Free post-quantum scan: will your website withstand quantum computers?

Why talk about it now?

Quantum computers regularly make the headlines, often with alarmist titles. Let us be clear: as of today, no known machine can break the encryption that protects your connections. And yet ANSSI, the European Union, NIST and the G7 are all calling for action now.

There are two reasons for this. Some data stolen today can be decrypted tomorrow. And changing an organisation’s cryptography takes years: ANSSI estimates that the transition will last more than a decade and touch the entire digital ecosystem.

Estimates are tightening too. In 2019, breaking a 2048-bit RSA key was thought to require around 20 million qubits. In May 2025, Google researcher Craig Gidney showed that fewer than a million noisy qubits could be enough, in less than a week. That is still very far from existing machines, but the gap is closing from both ends.

“Harvest now, decrypt later”

This is why the threat is already real. A patient adversary, typically an intelligence service or an APTAPT (advanced persistent threat)A highly organised group of attackers, often linked to a state, that quietly gains long-term access to a targeted network to spy, steal secrets or prepare sabotage. group, can record encrypted communications it cannot read today and store them. The day it has a quantum computer, it breaks the key exchange and reads everything.

To find out whether this concerns you, ask three questions. How long must your data stay secret (medical records, contracts, trade secrets, research)? How long will it take you to migrate your systems? When could a relevant quantum computer appear? If the secrecy period plus the migration time goes beyond the third date, you are already late.

What falls, and what holds

A quantum computer does not break everything. Shor’s algorithm targets public-key cryptography, which protects the key exchange of every TLSTLS (HTTPS)A protocol that encrypts and authenticates exchanges between two machines, such as your browser and an HTTPS website, so that data cannot be read or altered in transit. connection and signatures. Symmetric encryptionEncryptionA process that makes data unreadable to anyone who does not hold the right key, to protect its confidentiality while it is stored or transmitted. and hashingHashing (and salting)A calculation that turns any piece of data into a fixed-size fingerprint that cannot practically be reversed, and that changes completely if the data changes even slightly. fare much better.

The answers exist: on 13 August 2024, NIST published its first three standards, ML-KEM for key exchange, ML-DSA and SLH-DSA for signatures. They are recent, and so is their cryptanalysis: in 2022, the SIKE algorithm, still in the running in the NIST competition, was broken in under an hour on an ordinary classical processor.

This is why ANSSI recommends hybridisation: combining a post-quantum algorithm with a proven classical one. If one falls, the other still protects.

Your visitors are ready, is your server?

Good news: the transition has already begun. Since Chrome 131, in late 2024, browsers have offered the standardised hybrid exchange, called X25519MLKEM768. It combines X25519, a classical elliptic curve, with ML-KEM-768. To read the conversation, an attacker would have to break both.

Servers lag well behind: Cloudflare estimates that around 10% of its customers’ origin servers support this exchange. A browser can therefore offer it without your website accepting it, and nothing tells you so. That is exactly what the scan checks.

What the free scan measures

KrakenShield’s post-quantum scan opens a few TLS connections, offering what a current browser offers, reads the server’s first answer and stops there. It tests no vulnerability and changes nothing. It works on any public website: yours, a customer’s, a supplier’s.

You get a score out of 100 and a level: ready from 85, partial from 50 to 84, exposed below 50. Without a hybrid exchange, a website tops out at 40, even if the rest of its setup is perfect. Do not take this as a reproach: it is the case of many servers today, and it shows where to start.

The scan also reports what the score does not say: a firewall or load balancer that leaves an oversized negotiation message unanswered, an old version of the exchange dropped by browsers, an expired certificate. The result downloads as a PDF, to pass on to your provider or your management.

One limit, in all honesty: the score covers the visitor’s connection to the first server met. It says nothing about what happens behind that server, nor about the rest of the site’s security.

Your score is low: what next?

1. Move to a recent TLS library. According to ANSSI, OpenSSL has implemented the hybrid exchange since version 3.5.0. On many servers, an operating system upgrade is what brings it: plan a backup and a time slot.
2. Put the hybrid exchange first in the group list, keeping the classical groups behind it for older clients. On nginx: ssl_ecdh_curve X25519MLKEM768:X25519:secp256r1;. On Apache: SSLOpenSSLConfCmd Curves X25519MLKEM768:X25519:prime256v1.
3. Check the equipment in front of the server. The hybrid message spans two network packets: old firewalls or load balancers can block it.
4. If your website sits behind a CDN, look at its settings. With a free account, KrakenShield can apply TLS 1.3 and HSTS on Cloudflare with your own token, with tracked and reversible changes.
5. Run the scan again. Check that the score has moved, on each of your domains.

The timeline to keep in mind

The European roadmap also invites entities covered by the NIS 2 directive to include the quantum threat in their risk management, at board level.

Beyond the website

The scan gives you a first figure, not a programme. For what comes next, appoint a lead and inform management, inventory your cryptography (VPN, SSH, e-mail, code signing, business applications), classify your data by how long it must stay confidential, and ask each supplier for a roadmap. Chapter 9 of Cyber from A to Z details this approach, with Belinda.

So, should you worry? No. Should you get started? Yes, and the sooner the cheaper. Start by measuring: your post-quantum score is one click away, free of charge and without an account.