Wednesday, May 24, 2023

Adding SSL/TLS certificates to Openldap on localhost using Ubuntu Linux 22.04.2

I wanted to install ssl/tls certificates on my openldap installation that I had running on localhost as a demo, but the information I found on the Web was mostly out of date. Another approach is to use letsencrypt, but that is for registered domain names and won't work with localhost, so I will be using self-signed certificates in this post.


You will need to have installed openldap and openssl. If you haven't then do so now:

sudo apt install openssl slapd

Create a certificate authority (CA) to sign your certificates

There is a script in openssl for doing this. Nowadays it is called I found it in /usr/lib/ssl/misc/, but it might be somewhere else on your machine. You can find it with:

sudo find / -name

Once you have the path to it, create a directory to hold the CA. I created one in /var/myca:

sudo mkdir -p /var/myca
cd /var/myca
Now invoke the script:

sudo /usr/lib/ssl/misc/ -newca

When it prompts for a certifcate filename just hit return. It will ask you some certificate type questions, including a passphrase. Give it something simple so you can remember it. (Remember this is just for testing. On production you'll need a secure passphrase.) It will create a directory called demoCA inside /var/myca.

Create a certificate for openldap using the CA

sudo   openssl req -new -nodes -keyout newreq.pem -out newreq.pem

Again, you have to answer all the tedious certificate questions. When it has finished you should have newreq.pem in the /var/myca directory. Now sign the request:

sudo /usr/lib/ssl/misc/ -sign

This creates newcert.pem

Copy the certificates and key to where openldap can find them

Create a directory to hold them for openldap. I chose /etc/openldap/certs. Create it if it is not there:

sudo mkdir -p /etc/openldap/certs

Now copy the certificates over:

cd /etc/openldap/certs
sudo cp /var/myca/demoCA/cacert.pem .
sudo mv /var/myca/newcert.pem servercrt.pem
sudo mv /var/myca/newreq.pem serverkey.pem
sudo chmod 600 serverkey.pem 
sudo chown openldap:openldap *
ls -l

This produces:

-rw-r--r-- 1 openldap openldap 4730 May 25 11:49 cacert.pem
-rw-r--r-- 1 openldap openldap 4751 May 25 11:50 servercrt.pem
-rw------- 1 openldap openldap 2843 May 25 10:22 serverkey.pem

Allow Openldap to read this directory

Nowadays Openldap is controlled by apparmor, which restricts which directories openldap, aka slapd, can access. So we have to tell it about this new directory of certificates we just created. In /etc/apparmor.d you should find a file called usr.sbin.slapd, which is divided into sections, one of which is called "# ldap files". After that are a couple of lines. Add this line in bold using your favourite editor to tell it about all the files in /etc/openldap/certs:

  # ldap files
  /etc/ldap/** kr,
  /etc/ldap/slapd.d/** rw,
  /etc/openldap/certs/* r,

Now restart slapd to get it to see the directory:

sudo systemctl restart slapd

Update the openldap config to point to the certificates and key

Create a file add_ssl.ldif using nano or vi, with this content:

dn: cn=config
changetype: modify
replace: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/openldap/certs/cacert.pem
replace: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/openldap/certs/serverkey.pem
replace: olcTLSCertificateFile
olcTLSCertificateFile: /etc/openldap/certs/servercrt.pem

Now load it:

sudo ldapmodify -Q -Y EXTERNAL -H ldapi:/// -f add_ssl.ldif -W

It will respond with:

[sudo] password for username: 
Enter LDAP Password: 
modifying entry "cn=config"

If it says:

ldap_modify: Other (e.g., implementation specific) error (80)

check in the last lines of syslog (tail /var/log/syslog) to see if apparmor is denying access. If so, check your steps in "Allow Openldap to read this directory" above.

Tell Openldap where the CA certificate is

Edit /etc/ldap/ldap.conf and set the variable TLS_CACERT to /etc/openldap/certs/cacert.pem, then restart slapd:

sudo systemctl restart slapd

Your Openldap installation should now be ready to use SSL!

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