HowTo: Generate Certificate for OpenLDAP and using it for certificate authentication.

LDAPS Server Certificate Requirements

LDAPS requires a properly formatted X.509 certificate. This certificate lets a OpenLDAP service listen for and automatically accept SSL connections. The server certificate is used for authenticating the OpenLDAP server to the client during the LDAPS setup and for enabling the SSL communication tunnel between the client and the server. As an option, we can also use LDAPS for client authentication.

Having spent quite some time to make a TLS work, I thought this may be usefull to some :

Creating Self CA certificate:

1, Create the  ldapclient-key.pem private key :

openssl genrsa -des3 -out ldapclient-key.pem 1024

2, Create the ldapserver-cacerts.pem certificate :

openssl req -new -key ldapclient-key.pem -x509 -days 1095 -out ldapserver-cacerts.pem

Creating a certificate for server:

1, Create the ldapserver-key.pem private key

openssl genrsa -out ldapserver-key.pem

2, Create a server.csr certificate request:

openssl req -new -key ldapserver-key.pem -out server.csr

3, Create the ldapserver-cert.pem certificate signed by your own CA :

openssl x509 -req -days 2000 -in server.csr -CA ldapserver-cacerts.pem -CAkey ldapclient-key.pem -CAcreateserial -out ldapserver-cert.pem

4, Create CA copy for the client:

cp -rpf ldapserver-cacerts.pem   ldapclient-cacerts.pem

Now configure the certificates in slapd.conf, the correct files must be copied on each server:

TLSCACertificateFile /etc/openldap/certs/ldapserver-cacerts.pem
TLSCertificateFile /etc/openldap/certs/ldapserver-cert.pem
TLSCertificateKeyFile /etc/openldap/certs/ldapserver-key.pem
TLSCipherSuite HIGH:MEDIUM:+SSLv2

# personnally, I only check servers from client.
# If you do, add this :
TLSVerifyClient never

Configure certificate for ldap clients

Key : ldapclient-key.pem
Crt : ldapclient-cert.pem