Tuesday, 7 March 2017

Let's Encrypt SSL Recipes -- 389 Directory Server with LDAPS


These instructions are aimed at installing 389 Directory Server with the latest release of Red Hat Enterprise Linux or CentOS (currently release 7).
I assume that you have already created SSL certificates using Let's Encrypt as per the first part of this series.

389 Directory Server Installation

To install the directory server:

yum -y install 389-ds-base 389-admin 389-admin-console 389-console 389-ds-console xauth

The 389 directory server home page is here: http://directory.fedoraproject.org/ and the installation guide is here: https://access.redhat.com/documentation/en-US/Red_Hat_Directory_Server/9.0/html/Installation_Guide/index.html

Directory Server Setup

To set up the 389 directory server, a script is provided:


Run this script once and only once! It will ask you for some port numbers and a directory manager password. If you forget these then the only option is to rebuild the directory server.

Note that administering the 389 directory server is done using the administration console. To run this remotely requires an authenticated remote X11 session, hence the installation of "xauth". The 389 administration console is a Java program so you can install it on any desktop PC and do the administration remotely if you don't have a local X11 server.

During the setup process you will be asked some questions. The defaults should mostly be sufficient. Some questions you need to pay attention to are as follows:
Please enter the administrator ID for the configuration directory
server.  This is the ID typically used to log in to the console.  You
will also be prompted for the password.

Configuration directory server
administrator ID [admin]: 
Password (confirm):

You should choose the default administrator ID here admin and also make sure that you remember this password, it will be important later.
Each instance of a directory server requires a unique identifier.
This identifier is used to name the various
instance specific files and directories in the file system,
as well as for other uses as a server instance identifier.

Directory server identifier [ldap]:

This instance name is important -- we will need it later. For the time being we will put that instance name into a shell variable. I stay with the default instance name ldap because that seems to be a pretty obvious choice:
The suffix is the root of your directory tree.  The suffix must be a valid DN.
It is recommended that you use the dc=domaincomponent suffix convention.
For example, if your domain is example.com,
you should use dc=example,dc=com for your suffix.
Setup will create this initial suffix for you,
but you may have more than one suffix.
Use the directory server utilities to create additional suffixes.

Suffix [dc=mysite,dc=com]:

This suffix becomes the Base DN of your directory. You should use the format above -- e.g. mysite.com becomes dc=mysite,dc=com. Of course substitute your own domain name in there for mysite.com.
Certain directory server operations require an administrative user.
This user is referred to as the Directory Manager and typically has a
bind Distinguished Name (DN) of cn=Directory Manager.
You will also be prompted for the password for this user.  The password must
be at least 8 characters long, and contain no spaces.
Press Control-B or type the word "back", then Enter to back up and start over.

Directory Manager DN [cn=Directory Manager]: 
Password (confirm):

This password is very important because it's the one that you will use to create directory entries, later.
The Administration Server is separate from any of your web or application
servers since it listens to a different port and access to it is

Pick a port number between 1024 and 65535 to run your Administration
Server on. You should NOT use a port number which you plan to
run a web or application server on, rather, select a number which you
will remember and which will not be used for anything else.

Administration port [9830]:

Again this port number is important. Picking the default of 9830 seems to be a good choice.

Firewall Rules

One thing that I always forget on a RHEL or CentOS server is to set the correct firewall rules. This recipe allows access to the firewall on the LDAP and LDAPS ports (we may disable LDAP later):

# Add rules to the public zone to allow LDAP and LDAPS
firewall-cmd --permanent --zone=public --add-service=ldap
firewall-cmd --permanent --zone=public --add-service=ldaps
firewall-cmd --permanent --zone=public --add-port=9830/tcp
firewall-cmd --reload

# Check the firewall rules created by firewalld
iptables -L -n

# Check the rules loaded into firewalld
firewall-cmd --state
firewall-cmd --zone=public --list-all

Note that the port for LDAP is 389 and the port for LDAPS is 636 so you should check that these are both enabled in your firewall rule set.

Certificate Installation

Firstly, here are some references that I read in order to create these recipes. You may also find them helpful:

PKCS12 file

There are many different certificate file formats. Let's Encrypt provides certificates in PEM format, while 389 Directory Server requires them in PKCS12 format. We can use OpenSSL to convert between the two. We will put the converted certificate into a temporary directory while we are working on it:

# Make the temporary directory to store the PKCS12 file
mkdir -p $TMPDIR
chmod 700 $TMPDIR

# Make the PKCS12 file from the letsencrypt PEM files
rm -f $TMPDIR/$SITE.p12
openssl pkcs12 -export -in /etc/letsencrypt/live/$SITE/cert.pem \
    -inkey /etc/letsencrypt/live/$SITE/privkey.pem \
    -nodes -passout pass: -name $SITE -out $TMPDIR/$SITE.p12

As in all of these recipes, replace mysite.com with your actual server name, the name that you obtained the certificate for. This should be exactly the same hostname that you ask your LDAP clients to connect to the server with, otherwise certificate verification will fail.

Import the PKCS12 file into 389 Directory Server

Importing the PKCS12 file into 389 Directory Server is done using the pk12util command line utility program provided with the nss-tools package -- this should already have been installed as part of the 389 Directory Server installation. The first time you do this it will ask you for a password which will become the password for the NSS key store. You will need to remember this password (along with the admin and cn=Directory Manager passwords that you created when you set up the directory). A password manager program such as keepass may be useful at this point.
# Import the PKCS12 file into 389DS
# This will require the Password for the 389DS NSS Certificate DB
pk12util -d /etc/dirsrv/slapd-$LDAPINSTANCE -i $TMPDIR/$SITE.p12

Import the Certificates into 389 Directory Server

We can now separately import the certificates into 389 Directory Server. When we do this, we give the certificates some specific nicknames:
# Import the certs separately with standard certificate nicknames
certutil -A -d /etc/dirsrv/slapd-$LDAPINSTANCE/ -n "ca_cert" -t "C,," -i /etc/letsencrypt/live/$SITE/chain.pem
certutil -A -d /etc/dirsrv/slapd-$LDAPINSTANCE/ -n "Server-Cert" -t ",," -i /etc/letsencrypt/live/$SITE/cert.pem

Check the Keys and Certificates

To check that the keys and certificates have been imported correctly, you can list the contents of the key store and the certificate store using these commands. Note that to list the contents of the key store you will need to provide the key store password:

# Check on keys and certs imported into 389DS
# This will require the Password for the 389DS NSS Certificate DB
certutil -K -d /etc/dirsrv/slapd-$LDAPINSTANCE
certutil -L -d /etc/dirsrv/slapd-$LDAPINSTANCE
In case you ever need to delete keys or certificates from the site, you can use these commands:

# In case you need to delete keys or certificates, do this
certutil -d /etc/dirsrv/slapd-$LDAPINSTANCE -F -n 'key_nickname'
certutil -d /etc/dirsrv/slapd-$LDAPINSTANCE -D -n 'certificate_nickname'

Enable LDAP Security

Most of these recipes follow the guide here: http://directory.fedoraproject.org/docs/389ds/howto/howto-ssl.html

Before you start, shut down the directory server as follows:
systemctl stop dirsrv@ldap

You now need to edit the file /etc/dirsrv/slapd-ldap/dse.ldif. This is the raw configuration data that is loaded into your directory server when it boots.
The format of this file is:
dn: (some dn)
attribute1: value1
attribute2: value2
... etc
(blank line before the next dn)

So when you're editing this file, maintain the correct format. You can insert and remove lines but leave the blank lines in place, and don't add any extra blank lines. To turn on and enable LDAP security, you need to edit this file, and change some entries by adding or removing attributes.


Add this attribute:
nsslapd-security: on


Set all of these attributes:

nsSSLSessionTimeout: 0
nsSSLClientAuth: off
nsSSL3: off
nsSSL2: off
Remove the sslVersionMin, sslVersionMax and nsSSL3Ciphers attributes if they are present.


You will need to add this as a new entry. It should look like this:

dn: cn=RSA,cn=encryption,cn=config
objectClass: top
objectClass: nsEncryptionModule
nsSSLPersonalitySSL: Server-Cert
nsSSLActivation: on
nsSSLToken: internal (software)
cn: RSA
Note that Server-Cert matches the nickname of the certificate that you imported using certutil above (after the -n parameter). You don't need to specify the nickname of the CA signing certificate, Directory Server and NSS will work out this chain correctly provided all CA and chain elements are in the certificate database.

Specify the NSS Key Store Password

You need to put the password for the NSS key store into a file so that the server can read it when it boots.

The file name is /etc/dirsrv/slapd-ldap/pin.txt (in the same directory as dse.ldif) and it contains the password in this format:

Internal (Software) Token:MySecretPassword
This password is the same one as the password that you gave when you first imported the key into the key store using pk12util.

Restart the Directory Server

systemctl restart dirsrv@ldap

Check That Security Is Turned On

To check that security is turned on you can try these commands:

Search for the nssldap-security entry

ldapsearch -x -W -D 'cn=Directory Manager' -H ldap://localhost/ -b 'cn=config' -s base nsslapd-security

This should report:
nsslapd-security: on

Search for the Encryption Config

ldapsearch -x -W -D 'cn=Directory Manager' -H ldap://localhost/ -b 'cn=encryption,cn=config' -s base

This should report a large entry with lots of nssslenabledciphers attributes, and also the following:
nsSSL2: off
nsSSL3: off
nsTLS1: on
sslVersionMin: TLS1.0
sslVersionMax: TLS1.2

Search for the RSA config

ldapsearch -x -W -D 'cn=Directory Manager' -H ldap://localhost/ -b 'cn=RSA,cn=encryption,cn=config' -s base

This should report something like the following:
dn: cn=RSA,cn=encryption,cn=config
objectClass: top
objectClass: nsEncryptionModule
nsSSLPersonalitySSL: Server-Cert
nsSSLActivation: on
nsSSLToken: internal (software)
cn: RSA

Do an LDAPS search

Now that you have SSL/TLS configured on your LDAP server you should be able to do searches like this:

ldapsearch -x -H ldaps://localhost/ -s base -b '' namingContexts
Note the ldaps part of the URL (-H parameter) which specifies to connect on port 636 and set up an encrypted SSL session with the LDAP server.

Do the same search with the ldaps:// URL and then gain with the ldap:// URL (non-SSL mode) to check that you get the same results.


If you want to restrict your directory server to doing SSL sessions only, you could remove the open port 389 from the firewall configuration and leave only port 636 open.

firewall-cmd --permanent --zone=public --remove-service=ldap
firewall-cmd --reload
firewall-cmd --zone=public --list-all

Test the Certificate Using OpenSSL

OpenSSL has a useful tool for probing SSL enabled sites and checking their certificates. You should do this from outside of your new LDAP machine:

openssl s_client -connect mysite.com:636 -showcerts </dev/null
This command will establish a connection to your LDAP server on the LDAPS port (636) and print out the certificates. Because it reads input from /dev/null it will finish once the connection is established.

You should get 2 certificates printed out. One will be your server certificate and will begin like this:

 0 s:/CN=mysite.com
   i:/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
... the other will be the Let's Encrypt authority certificate and will begin like this:

 1 s:/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
   i:/O=Digital Signature Trust Co./CN=DST Root CA X3
As long as you see both of those certificates you should be OK. Towards the end of the output there will be a block like this:

New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-GCM-SHA384
This is telling you about the encryption negotiated between s_client and your LDAP server. In this case it's showing a good level of security with TLS v1.2 being enabled as well as a cipher from the AES-256 cipher suite being negotiated with SHA384 as the signing hash algorithm -- all current industry standard security.

Using 389 Directory Server

There are plenty of articles about how to use the Directory Server console so I won't go into details here. This is a tool that you can use to manage the directory server.

The directory server can be used as an authentication method for many applications, including:
  • redmine and JIRA
  • gitlab
  • Many CRM systems
... etc. The usual information that you will need to provide for these programs when you are setting them up for LDAP access to your new directory server are:
  • Hostname -- mysite.com or whatever your directory server host name is.
  • Port -- 636 and you will need to check the "SSL" or "LDAPS" options.
  • Base DN -- this was set by you when you ran the configuration script.
  • Search DN -- leave this empty.
  • Search Password -- leave this empty.
  • LDAP Filter -- you probably want to use something like objectClass=inetOrgPerson
  • Mapping attributes. You may or may not need to do this but some attributes that you may need to provide are:
    • Login Attribute: uid
    • First Name Attribute: givenName
    • Surname Attribute: sn
    • Email Attribute: mail
  • Active Directory Mode -- what this means may depend on your application but some applications use this to turn on a whole bunch of options. You should turn this off.

Extra Software

There are some extra applications that I find useful to install on a Directory Server. These are:
  • Self Service Password -- this application allows a simple interface for users to change their password.
  • phpLDAPAdmin -- a web application to add/update/remove directory entries, gives you full management over your directory server without having to use the directory server console. You can install this directly from the EPEL repository like this:
yum -y install phpldapadmin
After installing you may want to trim down the templates that are in /usr/share/phpldapadmin/templates/creation/ I generally remove all of them except the following:
  • alias.xml
  • inetOrgPerson.xml
  • organizationalRole.xml
  • ou.xml
  • posixAccount.xml
  • posixGroup.xml
  • simpleSecurityObject.xml

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