The quantum threat to your data and our race to stop it

Professor Craig Costello, QUT School of Computer Science

What are the two prime factors of the number 731?

If that question made you pause, you're not alone. Most people wouldn’t solve it on the spot.

But what if it was a different question: 17 × 43?

You might have been able to come up with the answer a little faster (perhaps after grabbing a pen and paper, mentally teleporting back to your grade 5 classroom, writing the numbers on top of each other and scribbling some workings for a moment).

That’s the twist: both questions involve the same numbers. One direction, multiplying 17 and 43 to get 731, is easy. The other direction, figuring out which two primes multiply to give 731, is much harder, especially as the numbers get bigger.

This simple mismatch in difficulty lies at the heart of modern cryptography.

For decades, cryptographers have relied on exactly this kind of mathematical one-way street.

We’ve built systems that let honest users quickly scramble (encrypt) their messages using fast operations like multiplication, while making it nearly impossible for attackers to unscramble (decrypt) them without the key – because doing so would require solving problems like factoring enormous numbers (much, much bigger than 731).

This principle is what secures your private information online.

The next time you’re doing internet banking or shopping online, look for the little padlock icon in your browser’s address bar. That padlock tells you your connection is encrypted.

And the math behind it? It traces back to exactly the same problem you started with: turning 731 back into 17 and 43, but with numbers hundreds of digits long.

Now here’s the good news: with today’s classical computers, even if every machine on the planet teamed up and worked for the entire lifespan of the universe, they still wouldn’t be able to crack the large numbers used in modern encryption. That’s why, when implemented properly, that padlock really does protect your data.

These new systems must be fast, efficient and airtight. They need to protect everything from your text messages to your health records to national secrets – before quantum computers arrive on the scene.

It’s a thrilling time in cryptography. We’re witnessing the largest migration of cryptographic infrastructure in history.

Governments, tech companies, and researchers are all racing to test and deploy new post-quantum algorithms. It's like swapping the engine on a moving car… except the road is the internet, the passengers are billions of users, and the stakes are your privacy, security and trust.

So, the next time you see that padlock in your browser, remember, there’s a world of mathematics working behind the scenes to protect you.

And as we move toward a quantum future, researchers are working to ensure that padlock stays locked – for good.

Want to learn more? Explore our Master of Cyber Security.