Configure Online Responders (OCSP) to use ML-DSA

Applies to: ✅ Windows Server 2025

This article describes how to configure an Online Responder (OCSP) to sign responses by using Module-Lattice-Based Digital Signature Algorithm (ML-DSA) in Active Directory Certificate Services (AD CS). When you configure OCSP with ML-DSA, you enable revocation checking for certificates by using post-quantum signed responses.

Prerequisites

A Subordinate CA configured with ML-DSA and issuing certificates. See Configure a certification authority to use ML-DSA.
A domain-joined member server for the Online Responder, running Windows Server 2025 with the 2026-05 Security update (KB5087539) or later installed. Ensure that the Online Responder role service is installed on this server. The installation steps are the same as for any Online Responder deployment. For detailed guidance, see Implementing an OCSP Responder: Configuring OCSP for use with Enterprise CAs.
An account with permissions to install and configure AD CS role services.
Membership in Domain Admins or equivalent to manage certificate templates.

Create an OCSP Response Signing template with ML-DSA

Before configuring the OCSP responder, create an OCSP Response Signing certificate template that uses ML-DSA.

Open the Certificate Templates console on a machine with AD CS management tools installed.
Right-click the OCSP Response Signing template, and then select Duplicate Template.
On the General tab, enter a Template display name (for example, PQC OCSP Response Signing).
On the Cryptography tab:
- Set Provider Category to Key Storage Provider.
- Set Algorithm name to the desired ML-DSA parameter set (for example, ML-DSA:65).
- The Minimum key size and Request hash fields update automatically.
On the Security tab, grant Enroll and Autoenroll permissions to the computer account of the OCSP responder.
Select OK to save the template.
In the Certification Authority console on the Subordinate CA configured with ML-DSA, right-click Certificate Templates, select New > Certificate Template to Issue, and then select the template you created.

Configure the OCSP revocation provider

The revocation provider configuration is where ML-DSA-specific settings apply. You associate the Online Responder with your ML-DSA Subordinate CA and specify the ML-DSA signing certificate template.

Open the Online Responder Management console (ocsp.msc).
Right-click Revocation Configuration and select Add Revocation Configuration.
On the Name the Revocation Configuration page, enter a name (for example, PQC SubCA OCSP).
On the Select CA Certificate Location page, select Select a certificate for an Existing enterprise CA.
On the Choose CA Certificate page, select Browse CA certificates published in Active Directory, and then select the Subordinate CA configured with ML-DSA.
On the Select Signing Certificate page:
- Select Automatically select a signing certificate.
- Select Auto-Enroll for an OCSP signing certificate.
- Set the Certification authority to the Subordinate CA configured with ML-DSA.
- Set the Certificate Template to the ML-DSA OCSP Response Signing template you created (for example, PQCOCSPResponseSigning).
Select Finish to complete the configuration.
In the Online Responder Management console, under Array Configuration, verify that the Revocation Configuration Status shows:
- Signing Certificate: OK
- Revocation Provider Status: The ML-DSA revocation provider is successfully configured.

Update the AIA extension on the subordinate CA

To direct clients to use the OCSP responder for ML-DSA certificate revocation checking, add the OCSP URL to the Authority Information Access (AIA) extension on the subordinate CA.

On the subordinate CA, open the Certification Authority console (certsrv.msc).
Right-click the CA name and select Properties.
On the Extensions tab, select Authority Information Access (AIA) from the dropdown.
Select Add and enter the OCSP responder URL (for example, http://<ocsp-server-fqdn>/ocsp).
Check Include in the online certificate status protocol (OCSP) extension.
Clear Include in the AIA extension of issued certificates for the OCSP URL entry.
Select OK and restart the CA service when prompted.

Important

The AIA extension change applies only to certificates issued after the change. Previously issued certificates continue to reference the original AIA locations.

Validate ML-DSA OCSP responses

After configuration, verify that the OCSP responder correctly returns ML-DSA signed responses.

Verify by using `certutil`

Enroll for a test certificate from the Subordinate CA by using an ML-DSA template. Export the certificate to a .cer file.
Run the following command to check the revocation status:
```
certutil -verify -urlfetch <certificate-file>.cer
```
In the output, look for the Certificate OCSP section. A valid certificate shows:
```
Verified "OCSP" Time: 0
```
To verify the responder correctly identifies revoked certificates, revoke the certificate on the issuing CA, publish a new certificate revocation list (CRL), and then run the same command. A revoked certificate shows:
```
Revoked "OCSP" Time: 0
```

Verify the ML-DSA signature

To confirm the OCSP response uses an ML-DSA signature, inspect the signing certificate in the Online Responder Management console:

Open ocsp.msc on the OCSP responder server.
Select the revocation configuration, and then select View Signing Certificate.
On the Details tab, confirm the Public key field shows the ML-DSA parameter set and key size.
The Signature algorithm shows the issuing CA's ML-DSA parameter set, confirming the ML-DSA CA issued the signing certificate.

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Last updated on 2026-05-20