Q-Day is coming!

Imagine a world where the technology that keeps our information safe as it travels across the internet stops working. Suddenly your internet banking, intimate WhatsApps and passwords saved in website databases become accessible to attackers.

# I’ve Got the Key, I’ve Got the Secret

Today we all rely on a technology called Transport Layer Security (TLS), which allows a secure, encrypted channel to be created between two parties on the internet – e.g. you and your bank’s website. We can tell when TLS is working because there is usually a “padlock” sign next to the address in our browser address bar.

We’ve all played with Caesar Ciphers as children – where you write a message out but shift each letter a specific number of letters ahead or behind in the alphabet.

So “HELLO” shifted by 1 become “IFMMP”.

I wrote about it here. Your recipient is told the number of letters to shift forwards or back and they can decrypt the message. This information (i.e. the number of letters to shift) is called a “key”. The key above is “1”.

Having the same key to encrypt and decrypt is dangerous on the internet because before your bank sent you a balance update it would need to tell you how to decrypt that information – and anyone listening on the connection could see that key and use it to decrypt the balance information. The encryption becomes useless.

At the heart of TLS is a technology called Public Key Infrastructure, PKI. PKI uses an extremely clever bit of mathematics that allows an encryption key to be split into two parts. Lets call them Key A and Key B. When Key A encrypts data only Key B can decrypt it.

When you navigate to a secure website, the website sends you its Key A (but keeps its Key B, this is important!), and you use that to encrypt information on your computer or smartphone, and this is then sent to the website that uses its Key B to decrypt the information. The data is “secure” as it travels across the internet. Even if an attacker got hold of a Key A, all they could do was use it to encrypt data, not read encrypted information.

Clever, right?

The technical term for these keys are public and private keys. A Public Key can be handed out freely for other parties to encrypt data and we keep our Private Key very secure, usually in a Hardware Security Module or Secure Enclave.


The technology industry is in a constant arms-race with highly-funded, often nation-state-backed hacking organisations.

These ne’er-do-wells try and “crack” (guess) private keys using ever more powerful computers. This is called a Brute Force attack – guessing billions of combinations of 1s and 0s to try and discover the private key. This would give them access to encrypted data that they continually slurp up off the internet.

The more powerful computers get, the more guesses-per-second attackers can make of your private key

The mathematics behind generating public/private key pairs is based on factorising the prime numbers of an integer. If you’re not a maths geek, don’t worry, you don’t need to know what that means.

But there is a new technology on the horizon called Quantum Computing, and this has the potential to make our existing cryptography useless.

IBM’s System One quantum computer

In 1994, American mathematician Peter Shor developed an algorithm that theoretically could crack public key cryptography in fractions of the time of conventional computers. Shor’s algorithm has since been used to demonstrate factorisation of large integers is possible, although current Quantum technology has limitations, specifically around quantum noise and accumulating errors.

But if (when) this technology stabilised, it can be used to find the private key for a piece of data that has been encrypted by a public key. Scary stuff.

The moment in time that this becomes possible has been called, Q-Day. (I’m sure Netflix has a movie in the works already).

Q-Day isn’t going to happen soon, the technology doesn’t exist yet. Finding private keys for RSA2048 encrypted data requires a billion “qubits” (quantum bits) but even our most powerful quantum computers only have 400 qubits. IBM has published its Quantum roadmap which shows that a Quantum equivalent to Moore’s law might be starting.

Adopting Quantum-Resistant Cryptography Today

I mentioned before that hackers are already grabbing as much encrypted data as they can so that when Q-Day eventually happens, they can start decrypting that data. This means we’re already too late to protect a lot of the encrypted data that has passed across the internet and into the hands of nation-state hackers, but we can take steps to prevent future encrypted data from being susceptible to Quantum decryption.

The sooner we all switch to Post-Quantum-Cryptography (PQC) the less stored, encrypted data will be decryptable in the future.

We owe it to ourselves and our customers to take action NOW!

In 2022, the US National Institute of Science and Technology (NIST) ran a competition to find quantum-resistant cryptographic algorithms with CRYSTALS-KYBER emerging as the PKI winner, and NIST recommendation.

CRYSTALS-KYBER is a “Lattice-based” PKI algorithm, a mathematical problem which is likely to be intractable even to Quantum algorithms, based on our current understanding.

But it must be really hard to switch from existing encryption to CRYSTALS-KYBER, right?

Wrong! Many of the leading encryption libraries already support them. OpenSSL from v3.2 onwards supports Post-Quantum (PQ) algorithms, this library is used by a very large number of public websites that run on Linux servers/containers. Switching is usually a simple configuration change (don’t test this one in production, folks).

Other implementations include Bouncycastle, a favoured Java and .NET crypto library, Google’s BoringSSL, and WolfSSL.

What About My WhatsApps??!

While I’m sure you don’t send anything potentially damaging via WhatsApp, you can rest assured that WhatsApp and Signal both use Quantum-Resistant cryptography. They both use the Signal Protocol which added Post-Quantum Extended Diffie Hellman (PQXDH) in September 2023.


Q-Day is likely to be decades away, but breakthrough discoveries and innovations do happen in science that can compress expected timelines. Just look at how Transformers in machine learning accelerated our path to generative AI.

Like AI, Quantum Computing requires a unique blend of extreme mathematical genius, technological capabilities and, possibly the most effective restriction, lots and lots of cash.

But that doesn’t mean we have to sit and wait. Malicious actors are storing vast quantities of data today that is encrypted using algorithms which are vulnerable to Quantum attack. Everyone across tech needs to start moving to Post Quantum Cryptography (PQC) as soon as possible to minimise the impact of Q-Day.

Now you know the risk and the solution, it’s time to take action.