All posts in category Encryption

Microsoft AD CS Adds Post-Quantum Cryptography Support with ML-DSA

Despite predictions of its decline, Microsoft Active Directory Certificate Services (AD CS) continues to evolve. Following significant enhancements introduced in late 2025, including CRL partitioning and support for 16K database pages, the May 2026 update adds another important capability: support for Post-Quantum Cryptography (PQC).

ML-DSA

Specifically, the May 2026 update adds support for ML-DSA-44, ML-DSA-65, and ML-DSA-87 in Windows Server 2025 for AD CS. This enables administrators to begin evaluating post-quantum cryptographic algorithms and assessing PQC readiness in enterprise PKI environments

Configuration

After applying the May 2026 update to an issuing Certification Authority (CA), administrators will find new PQC algorithms under the Algorithm name drop-down list, as shown here.

Note: If you don’t see these new algorithms, ensure you have selected Key Storage Provider from the Provider Category drop-down list. In addition, ensure that you select Signature on the Request Handling tab.

Test Results

Initial testing across common enterprise certificate scenarios produced mixed results. While PQC works well in some scenarios, other workloads still show limitations.

Code Signing

Code signing with an ML-DSA-44 certificate issued by AD CS works perfectly. For example, I can use Set-AuthenticodeSignature to sign a PowerShell script, as shown here.

Viewing the file’s properties shows that the encryption algorithm used to sign the file was ML-DSA-44, as expected.

IIS

TLS-based workloads proved more challenging. Attempts to configure an HTTPS binding in IIS failed with the following error message.

There was an error while performing this operation. A specified logon session does not exist. It may already have been terminated. (Exception from HRESULT: 0x80070520).

RRAS and SSTP

Similar limitations occurred when testing remote-access VPN scenarios using RRAS and SSTP. Specifically, configuring a PQC TLS certificate for SSTP in RRAS failed. Although I was able to assign the certificate using Set-RemoteAccess, the RemoteAccess service failed to start.

Remote Desktop

Unfortunately, using PQC certificates for RDP also fails. Although I could assign the PQC certificate to the RDP listener, clients fail to connect using RDP and return the following error message.

This computer can’t connect to the remote computer. Try connecting again. If the problem continues, contact the owner of the remote computer or your network administrator.

Error code: 0x904
Extended error code: 0x7

Summary

The May 2026 update marks an important milestone for AD CS by introducing initial support for PQC algorithms, allowing organizations to begin evaluating ML-DSA certificates in enterprise environments. Early testing shows promising results for signing scenarios such as code signing; however, broader infrastructure workloads, including TLS, VPN, and Remote Desktop, remain limited today. Although PQC support is still in its early stages, these updates demonstrate Microsoft’s ongoing investment in AD CS and provide administrators with an opportunity to begin preparing their PKI environments for the post-quantum future. Additional PQC enhancements, including ML-KEM support and broader ecosystem integration, are anticipated in future Windows updates.

Additional Information

Microsoft May 2026 Security Updates (KB5087539)

Post Quantum Cryptography in the Enterprise

The Case for 6-Day Public TLS Certificates

In February 2025, Let’s Encrypt introduced the option to enroll for public TLS certificates with a 6-day validity period. This represents a significant shift toward short-lived certificates and aligns with the broader industry trend of reducing certificate lifetimes to improve security. While this may seem aggressive at first glance, organizations that have embraced automation will find that extremely short-lived certificates offer compelling security and operational advantages in some scenarios.

Benefits

Extremely short-lived TLS certificates offer several important security and operational benefits, particularly for organizations that have already embraced automation for certificate lifecycle management. Key advantages include:

Minimized Risk of Key Compromise – 6-day certificates dramatically reduce the exposure window of private key compromise events, giving attackers a limited window of opportunity to exploit key access.
Automation Validation – Short-lived certificates force organizations to adopt and validate automated enrollment and renewal processes, ensuring that certificate lifecycle management is reliable and resilient.
IP Address Support – 6-day TLS certificates from Let’s Encrypt support IP addresses, allowing administrators to secure workloads that do not have entries in DNS.

Use Cases

6-day TLS certificates are well-suited for a range of modern workloads, especially those that benefit from frequent key rotation, automation, and dynamic provisioning. 6-Day TLS certificates are well-suited for the following workloads:

High Value Resources – Using 6-day TLS certificates is beneficial for high-security or sensitive workloads where frequent key rotation is desired.
Test Labs – High-frequency certificate rotation allows for thorough testing of automation processes to ensure operational reliability of production deployments. Rapid iteration of 6-day TLS certificates allows administrators to identify potential issues and implement changes before long-term certificates expire.
Ephemeral Infrastructure – 6-day TLS certificates work well with dynamic workloads such as containers, where environments are rapidly provisioned and destroyed. These hosts might only live for a few hours or days, making short-lived certificates an ideal choice in this scenario.
Workload Bootstrapping – 6-day TLS certificates can be used where a certificate is required only to perform initial configuration. For example, an IP-based TLS certificate can be used to configure TLS services, then later migrated to a long-term certificate when DNS is configured and the service is placed into production.

Enterprise Usage

Administrators will find that 6-day public TLS certificates work well with many popular Windows Server workloads. Here are a few examples.

Always On VPN – Enterprise secure remote access is a popular target for attackers because the service is exposed to the Internet. Using 6-day TLS certificates ensures frequent key rotation, reducing exposure to key compromise.
Remote Desktop Services – Many organizations continue to use Remote Desktop Gateway to provide access to on-premises applications, another workload that is exposed to the Internet. Using 6-day TLS certificates is equally effective in this scenario.

What About DirectAccess?

Although DirectAccess would be another ideal Windows Server workload for 6-day TLS certificates, my testing shows that it does not work. The root cause is that 6-day TLS certificates from Let’s Encrypt do NOT include subject information (the field is blank). Unfortunately, because of the way in which DirectAccess validates this certificate, it requires information in this field. More details can be found here.

https://directaccess.richardhicks.com/2026/03/16/directaccess-iphttps-and-lets-encrypt-6-day-certificates/

Summary

If you are automating certificate enrollment and renewal, it shouldn’t matter if the certificate is valid for 6 days or 60 days. In fact, shorter lifetimes can significantly improve your security posture by minimizing risk and enforcing operational discipline around certificate management. Organizations that invest in automation today will be well-positioned to adopt even shorter certificate lifetimes in the future, while those relying on manual processes will find it increasingly difficult to keep up.

Questions?

Do you have questions about certificate lifecycle automation in your environment? I’m happy to help you validate your approach and address any challenges you’re encountering. Fill out the form below, and I’ll provide you with more information.

Additional Information

Let’s Encrypt Issues First Six-Day Certificate

DirectAccess IP-HTTPS and Let’s Encrypt 6-Day TLS Certificates

The Case for Short-Lived Certificates in the Enterprise

2 Comments

by Richard M. Hicks on May 4, 2026 • Permalink

Posted by Richard M. Hicks on May 4, 2026

https://directaccess.richardhicks.com/2026/05/04/the-case-for-6-day-public-tls-certificates/

DirectAccess IPHTTPS and Let’s Encrypt 6-Day Certificates

I’ve written extensively about how public TLS certificate lifetimes will drop to just 47 days by March 2029. Before then, we’ll see certificate lifetimes gradually drop from the current 398 days to 200 days on March 15, 2026, and then to 100 days on March 15, 2027. In preparation for this, I’ve been working with many customers to deploy automated certificate enrollment and renewal solutions to eliminate the need for manual intervention. Interestingly, Let’s Encrypt now offers extremely short-lived certificates that are good for just 6 days! While they work just fine for Always On VPN, I discovered they will not work for DirectAccess.

6-Day Certificate

After successfully enrolling for a 6-day TLS certificate from Let’s Encrypt (I used CertKit, BTW!), I encountered an error when trying to assign the short-lived certificate to the IP-HTTPS listener in the DirectAccess configuration. Specifically, when running the Set-RemoteAccess PowerShell command, I received the following error.

Set-RemoteAccess: The parameter is incorrect.

Further investigation showed that I could install other public TLS certificates just fine. For some reason, though, DirectAccess did not like this new 6-day certificate.

Missing Subject Name

After digging a bit deeper, I realized the Subject field of the new 6-day Let’s Encrypt certificate was empty.

Subject vs. SAN in Modern TLS

Modern TLS clients rely entirely on the Subject Alternative Name (SAN) field for identity validation, and the older practice of matching against the certificate’s Subject field has been phased out for many years. Many certificate authorities, including Let’s Encrypt, now leave the Subject field empty because it no longer serves a functional purpose in current TLS implementations. DirectAccess still expects this field to contain data and does not properly fall back to SAN‑only validation. As a result, any certificate with an empty Subject field, such as the new 6‑day certificates from Let’s Encrypt, will fail when applied to the DirectAccess IP‑HTTPS listener.

Workaround

Admittedly, using 6-Day public TLS certificates for DirectAccess is extreme and likely overkill for this workload. The good news is that DirectAccess still works perfectly with 90-day Let’s Encrypt certificates, so the lack of 6-day certificate support should not be impactful.

CertKit

Have you heard about CertKit? CertKit, an online service for automating Let’s Encrypt certificate enrollment and renewal, has added support for Always On VPN and DirectAccess. Find details on leveraging it for public TLS certificates for these solutions here.

Additional Information

Always On VPN SSTP with Let’s Encrypt Certificates

Always On VPN and 47-Day Public TLS Certificates

The Case for Short-Lived Certificates in Enterprise Environments

CertKit Agent Support for Always On VPN SSTP and DirectAccess IP-HTTPS TLS Certificates

Richard M. Hicks Consulting, Inc.

Microsoft MVP

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All posts in category Encryption

Microsoft AD CS Adds Post-Quantum Cryptography Support with ML-DSA

ML-DSA

Configuration