Post-quantum: Microsoft urges testing certificates and PKI now

Microsoft published a call on October 8, on its security blog, to start testing certificate infrastructure against post-quantum cryptography now. The company notes that preparation focuses mostly on encryption, while authentication will also have to switch algorithms: certificates, certificate authorities, public key infrastructures (PKI) and hardware security modules (HSMs). The text offers recommendations, with no deadline or obligation. It presents this preparation as a multi-year planning effort.

What could go wrong

Post-quantum certificates and their chains are larger, Microsoft points out. The company lists the questions that testing should answer. Can applications read and validate these certificates? What effect will heavier chains have on the size of TLS exchanges, performance, storage and traffic inspection tools? Will internal PKI procedures, certificate management tools and HSMs keep up? Microsoft above all warns about hidden dependencies: embedded devices, industrial IT (OT), in-house applications, third-party services and security appliances. Some may have long life cycles or rely on hard-coded cryptographic choices.

A pilot program and first Windows tools

Since August 27, a pilot program has allowed approved certificate authorities to test post-quantum TLS roots and the issuance of ML-DSA-87 certificates. ML-DSA is the signature algorithm standardized by NIST in FIPS 204. In August, Microsoft added seven pilot roots, from ComSign, DigiCert, HARICA, IdenTrust, Sectigo, Shanghai Electronic Certification Authority and SSL.com. These certificates are not publicly trusted: they are only for interoperability testing in closed environments, never in production. Applications remain open until the end of 2026. On the desktop side, Windows 11 has allowed these tests in suitable configurations since the July 28, 2026 updates (KB5101681 for version 26H1, KB5101684 for 25H2). Microsoft warns that ML-DSA support remains limited and evolving.

What to do?

Microsoft recommends six steps:

1. inventory the systems that depend on certificates;
2. map the trust relationships of public and private PKIs;
3. ask vendors about their post-quantum roadmap and testing options;
4. prioritize long-lived equipment, such as embedded systems and OT;
5. set up a test environment separate from production;
6. build a multi-year roadmap, with designated owners and a sequence that takes dependencies into account.

This advice is in line with the coordinated European roadmap, published in June 2025 by member states, with the support of the Commission, within the NIS Cooperation Group, which targets the end of 2030 for high-risk uses.