Whether preventing somebody from intercepting your credit card details, verifying somebody's identity, or enabling Bitcoin, cryptography provides the underlying security that enables much of our digital lives today. However, current-day cryptography is on a precipice as the advent of quantum computing threatens to undermine how we protect our information. This article looks at quantum computing, what it means for encryption, and what organisations should do about it.

(N.B. Cryptography is one of those subjects that can quite quickly delve into maths that is well beyond me, so this isn't going to be an in-depth guide.)

How does encryption work?

Encryption works by using mathematical techniques to transform data into a format that can only be read by someone with the correct decryption key. A key concept in encryption is the use of one-way functions — mathematical problems that are easy to compute in one direction but extremely difficult to reverse without specific information.

For example, multiplying two large prime numbers together is straightforward, but determining the original prime numbers from their product (a process known as factorisation) is extremely challenging for classical computers. If we take the primes 53 and 61, their product is 3,233. While anyone can multiply these numbers quickly, figuring out that 53 and 61 are the factors of 3,233 without prior knowledge requires significant computational effort. This calculation becomes more difficult as the numbers get bigger; to the point that it can take years or even decades to find the answer.

This asymmetry forms the basis of many encryption methods, ensuring data remains secure as long as the original key or factors are kept private.

So one-way functions aren't actually one way?

Correct. A one-way function can be undone; it's just very difficult. The question is, how long would it take to undo it? This, amongst other factors, gives rise to what is known as a 'cover period'. That is to say that when encrypting information that needs to be kept secret, you should consider how long it needs to stay secret for.

Imagine the scenario where battle plans need to be shared in secret to stop the enemy from countering them. Those plans only need to remain secret until the battle has taken place, whereupon it will become quite obvious what was being planned. The battle planners, when encrypting their information, should consider whether their codes could be broken while they are planning the battle.

We can, and should, apply this concept in the digital world, but there is also the added complexity that computers have been getting faster in line with Moore's Law. This means that one-way functions which might have taken decades to solve at one point could only take years, or weeks, in the future; so we have to design our cryptographic methods in anticipation of what technology advancements might happen in the future.

Enter quantum computing

Quantum computing is a nascent form of computing that uses the principles of quantum mechanics to process information in ways that classical computers cannot. Unlike conventional computers, which use bits as the smallest unit of data (representing either 0 or 1), quantum computers use quantum bits, or qubits, which can exist in multiple states simultaneously due to a property called superposition. This allows quantum computers to perform complex calculations at speeds exponentially faster than traditional computers — and that includes solving many of the problems relied upon by encryption today. This is a different order of change from the rapid, but gradual, advancement of computing that we've seen over the last 100 years or so — and if we are to keep our information secure, our approach needs to change just as sharply.

Quantum computers are still early in their development, but some are projecting they will have practical applications within the next 5 years, though it is also estimated that it will be around 10 years until they can be used to break modern-day cryptography.

Enter post-quantum cryptography (PQC)

In 2016, NIST launched a competition to standardise post-quantum cryptographic algorithms (that is to say, cryptographic algorithms which, in theory, cannot be easily broken by quantum computers), bringing together the world's leading cryptographers to develop and validate new encryption methods. After several rounds of rigorous evaluation, in 2024, NIST finalised the first set of quantum-resistant algorithms that will become the new standards for digital security in the quantum era. In March 2025, the NCSC published guidance and a timeline for the migration to post-quantum cryptography. It sets out three key milestone dates:

The NCSC has taken an important step by defining a timeline for PQC adoption; this sends a clear message to suppliers and developers that PQC is coming and will become the norm. It sets an overall direction for an industry. I would argue, however, that while there is a huge amount of work to be done, time is short and a more aggressive timescale is needed.

10 years is a long time away. Why worry now?

Two reasons.

Encryption doesn't stop somebody getting their hands on your encrypted data. It just stops them being able to make sense of the information that they have access to. What if somebody got a copy of your message and held onto it until a quantum computer became available? Somebody decrypting your secret information in 10 years' time might not be a concern, but what if you needed a cover period of 15 years? It feels like a long way out, but next year we'll only have 9 years to play with, then 8, then 7 — you get the idea. As the time gets closer, the issue becomes more acute.

A move to post-quantum cryptography is going to be highly complex, time-consuming, and potentially expensive. Particularly in the Operational Technology space, where systems might not be able to be upgraded to support PQC, replacing technology (or accepting security risks) might be the only option.

The NCSC guidance does a really good job explaining the steps that organisations will need to go through, so I won't try to come up with my own methodology, but the amount of work involved in completing those steps will vary enormously. My theory is that the organisations most at risk (the likes of Critical National Infrastructure, Government, Financial Services) will have the hardest time making the switch.

My call to action

For me, migration to post-quantum cryptography has echoes of the millennium bug. We know that quantum computing is coming. We know that it has the potential to be hugely disruptive (but also exciting, for reasons beyond security). We know what needs to be done about it. We have enough of a head start to avoid the doomsday scenario. So, my call to action:

  1. Start now. Review the actions and timelines set out by NCSC. Don't sit on your hands assuming that you've got 10 years before this becomes an issue. Depending on your security requirements, it could already be an issue for you.
  2. Build an inventory of where cryptography is used across your organisation and work with suppliers and developers to understand what would need to happen to adopt PQC.
  3. Build PQC requirements into solutions now, whether you are procuring them or building them yourself. It will be far more cost-effective and less burdensome to build these requirements into existing technology strategies, deployments, and procurements than to stand up dedicated PQC migration programmes (even though they will inevitably be required).