Post quantum key exchange

What is actually turned on

The nginx build compiles against OpenSSL 3.5, which carries ML-KEM, the standardized post quantum key encapsulation mechanism. The TLS snippet the manager ships offers X25519MLKEM768 first, with the classic curves behind it.

ssl_ecdh_curve X25519MLKEM768:X25519:prime256v1:secp384r1;

A browser that supports the hybrid group uses it. One that does not falls back to a classic curve and connects exactly as before. Nothing breaks for older clients and nobody has to know to ask for the newer behavior.

Why it is hybrid

X25519MLKEM768 combines a classical elliptic curve exchange with ML-KEM. Both have to be broken for the session key to be recovered. That matters because ML-KEM is newer and has had less time under attack than X25519 has. Pairing them means adopting the new one costs you nothing even in the unlikely case it turns out to have a weakness.

Who this actually matters to

• Anything with a long secrecy lifetime. Medical records, legal documents, personal data, source code. If it still matters in fifteen years, it matters now.
• Anybody whose traffic crosses networks they do not control, which is everybody serving the public internet.
• Organizations with a compliance timetable. Several national bodies have published migration dates, and being able to say the edge already does this is worth having.

It matters much less for something that is public anyway, or that stops being sensitive within a week. Being honest about that is more useful than pretending everything is urgent.

How this compares

On the comparison page this is one of the rows where we come out ahead, and the reason is not cleverness, it is that we build our own TLS stack.

Building our own TLS stack is a cost in almost every other row of that table. It buys this one.

Checking your own build

The dashboard puts a post quantum ready badge next to the OpenSSL version when the build supports it. From a terminal you can confirm it directly:

openssl list -kem-algorithms | grep -i mlkem
nginx -V 2>&1 | tr ' ' '\n' | grep -i openssl

Common questions