Cool Solution - Creation and management of user and Windows certificates

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Produktlogo UCS Version 4.2

Note: Cool Solutions are articles documenting additional functionality based on Univention products. Packages provided by a Cool Solutions Repository are built by Univention, but will not be maintained. Not all of the shown steps in the article are covered by Univention Support. For questions about your support coverage contact your contact person at Univention before you want to implement one of the shown steps.

Also regard the legal notes at Terms of Service.

Users and Windows computers within the UCS domain can be supplied with a custom certificate using the UMC. The private and public part of the certificate will be stored in the filesystem of the Domaincontroller Master, while the public part will be also imported into the LDAP. The certificates can then be used for e.g. authentication, signing e-mails, or securing connections to the Windows computer.

This documentation guide you through the installation of the user and windows certificate extension on your system and creating individual certificates. Certificates are created as DER and PEM files.

Installation

The software is designed to operate on the UCS DC Master. To install the packages you need to enable the Cool Solution repository at first.

There has been a change in the certification mechanism introduced with Errata 213 for UCS 4.1. Please ensure that you are at least on this Errata level before following the next steps.

Next, you must install the package univention-ldap-usercert on the DC Master server and should install the package on every additional DC Backup servers. This can be achieved by using either the UMC module Package management or invoke the following command:

univention-install univention-ldap-usercert

Additionally you must install the packages univention-usercert on the DC Master. Optionally, you can also install univention-windowscert for the creation of certificates for windows clients. Again you can either use the UMC module Package management or the command line:

univention-install univention-usercert univention-windowscert

During the installation, new UCR variables will be created (see below) and the Univention directory listener daemon will be restarted.

If not run automatically, check if joinscripts must be executed.

univention-run-join-scripts

Managing user certificates

To create a user certificate, open the [Options] tab in the user's LDAP object and select "Public key infrastructure account".

Enable "Public key infrastructure account"

Now save and reopen the user object and switch to the User Certificate tab and select "Create/Revoke User Certificate".

Create the user certificate

When saving, the certificate is created and saved in the directory provided in ssl/usercert/certpath in a subdirectory with the user's UID. By default, only the user itself and the group entered in ssl/usercert/admingroup have read permission on the files. It is recommended to create a file share of the folder containing the certificates, so users can access them remotely.

Note: Optionally, the standard valid time of the certificate can be overwritten here. If the field is left blank, the standard valid time from the UCR variable ssl/usercert/days will be used.

When a certificate is to be revoked, it is sufficient to untick "Create/Revoke User Certificate". The certificate files are removed from the LDAP, but not deleted from the filesystem. If the UCS root CA was used to sign the user's certificate, an entry is made into the Certificate Revocation List specified by /etc/univention/ssl/ucsCA/crl/.

When a certificate needs to be renewed, it is sufficient to tick "Renew User Certificate" and save the changes made. The old certificate will then be revoked and a new one will be created with the settings from the former certificate.

Managing windows computer certificates

To create a computer certificate, open the Certificate tab on the computer's LDAP option and select "Create/Revoke Certificate".

Create the computer certificate

When a certificate is to be revoked, it is sufficient to untick "Create/Revoke Certificate". The certificate files are removed from the LDAP, but not deleted from the filesystem. If the UCS root CA was used to sign the computer's certificate, an entry is made into the Certificate Revocation List specified by /etc/univention/ssl/ucsCA/crl/.

When a certificate needs to be renewed, it is sufficient to tick "Renew Certificate" and save the changes made. The old certificate will then be revoked and a new one will be created with the settings from the former certificate.

Convert certificates

It is also possible to upload certificates for users and windows computers in the UMC. In this case, the certificates have to be DER encoded before the upload. If you have a PEM encoded certificate, you can convert your certificate to DER with openssl on the commadline:

openssl x509 -in /path/to/certificate.PEM -out /path/to/certificate.DER -outform DER

UCR variables and their functionality

During the installation, several new UCR variables will be created. They are as follows:

UCR variable Default value Description
User certificate
ssl/usercert/UID/extensionsfile <empty> Apply the custom settings only to users named here.
ssl/usercert/admingroup DC Backup Hosts Besides the owner of the certificate, this group has read permissions on the certificate files.
ssl/usercert/ca ucsCA Folder where the Root CA files are stored (located in ssl/usercert/sslbase).
ssl/usercert/certldapmapping/cn uid Maps, which identifier from the user's CN is mapped with the user certificate.
ssl/usercert/certldapmapping/email mailPrimaryAddress Maps, which e-mail address is mapped with the user certificate.
ssl/usercert/certldapmapping/locality l Maps, which location is mapped with the user certificate.
ssl/usercert/certldapmapping/organization o Maps, which organization is mapped with the user certificate.
ssl/usercert/certldapmapping/organizationalunit <empty> Maps, which business unit is mapped with the user certificate.
ssl/usercert/certldapmapping/state <empty> Maps, which state is mapped with the user certificate.
ssl/usercert/certpath /etc/univention/ssl/user Default path where the user certificates are saved in a UID labeled subdirectory.
ssl/usercert/days 1825 Default time that a certificate is valid. Can be overwritten in the user's UMC object.
ssl/usercert/default/country Defaults to Root CA's country By default, no LDAP mapping exists for this variable, the value from ssl/country will be used.
ssl/usercert/default/email Defaults to Root CA's e-mail By default, no LDAP mapping exists for this variable, the value from ssl/email will be used.
ssl/usercert/default/locality Defaults to Root CA's location By default, no LDAP mapping exists for this variable, the value from ssl/locality will be used.
ssl/usercert/default/organization Defaults to Root CA's organization By default, no LDAP mapping exists for this variable, the value from ssl/organization will be used.
ssl/usercert/default/organizationalunit Defaults to Root CA's business unit By default, no LDAP mapping exists for this variable, the value from ssl/organizationalunit will be used.
ssl/usercert/default/state Defaults to Root CA's state By default, no LDAP mapping exists for this variable, the value from ssl/state will be used.
ssl/usercert/extensionsfile <empty> Overwrite the default openSSL settings with custom settings.
ssl/usercert/ldapimport yes If set to yes/true, the public certificate is imported into the LDAP.
ssl/usercert/passwordchars <empty> Any number can be entered here to specify the password length.
ssl/usercert/pkcs12/chain yes Whether the PKCS12 chain is saved in the certificate.
ssl/usercert/sslbase /etc/univention/ssl/ SSL root directory.
Windows certificate
ssl/windowscert/UID/extensionsfile <empty> Apply the custom settings only to computers named here.
ssl/windowscert/admingroup DC Backup Hosts Besides the owner of the certificate, this group has read permissions on the certificate files.
ssl/windowscert/ca ucsCA Certificate to sign the computer certificate with.
ssl/windowscert/certldapmapping/cn cn Maps, which identifier from the computer's CN is mapped with the computer certificate.
ssl/windowscert/certldapmapping/email <empty> Maps, which e-mail address is mapped with the computer certificate.
ssl/windowscert/certldapmapping/locality <empty> Maps, which location is mapped with the user certificate.
ssl/windowscert/certldapmapping/organization <empty> Maps, which organization is mapped with the user certificate.
ssl/windowscert/certldapmapping/organizationalunit <empty> Maps, which business unit is mapped with the user certificate.
ssl/windowscert/certldapmapping/state <empty> Maps, which state is mapped with the user certificate.
ssl/windowscert/certpath /etc/univention/ssl/windows-hosts Path where the certificates are saved. Only the computer account and the group in ssl/windowscert/admingroup can access this directory.
ssl/windowscert/days 1825 Default time that a certificate is valid. Can be overwritten in the computers's UMC object.
ssl/windowscert/extensionsfile <empty> Overwrite the default openSSL settings with custom settings.
ssl/windowscert/ldapimport yes Whether the public certificate should be imported automatically.
ssl/windowscert/passwordchars <empty> Any number can be entered here to specify the password length.
ssl/windowscert/pkcs12/chain yes Whether the PKCS12 chain is saved in the certificate.
ssl/windowscert/sslbase /etc/univention/ssl/ Base directory where all SSL certificates are saved.

Apache and SSL certificates

It is possible to configure the Apache webserver so that only users with a valid certificate, imported in the user web browser, can access a webpage or directory using HTTPS.

To configure this, either expand an existing site or create a new one in /etc/apache2/sites-available.

Attention: When expanding an existing site, please make sure that the file is not managed by a UCR template, as it may be overwritten when corresponding UCR variables are changed! Either expand the template file (handle with care!) or create a new site!

Put the following code into the site file:

# CA Certificates for Client Auth
SSLCACertificateFile /etc/univention/ssl/ucsCA/CAcert.pem
SSLCACertificatePath /etc/univention/ssl/ucsCA/

# Revocation list
SSLCARevocationFile  /etc/univention/ssl/ucsCA/crl/crl.pem

# Protected directory
<Directory /var/www/statistik>
        Options Indexes FollowSymLinks MultiViews
        Require all granted
        SSLVerifyClient require
  SSLVerifyDepth       5
  SSLOptions           +FakeBasicAuth
  SSLRequireSSL
</Directory>

If a new site is created, the site must be enabled with

a2ensite NEW_SITE_NAME

After activating a new site, or expanding an existing one, the Apache webserver must be reloaded:

invoke-rc.d apache2 reload

Handling of revoked certificates

Apache only checks the certificate revocation list when the service is reloaded. It is adviced to create a cronjob using UCR that reloads the service on a daily basis:

ucr set \
cron/reload-apache2/command="invoke-rc.d apache2 reload" \
cron/reload-apache2/time="0 0 * * *"

The above cronjob reloads Apache once a day at midnight.

Archive

  • There is a version of this article for UCS 4.1.
  • There is a version of this article for UCS 4.0
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