Post-Quantum Server Test
This free tool runs a real post-quantum TLS handshake against any public HTTPS server and reports whether it supports quantum-safe key exchange — X25519 + ML-KEM-768. The hostname you submit is used only to run this one check — nothing is stored.
Public HTTPS hosts only, port 443. Enter a domain or subdomain like example.com — no https:// needed.
What this test checks
TLS — the padlock on every HTTPS site — starts with a key exchange: the
browser and server agree on a secret that encrypts the session. Classical key exchange (X25519, ECDH
P-256) is safe against today’s computers but breakable by a future quantum computer. A
post-quantum hybrid group — today X25519MLKEM768, combining classical
X25519 with the NIST-standardised ML-KEM-768 (formerly Kyber) — stays secure against
both. This tool tells you whether the server you entered accepts that group. It does not test
certificates, signatures, or data at rest.
Why it matters: “harvest now, decrypt later”
An attacker doesn’t need a quantum computer today. They can record encrypted traffic now and store it until one exists, then decrypt it retroactively. Anything with a long shelf life — health records, legal files, credentials, IP — is at risk the moment it crosses a classical-only connection. Post-quantum key exchange closes that window before the threat arrives.
FAQ
A host came back “not quantum-safe” — is it broken or insecure?
No. It means that server isn’t offering post-quantum key exchange yet. The connection is still encrypted and safe against today’s computers; it’s just not future-proofed against “harvest now, decrypt later.” Most of the web is still in this state and rolling PQC out gradually.
What can I test?
Any public host that serves HTTPS on port 443 — a domain or a subdomain (e.g. example.com or www.example.com). No path needed. Private, internal, or non-public addresses are refused for safety.
How does it work?
A small server-side prober opens a TLS 1.3 connection to the host on port 443, offering only the post-quantum group X25519MLKEM768. If the server accepts it, the site supports post-quantum key exchange; if not, the handshake is refused. It’s a real handshake — not a lookup or a guess.
What is ML-KEM / Kyber?
ML-KEM (Module-Lattice Key Encapsulation Mechanism) is the NIST-standardised post-quantum key exchange algorithm, published as FIPS 203. It was known as Kyber during standardisation. Servers deploy it in hybrid mode — combined with classical X25519 — so a connection is never weaker than before.