service
● krb5-kdc.service - Kerberos 5 Key Distribution Center
     Loaded: loaded (/lib/systemd/system/krb5-kdc.service; enabled; vendor p>
     Active: active (running) since Fri 2021-04-30 05:31:41 PDT; 5min ago
    Process: 42770 ExecStart=/usr/sbin/krb5kdc -P /var/run/krb5-kdc.pid $DAE>
   Main PID: 42771 (krb5kdc)
      Tasks: 1 (limit: 4618)
     Memory: 1.6M
     CGroup: /system.slice/krb5-kdc.service
             └─42771 /usr/sbin/krb5kdc -P /var/run/krb5-kdc.pid

avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: Setting pktinfo on socket 0>
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: Setting up UDP socket for a>
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: setsockopt(12,IPV6_V6ONLY,1>
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: Setting pktinfo on socket :>
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: Setting up TCP socket for a>
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: Setting up TCP socket for a>
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: setsockopt(14,IPV6_V6ONLY,1>
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42770]: set up 6 sockets
avril 30 05:31:41 ubuntu.epsi.fr krb5kdc[42771]: commencing operation
avril 30 05:31:41 ubuntu.epsi.fr systemd[1]: Started Kerberos 5 Key Distribu>
lines 1-20/20 (END)
```

```shell
root@ubuntu:/home/epsi2# cat /etc/krb5.conf 

[libdefaults]
	default_realm = EPSI.FR

# 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]
	EPSI.FR = {
		kdc = ubuntu.epsi.fr
		admin_server = ubuntu.epsi.fr
	}
	ATHENA.MIT.EDU = {
		kdc = kerberos.mit.edu
		kdc = kerberos-1.mit.edu
		kdc = kerberos-2.mit.edu:88
		admin_server = kerberos.mit.edu
		default_domain = mit.edu
	}
	ZONE.MIT.EDU = {
		kdc = casio.mit.edu
		kdc = seiko.mit.edu
		admin_server = casio.mit.edu
	}
	CSAIL.MIT.EDU = {
		admin_server = kerberos.csail.mit.edu
		default_domain = csail.mit.edu
	}
	IHTFP.ORG = {
		kdc = kerberos.ihtfp.org
		admin_server = kerberos.ihtfp.org
	}
	1TS.ORG = {
		kdc = kerberos.1ts.org
		admin_server = kerberos.1ts.org
	}
	ANDREW.CMU.EDU = {
		admin_server = kerberos.andrew.cmu.edu
		default_domain = andrew.cmu.edu
	}
        CS.CMU.EDU = {
                kdc = kerberos-1.srv.cs.cmu.edu
                kdc = kerberos-2.srv.cs.cmu.edu
                kdc = kerberos-3.srv.cs.cmu.edu
                admin_server = kerberos.cs.cmu.edu
        }
	DEMENTIA.ORG = {
		kdc = kerberos.dementix.org
		kdc = kerberos2.dementix.org
		admin_server = kerberos.dementix.org
	}
	stanford.edu = {
		kdc = krb5auth1.stanford.edu
		kdc = krb5auth2.stanford.edu
		kdc = krb5auth3.stanford.edu
		master_kdc = krb5auth1.stanford.edu
		admin_server = krb5-admin.stanford.edu
		default_domain = stanford.edu
	}
        UTORONTO.CA = {
                kdc = kerberos1.utoronto.ca
                kdc = kerberos2.utoronto.ca
                kdc = kerberos3.utoronto.ca
                admin_server = kerberos1.utoronto.ca
                default_domain = utoronto.ca
	}

[domain_realm]
	.mit.edu = ATHENA.MIT.EDU
	mit.edu = ATHENA.MIT.EDU
	.media.mit.edu = MEDIA-LAB.MIT.EDU
	media.mit.edu = MEDIA-LAB.MIT.EDU
	.csail.mit.edu = CSAIL.MIT.EDU
	csail.mit.edu = CSAIL.MIT.EDU
	.whoi.edu = ATHENA.MIT.EDU
	whoi.edu = ATHENA.MIT.EDU
	.stanford.edu = stanford.edu
	.slac.stanford.edu = SLAC.STANFORD.EDU
        .toronto.edu = UTORONTO.CA
        .utoronto.ca = UTORONTO.CA
```

## 3.3 Création des comptes utilisateurs

``` shell
root@ubuntu:/home/epsi2# apt install krb5-user
```

```shell
root@ubuntu:/home/epsi2# kadmin.local
Authenticating as principal root/admin@EPSI.FR with password.
```

```shell
kadmin.local:  addprinc root/admin
WARNING: no policy specified for root/admin@EPSI.FR; defaulting to no policy
Enter password for principal "root/admin@EPSI.FR": 
Re-enter password for principal "root/admin@EPSI.FR": 
Principal "root/admin@EPSI.FR" created.
```

```shell
kadmin.local:  addprinc pafpsdnc
WARNING: no policy specified for pafpsdnc@EPSI.FR; defaulting to no policy
Enter password for principal "pafpsdnc@EPSI.FR": 
Re-enter password for principal "pafpsdnc@EPSI.FR": 
Principal "pafpsdnc@EPSI.FR" created.
```

```shell
kadmin.local:  ktadd -norandkey pafpsdnc
Entry for principal pafpsdnc with kvno 1, encryption type aes256-cts-hmac-sha1-96 added to keytab FILE:/etc/krb5.keytab.
Entry for principal pafpsdnc with kvno 1, encryption type aes128-cts-hmac-sha1-96 added to keytab FILE:/etc/krb5.keytab.
```

## 3.4 Test de bon fonctionnement

```shell
kadmin.local:  list_principals
K/M@EPSI.FR
kadmin/admin@EPSI.FR
kadmin/changepw@EPSI.FR
kadmin/ubuntu.epsi.fr@EPSI.FR
kiprop/ubuntu.epsi.fr@EPSI.FR
krbtgt/EPSI.FR@EPSI.FR
pafpsdnc@EPSI.FR
root/admin@EPSI.FR
```

```shell
root@ubuntu:/home/epsi2# kinit pafpsdnc@EPSI.FR
Password for pafpsdnc@EPSI.FR:
```

```shell
root@ubuntu:/home/epsi2# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: pafpsdnc@EPSI.FR

Valid starting       Expires              Service principal
30/04/2021 05:57:15  30/04/2021 15:57:15  krbtgt/EPSI.FR@EPSI.FR
	renew until 01/05/2021 05:57:11
```

```shell
root@ubuntu:/home/epsi2# kadmin
Authenticating as principal pafpsdnc/admin@EPSI.FR with password.
kadmin: Client 'pafpsdnc/admin@EPSI.FR' not found in Kerberos database while initializing kadmin interface
```
`kadmin` ne fonctionne pas car on essaye d'utiliser l'utilisateur `pafpsdnc` car nous venons de faire un `kinit` avec celui-ci juste avant. Mais celui-ci n'est pas administrateur (pafpsdnc/admin n'existe pas mais pafpsdnc existe !) d'où l'erreur.

```shell
root@ubuntu:/home/epsi2# kadmin.local
Authenticating as principal pafpsdnc/admin@EPSI.FR with password.
kadmin.local:
```
Kadmin.local n'utilise pas l'authentification Kerberos et n'utilise donc pas la configuration limitant la connexion aux utilisateurs contenant "/admin" présente dans le fichier : /etc/krb5kdc/kadm5.acl.

```shell
root@ubuntu:/home/epsi2# kdestroy -p pafpsdnc
root@ubuntu:/home/epsi2# klist
klist: No credentials cache found (filename: /tmp/krb5cc_0)
```

```shell
root@ubuntu:/home/epsi2# kadmin
Authenticating as principal root/admin@EPSI.FR with password.
Password for root/admin@EPSI.FR: 
kadmin:  
```
Ayant supprimé le ticket de l'utilisateur `pafpsdnc` avec `kdestroy`, `kadmin` utilise à nouveau `root/admin` qui lui existe bien.

```shell
root@ubuntu:/home/epsi2# ktutil
ktutil:  addent -password -p pafpsdnc@EPSI.FR -k 1 -e aes256-cts
Password for pafpsdnc@EPSI.FR: 
ktutil:  wkt pafpsdnc.keytab
ktutil:  quit

root@ubuntu:/home/epsi2# kinit pafpsdnc@EPSI.FR -k -t pafpsdnc.keytab
```

```shell
root@ubuntu:/home/epsi2# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: pafpsdnc@EPSI.FR

Valid starting       Expires              Service principal
30/04/2021 06:10:01  30/04/2021 16:10:01  krbtgt/EPSI.FR@EPSI.FR
	renew until 01/05/2021 06:10:01
```

```shell
root@ubuntu:/home/epsi2# klist -k pafpsdnc.keytab 
Keytab name: FILE:pafpsdnc.keytab
KVNO Principal
---- --------------------------------------------------------------------------
   1 pafpsdnc@EPSI.FR
   
root@ubuntu:/home/epsi2# klist -k /etc/krb5.keytab 
Keytab name: FILE:/etc/krb5.keytab
KVNO Principal
---- --------------------------------------------------------------------------
   1 pafpsdnc@EPSI.FR
   1 pafpsdnc@EPSI.FR
```

```shell
root@ubuntu:/home/epsi2# kdestroy -p pafpsdnc
root@ubuntu:/home/epsi2# klist
klist: No credentials cache found (filename: /tmp/krb5cc_0)
```

```shell
root@ubuntu:/home/epsi2# kpasswd pafpsdnc
Password for pafpsdnc@EPSI.FR: 
Enter new password: 
Enter it again: 
Password changed.
```

```shell
root@ubuntu:/home/epsi2# kinit pafpsdnc -k -t pafpsdnc.keytab
kinit: Preauthentication failed while getting initial credentials
```
Ayant changé le mot de passe de l'utilisateur `pafpsdnc`, la clé généré auparavant dans `pafpsdnc.keytab` n'est plus effective, il faut la regérnérer avec ktadd

```shell
root@ubuntu:/home/epsi2# kadmin.local
Authenticating as principal root/admin@EPSI.FR with password.
kadmin.local:  ktadd -norandkey pafpsdnc
Entry for principal pafpsdnc with kvno 2, encryption type aes256-cts-hmac-sha1-96 added to keytab FILE:/etc/krb5.keytab.
Entry for principal pafpsdnc with kvno 2, encryption type aes128-cts-hmac-sha1-96 added to keytab FILE:/etc/krb5.keytab.
```

```shell
root@ubuntu:/home/epsi2# klist -k /etc/krb5.keytab 
Keytab name: FILE:/etc/krb5.keytab
KVNO Principal
---- --------------------------------------------------------------------------
   1 pafpsdnc@EPSI.FR
   1 pafpsdnc@EPSI.FR
   2 pafpsdnc@EPSI.FR
   2 pafpsdnc@EPSI.FR
```

```shell
root@ubuntu:/home/epsi2# kinit pafpsdnc -k -t pafpsdnc.keytab
```

```shell
root@ubuntu:/home/epsi2# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: pafpsdnc@EPSI.FR

Valid starting       Expires              Service principal
30/04/2021 07:08:36  30/04/2021 17:08:36  krbtgt/EPSI.FR@EPSI.FR
	renew until 01/05/2021 07:08:36
```

On peut déduire de ces étapes que l'on peut, avec kerberos, modifier les clés d'authentification sans avoir besoin de renseigner le nouveau mot de passe de l'utilisateur.
Ce protocole éloigne les mots de passe des réseaux non sécurisés à tout moment, même pendant la vérification de l'utilisateur.
Pendant tout le processus de vérification, un mot de passe en texte brut n'atteint jamais le KDC ou le serveur de service.

# 4 Installation du serveur Apache

## 4.1 Installation des paquets

```shell
epsi3@ubuntu:~$ sudo apt install apache2
```

```shell
epsi3@ubuntu:~$ cat /etc/apache2/sites-enabled/000-default.conf
<VirtualHost *:80>
	# The ServerName directive sets the request scheme, hostname and port that
	# the server uses to identify itself. This is used when creating
	# redirection URLs. In the context of virtual hosts, the ServerName
	# specifies what hostname must appear in the request's Host: header to
	# match this virtual host. For the default virtual host (this file) this
	# value is not decisive as it is used as a last resort host regardless.
	# However, you must set it for any further virtual host explicitly.
	#ServerName www.example.com

	ServerAdmin webmaster@localhost
	DocumentRoot /var/www/html

	# Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
	# error, crit, alert, emerg.
	# It is also possible to configure the loglevel for particular
	# modules, e.g.
	#LogLevel info ssl:warn

	ErrorLog ${APACHE_LOG_DIR}/error.log
	CustomLog ${APACHE_LOG_DIR}/access.log combined

	# For most configuration files from conf-available/, which are
	# enabled or disabled at a global level, it is possible to
	# include a line for only one particular virtual host. For example the
	# following line enables the CGI configuration for this host only
	# after it has been globally disabled with "a2disconf".
	#Include conf-available/serve-cgi-bin.conf
</VirtualHost>

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet
```

```shell
epsi3@ubuntu:~$ systemctl status apache2
● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Fri 2021-04-30 07:42:19 PDT; 7min ago
       Docs: https://httpd.apache.org/docs/2.4/
   Main PID: 7587 (apache2)
      Tasks: 55 (limit: 4618)
     Memory: 6.0M
     CGroup: /system.slice/apache2.service
             ├─7587 /usr/sbin/apache2 -k start
             ├─7588 /usr/sbin/apache2 -k start
             └─7589 /usr/sbin/apache2 -k start
```

## 4.2 Addition du module PHP

```shell
epsi3@ubuntu:~$ sudo apt install libapache2-mod-php
```

```shell
epsi3@ubuntu:~$ sudo -s
root@ubuntu:/home/epsi3# echo "<?php phpinfo() ?>" >  /var/www/html/index.php
root@ubuntu:/home/epsi3# cat /var/www/html/index.php
<?php phpinfo() ?>
```

## 4.3 Addition du module Kerberos

```shell
epsi3@ubuntu:~$ sudo apt install libapache2-mod-auth-kerb
```
![kerberos1](https://i.imgur.com/zvv2VdU.png)

![kerberos2](https://i.imgur.com/mxcvWJq.png)

![kerberos3](https://i.imgur.com/ewJLIDE.png)

# 5 Utilisation de Kerberos avec Apache

```shell

```

## 5.1 Configuration de l’authentification Kerberos

```shell
root@ubuntu:/home/epsi2# kadmin.local -q "addprinc -randkey HTTP/www.epsi.fr"Authenticating as principal root/admin@EPSI.FR with password.
WARNING: no policy specified for HTTP/www.epsi.fr@EPSI.FR; defaulting to no policy
Principal "HTTP/www.epsi.fr@EPSI.FR" created.
root@ubuntu:/home/epsi2# kadmin.local -q "ktadd -k /root/http.keytab HTTP/www.epsi.fr"
Authenticating as principal root/admin@EPSI.FR with password.
Entry for principal HTTP/www.epsi.fr with kvno 2, encryption type aes256-cts-hmac-sha1-96 added to keytab WRFILE:/root/http.keytab.
Entry for principal HTTP/www.epsi.fr with kvno 2, encryption type aes128-cts-hmac-sha1-96 added to keytab WRFILE:/root/http.keytab.
```

```shell
epsi3@ubuntu:~$ sudo cp ~/Downloads/http.keytab /etc/apache2/http.keytab
```

```shell
epsi3@ubuntu:~$ sudo chown www-data /etc/apache2/http.keytab
epsi3@ubuntu:~$ ll /etc/apache2/http.keytab
-rw-r--r-- 1 www-data root 152 avril 30 08:26 /etc/apache2/http.keytab
```

```shell
root@ubuntu:/home/epsi3# apt install krb5-user
```

```shell
root@ubuntu:/home/epsi3# kinit HTTP/www.epsi.fr@EPSI.FR -k -t /etc/apache2/http.keytab
```

![](https://i.imgur.com/QHSpuL6.png)


# Conclusion

On constate qu'avec Kerberos il nous est possible de gérer les utilisateurs de façon centralisée, il nous permet ensuite de generer des tickets pour les utilisateurs, ces tickets sont en quelque sorte des cartes d'identité et possède des propriétés comme un temps d'expiration. Cette mécanique de ticket permet de limiter l'échange d'identifiant tel que le mot de passe.

Néanmoins ces tickets sont conservés côté client, si ces derniers ne sont pas localisés dans un emplacement sécurisé il est possible de les recuperer et d'usurper l'identité des utilisateurs.

De ce que nous avons compris Kerberos est un outil très sécurisé mais il s'appuie sur la sécurité des différentes machines clients et serveurs, si l'une d'entre elle est individuellement piratée il est alors possible de récuperer ces tickets.

Cela n'empeche qu'il limite grandement l'échange d'identifiant il devient donc difficile de pirater le système.