How can you keep your data private when quantum computers arrive? I’m a cryptographer working to solve this, AMA!

[u/FUTURES_2026]

Hi r/IAmA, I’m Chloe Martindale, a researcher in cryptography – the development and use of mathematics to make and break encryption algorithms that protect our information online, from the messages we send to the data we want to keep private.

My research focuses on combating an emerging problem: quantum computers could soon break the mathematical status that today’s encryption relies on. So the algorithms we use to protect our data will need to change.

That means developing and testing new algorithms. A central element of my research is trying to find weaknesses: if a supposedly secure mathematical problem turns out to be easier to solve than we thought, we need to know now rather than when everyone is relying on it.

Ask me anything about:

• How encryption keeps your data private
• What quantum computers could mean for online security
• Why we need new forms of encryption
• How you test an algorithm to find out whether it is secure
• Whether your online data is really private
• What the future of internet security might look like

Thanks to all of you who've asked questions so far and those of you who've been reading along. I will be checking back for more questions periodically for the next week so keep your questions coming! You don’t need to know any maths or computer science to take part, I’m happy to explain the ideas from the ground up.

AMA!

[u/Edman70]

For years, I've believed that quantum computing would land in the wrong hands before anyone in charge in crypto-land made the meaningful changes, and as such, it would all be worthless overnight.

At this point, do you believe this is a real threat, and how soon?

[u/FUTURES_2026 → u/Edman70]

Some meaningful changes have already happened - there is now standardized cryptography that we don't think can be broken by quantum computers and it is starting to be deployed on a global scale. However, there is still along way to go! Most communication is still protected using "classical" cryptography that can be broken by a quantum computer, but there is now a serious effort to change that and I am hopeful that we will have transitioned most things before the day that a quantum computer that can run these devastating algorithms arrives.

[u/Edman70 → u/FUTURES_2026]

Thank you, Ms. Martindale. I hope you're right!

[u/AccessibleTech]

Can blockchains protect themselves from quantum computer attacks by switching to quantum-resistant (post-quantum) cryptographic algorithms?

How much quantum computing power would it take to break the cryptography blockchains use today, and does any quantum computer have that much power now?

How much energy would that attack use?

[u/FUTURES_2026 → u/AccessibleTech]

Different blockchain companies and applications all use vastly different algorithms so this has quite a complicated answer! Some blockchain implementations are already using algorithms that we don't know how to attack using quantum computers. For example any blockchain technology based on Fully Homomorphic Encryption such as Zama is currently believed to be unassailable by quantum computers. In principle it wouldn't be too hard to move across all blockchain technology to quantum-safe alternatives, but it's up to the individual companies to do so.

To break the blockchains in use today that aren't using quantum-safe cryptography, you would need 400-800 logical quantum bits (qubits) to attack these algorithms, depending on how they're set up, which is still a long way off. A logical qubit refers to the smallest part of a quantum computer that can perform arithmetic operations, and we can now create a logical qubit but this is fairly new (2024), and the record is still a computer with 1 logical qubit! However, to run any interesting quantum algorithm for breaking cryptography we need to entangle at least 400 logical qubits, so we've got a bit of time.

On the amount of energy that would use, we don't really know yet because we haven't figure out how to do it, but it would certainly use a huge amount of energy. One of the main engineering challenges with building quantum computers is keeping the machine as cold as possible (as close to 0K as possible), which of course uses huge amounts of energy.

[u/knbknb]

Do you think learners can get deep understanding of quantum phenomena (q-computing, q-cryptography) without at least some Physics background?

This is my impression:

There are two ways to learn about quantum computing: From Physics or not from Physics (e.g., from Computer-Science, Maths, or Popular Science).

People in the first category learned how quantum phyics is differnt from Classical Physics, Particle Physics

People in the second category can try to enter the field from a "higher level" of learning, peraps without any Physics underpinnings (just math and innovative teaching materials)

Which resources of the latter type can you recommend?

[u/FUTURES_2026 → u/knbknb]

For people from a computer science or maths background, I think that quantum information theory is a really good way into getting an understanding of quantum algorithms. It allows you to reason about quantum computing building on a set of formal principles, which is the same style of reasoning that is used across maths and computer science. You can even implement "quantum circuits" on your laptop in programs that will give you an estimate of how this would run on a quantum computer in terms of quantum memory and time. IBM has some great open source resources for learning about quantum algorithms, and for implementing quantum circuits for breaking cryptography, I recommend looking at Qarton.

[u/agasabellaba]

Alright I'm gonna ask it - is our online data really private?

[u/FUTURES_2026 → u/agasabellaba]

A lot of it is not, and a lot of it is private against your average hacker but not necessarily against someone with state-level powers. But there are ways of protecting your data even from state-level powers - things like using Signal to communicate and DuckDuckGo for searches. Even then some information can be leaked sometimes, but it's better than leaking everything.

That said, there are multiple reasons to care about private data: personal privacy but also things like online banking, online shopping, or healthcare information. In these kinds of situations there is "hidden" cryptography protecting really sensitive data that is shared over the internet - which we don't really see but which we are relying on. These algorithms have far fewer weak points as they are set up with privacy as a first concern rather than an afterthought.

[u/Sciros]

We've had the luxury of an algorithm going unbroken for multiple decades now in RSA. Do you anticipate PQ algorithms to have anywhere near that staying power, or do you see them as something that will need replacement every couple of years? How "special" are Shor's and Grover's algorithms in that respect?

[u/FUTURES_2026 → u/Sciros]

The algorithms that have already been standardized are now about 20 years old, so that shows quite some maturity. Personally I think that the biggest threat is going to new quantum algorithms as people get to play around with quantum computers and see what they can do: the difference between writing down with pen and paper in the 50s what you think a computer might be able to do vs. playing around with one now is huge - and the same could apply to quantum computers.

I guess the short answer is "I don't know", but I'm definitely glad that there is effort to standardize multiple fundamentally different algorithms so that we have alternatives if standards get broken.

Shor's and Grover's algorithms are very special and only apply to quite narrow scenarios, but so far there haven't been many new ideas for quantum algorithms to apply to cryptography (Kuperberg's algorithm is possibly an exception, but that is at least inspired by Shor). But this still comes with the disclaimer of above: at the moment all we can do is argue theoretically, which is very different from playing around with the actual machines.

[u/jpg_lady]

how soon is soon?

[u/stockshelver → u/jpg_lady]

Within a day or so of all those cures for cancer

[u/FUTURES_2026 → u/stockshelver]

Unfortunately breaking cryptography is a lot more realistic than curing cancer at the moment :(

[u/FUTURES_2026 → u/jpg_lady]

It's really hard to say with certainty: it could be a year or it could be 20 years. The trouble is that changing every cryptographic algorithm on every device in the world - and carefully checking for security problems - takes a really long time! The fallout of being prepared is so high that it's better to be safe than sorry.

[u/ST-Fish → u/FUTURES_2026]

What would have to happen for it to get done in 1 year?

[u/FUTURES_2026 → u/ST-Fish]

The major engineering hurdle that still remains is figuring out how to entangle 2 logical qubits. (A logical qubit is a collection of quantum bits that together can be used for arithmetic operations to build a circuit). If someone has a breakthrough with entanglement in the next year, I would not be surprised if the scaling follows shortly after.

[u/translunainjection]

How do we keep our data private when every tech platform is a monopolistic data harvester and your friends refuse to use the privacy-respecting alternative (if you’re lucky enough to have one) because it has 10% more friction?

[u/FUTURES_2026 → u/translunainjection]

Great question - that's definitely a tricky one! There's no way that I know of keeping your data private if for example you choose to use Messenger. The only real alternative is to use alternatives when you can - but it does come at the cost of not being able to keep in contact with friends who don't want to use those alternatives.

[u/HGrande]

I imagine you'd have to “fight fire with fire” and the encryption/decryption would have to move to quantum computers, but what does that do to performance and data in transit if you’re still on your non quantum laptop?

[u/FUTURES_2026 → u/HGrande]

We actually don't! We can encrypt our data now on current machines - even legacy devices - using cryptography based on maths that quantum computers can't crack. Quantum computers are really good at a handful of things, but most algorithms run just as slowly on a quantum computer as a current one. A lot of these new algorithms are in fact already standardized and deployed, so depending on your browser you might be using one right now :)

[u/PositiveHabit3343]

do you think there will be a period where the old encryption is broken but the new quantum-resistant stuff is not rolled out yet? like a gap where everything is just exposed for a while

[u/JoeyBigtimes → u/PositiveHabit3343]

Yeah. We’re living in it.

[u/FUTURES_2026 → u/JoeyBigtimes]

We could be! But I don't think so, just because the most likely secret quantum computers would be held by powerful governments who are not yet demonstrating the ability to decrypt all the military communications of their enemies.

[u/FUTURES_2026 → u/PositiveHabit3343]

I think it's likely that some encryption is not updated in time. Governments which have the capacity to work on this are prioritizing "critical national infrastructure": things like water, electricity, internet, banking, or travel networks. But I would expect that there will be large parts of the world that don't have the capacity to transition even their critical national infrastructure.

[u/xkrysis]

What are we looking at timeline wise until quantum computing starts to be able to break old/deprecated key lengths? Then what is the gap before it catches up to modern higher key lengths? Is there a period of time where we can run ahead by increasing key lengths?

[u/FUTURES_2026 → u/xkrysis]

It's hard to say exactly. Even to break old/deprecated key lengths we need 100s of logical qubits (an arithmetic circuit made of quantum bits), and at the moment the record is 1. However, the gap is basically zero. It is even likely that every key length gets broken at the same time. The modern key lengths are designed to be secure against algorithms which get exponentially worse with the size of the key, but the quantum algorithm for this just scales with the key so we don't have a big difference in how effective the algorithm is for different key sizes.

[u/FUTURES_2026]

This Ask Me Anything is part of FUTURES: A Festival of Discovery, delivered by the universities of Bristol, Bath and Bath Spa. FUTURES is part of European Researchers’ Night, a pan-European event Night taking place in 40 countries and more than 460 cities all over Europe and beyond simultaneously, funded by the European Union to bring science and society closer and heighten young people’s interest in science. FUTURES 2026-27 is funded by the European Union under the Marie Sklodowska Curie Actions, Grant Number 101305354. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union. Neither the European Union nor the granting authority can be held responsible for them.

[u/Media_Browser]

Have you ever been asked to spell your name backwards ?

[u/FUTURES_2026 → u/Media_Browser]

Not recently. Maybe when I was a teenager? E O L H C

[u/Media_Browser → u/FUTURES_2026]

Sorry no short cuts especially with such a nice long surname that what makes it challenging .