Post-quantum cryptography has stopped being a research topic. OpenSSL 3.5 ships native support for NIST's ML-KEM, ML-DSA and SLH-DSA, and changes the TLS key exchange default to the hybrid post-quantum group X25519MLKEM768. Any TLS connection between two endpoints running OpenSSL 3.5 negotiates a post-quantum key exchange with no explicit configuration from the administrator.

It's Already in Real Traffic

This isn't a spec-sheet capability. Chrome has enabled the hybrid group by default since version 124 (April 2024), and Cloudflare's transparency reporting puts it at roughly 30% of TLS 1.3 connections. A large share of your visitors already arrive PQC-capable — whether that capability gets used depends entirely on your side.

Why Now Rather Than Later

The reason is "harvest now, decrypt later": an attacker records encrypted traffic today and decrypts it once quantum hardware matures. For anything that must stay confidential for years, the threat exists today. The hybrid design is deliberately pragmatic — it combines classical X25519 with post-quantum ML-KEM-768, so the session stays secure as long as either one holds. That makes switching now a low-risk move.

Rolling It Out on a VPS

  • Check your version first: openssl version. 3.5 is the current LTS branch, supported through April 2030; anything older has no native PQC.
  • Let the distro give you 3.5: Ubuntu 26.04 LTS already ships OpenSSL with post-quantum support, which is the low-effort path. Hand-compiling on an old release means maintaining it yourself and rarely pays off.
  • Confirm Nginx links the new library: nginx -V shows the OpenSSL it was built against — then verify the runtime shared library is also 3.5. Mismatches are common.
  • Verify with a real handshake: run openssl s_client -connect yourdomain:443 -groups X25519MLKEM768. It counts only if the handshake succeeds and negotiates that group.
  • Enable hybrid, not pure PQC: standalone post-quantum algorithms haven't accumulated the same field-testing record. Hybrid is the sound choice today.
  • Expect larger handshakes: ML-KEM key material is considerably bigger than elliptic-curve equivalents, so handshakes can slow down on lossy links. Measure before you commit.

Managed Platforms vs Your Own Server

PQC is a textbook example of an upgrade you can only drive if you own the TLS termination layer. On shared hosting or a closed managed platform, you wait for the provider's roadmap. On your own VPS, upgrading the OS, moving to a newer OpenSSL, adjusting Nginx's ssl_conf_command and verifying the handshake are all on your schedule. SharkCloud offers dedicated instances with root access across multiple regions, so you can lead on infrastructure upgrades like this instead of queueing for them.