Basics of manual and automatic Certificate Enrollment via Lightweight Directory Access Protocol (LDAP) and Remote Procedure Call / Distributed Common Object Model (RPC/DCOM)

The following describes the process that runs in the background when certificates are requested manually or automatically in order to achieve the highest possible level of automation.

Regardless of whether a manual application is made via the certificate management consoles (certmgr.msc for user and certlm.msc for computer certificates), the process is identical.

Step 1: Query the directory service via LDAP

In the first step, the client establishes an LDAP connection to a domain controller and queries the following information:

• All pKICertificateTemplate Objects (certificate templates) in the Active Directory forest.
• All pKIEnrollmentService objects (enterprise certificate authorities) in the Active Directory forest.
• All msPKI-Enterprise-Oid Objects (Object Identifier) in the Active Directory forest.

This information is all stored in the Configuration partition of the Active Directory forest.

The pKICertificateTemplate and msPKI-Enterprise-OID objects can be used to determine whether the requester is authorized to request ("enroll") and whether an automatic request is to be made ("auto-enroll"). The default settings for making the certificate request are also determined here.

The connection between already existing certificates and the certificate templates is established via the "Certificate Template Information" extension. This contains the object identifier of the certificate template as well as version information. This prevents certificates from being requested twice during autoenrollment, and certificates can be requested again if a serious change has occurred. Replaced certificates can be identified and archived using this information.

For this reason, the "Certificate Template Information" extension must not be used for certificates for which autoenrollment is to be used. be removedotherwise the process will no longer work and the Side effects could occur.

The pKIEnrollmentService objects can be used to determine the certification authorities that offer the certificate templates to be requested, as well as on which computer in the network the certification authority is running. For this purpose the attributes certificateTemplates as well as dNSHostName evaluated.

Step 2: Connection to the target certification authority via RPC/DCOM

In the second step, a key pair and a certificate request are generated based on the requested information and sent to the responsible certification authority. If several certification authorities offer the same certificate template, the decision is made at random unless site awareness has been configured.

The certificate authority can identify the user based on Kerberos authentication and applies the settings specified in the corresponding certificate template with its policy module.

Control of client behavior for autoenrollment

The control of client behavior is controlled by group policy. The group policies exist once for user and for computer settings.

They can be found in our "User" or "Computer Configuration" - "Windows Settings" - "Public Key Policies" - "Certificate Services Client - Autoenrollment".

• The "Configuration Model" causes the autoenrollment process to run at all. If this setting is not configured by a group policy, it is by default on a domain member activates.
• The setting "Renew expired certificates, update pending certificates, and remove revoked certificates" causes expired certificates to be renewed automatically if they were issued by an Active Directory integrated certificate authority. In addition, approved certificate requests are fetched from certification authorities if they are available. Revoked certificates are archived. If this setting is not configured by a group policy, it is by default on a domain member deactivated.
• The "Update certificates that use certificate templates" setting causes certificates to be automatically requested that are enabled for autoenrollment for the requestor. If this setting is not configured by a group policy, it is by default set on a domain member. deactivated.

So, by default, the autoenrollment process automatically replicates all domain members to the Active Directory forest's Public Key Services object when triggered.

Determination of the current configuration

The settings can be checked via the registry on Windows computers. They can be found in the "AEPolicy" value under the following paths:

Path	Description
HKCU\Software\Policies\Microsoft\Cryptography\AutoEnrollment	User settings, configured by group policy
HKCU\Software\Microsoft\Cryptography\AutoEnrollment	User settings, locally configured
HKLM\Software\Policies\Microsoft\Cryptography\AutoEnrollment	Computer settings, configured by group policy
HKLM\Software\Microsoft\Cryptography\AutoEnrollment	Computer settings, locally configured

Settings configured via group policy take precedence over locally configured settings.

A query can be made via the command line.

Example: Settings set by group policy for the currently logged in user account.

reg query ^
HKCU\Software\Policies\Microsoft\Cryptography\AutoEnrollment ^
/v AEPolicy

Example: Computer account settings set by group policy.

reg query ^
HKLM\Software\Policies\Microsoft\Cryptography\AutoEnrollment ^
/v AEPolicy

The values mean in detail:

Value	Description	Result
0x00000000 or not available	AutoEnrollment process is activates „Update certificates that use certificates templates" is deactivated	none automatic request for certificates none Automatic renewal of expired certificates none Automatic collection of approved certificate requests none Automatic archiving of revoked certificates
0x00000001	AutoEnrollment process is activates „Update certificates that use certificates templates" is activates „Renew expired certificates, update pending certificates, and remove revoked certificates" is deactivated	automatic request for certificates none Automatic renewal of expired certificates none Automatic collection of approved certificate requests none Automatic archiving of revoked certificates
0x00000006	AutoEnrollment process is activates „Update certificates that use certificates templates" is deactivated „Renew expired certificates, update pending certificates, and remove revoked certificates" is activates	none automatic request for certificates Automatic renewal of expired certificates Automatic collection of approved certificate requests Automatic archiving of revoked certificates
0x00000007	AutoEnrollment process is activates „Update certificates that use certificates templates" is activates „Renew expired certificates, update pending certificates, and remove revoked certificates" is activates	automatic request for certificates Automatic renewal of expired certificates Automatic collection of approved certificate requests Automatic archiving of revoked certificates
0x00008000	AutoEnrollment is deactivated	none automatic request for certificates none Automatic renewal of expired certificates none Automatic collection of approved certificate requests none Automatic archiving of revoked certificates

Trigger for triggering the autoenrollment process

The triggers for running the autoenrollment process on domain members are:

• When the user logs in (for computers, when the computer account logs in, i.e. at system startup).
• By timer every 8 hours.
• When updating group policies, assuming there has been a change.

These settings can be viewed via the task scheduler under "Microsoft" - "Windows" - "CertificateServicesClient".

Manually running the autoenrollment process

If you do not want to wait for the autoenrollment to be triggered automatically, you can also start it manually. The different ways to run the autoenrollment process are described in the article "Manually running the autoenrollment process" described.

Related links:

• Certificate request basics via Certificate Enrollment Web Services (CEP, CES)

External sources

• Configure certificate auto-enrollment (Microsoft)
• Certificate Enrollment Web Services (Microsoft, archive.org)