When will 'Q-Day' arrive? Scientists predict the date when quantum computing will crack all of Earth's digital encryption - with terrifying consequences

As terrifying as it might sound, experts believe the world will soon face a technological crisis that threatens to fundamentally overthrow digital secrecy.

Known as 'Q–Day', this is the moment when quantum computers will crack open all of Earth's digital encryption.

From then, any information not secured by 'post–quantum' protection will be laid bare – including financial transactions and military communications. 

So, when will this world–shattering moment arrive?

The Daily Mail asked six experts on cybersecurity and quantum computing to give their predictions for when Q–Day might arrive.

At the earliest, one scientist suggests that Q–Day could be upon us within two years. 

In contrast, others think it might take decades before quantum computing offers even the slightest threat to the world's digital security. 

While scientists disagree over when Q–Day might arrive, they all agree on one thing – the world needs to start preparing now.

What is Q–Day?

Conventional computer chips, like those in your phone and laptop, use strings of ones and zeros called 'bits' to store and process information.

Quantum computers, meanwhile, exploit the strange properties of matter at very small scales to process information using 'qubits', which can be 'one', 'zero' or both one and zero at the same time.

Essentially, this allows quantum computers to solve multiple problems at once. 

By using specially designed programs, scientists think it might be possible to make computers that are exponentially faster than those relying on conventional chips.

According to some experts, problems that could take literally billions of years to solve on normal computers could be cracked in seconds on quantum computers.

The problem is that this incredible computing power could be turned on all of the encryption that keeps our private information safe.

Although it might not come as one distinct moment, cybersecurity experts call the advent of this new quantum threat 'Q–Day'.

When do the experts believe Q–Day will arrive?

Even the leading experts on the topic aren't entirely sure when it will arrive.

In recent years, companies like Microsoft and Google have made major breakthroughs in quantum computing, but the engineering challenges ahead are immense.

But if rapid advancement comes soon, the end of traditional encryption might arrive sooner than many expect.

Dr Chloe Martindale, senior lecturer in cryptography at the University of Bristol, told the Daily Mail that it could come anywhere in the next 'two to 20 years'.

Even at the later end of that range, the arrival of quantum decryption would be a problem due to something called 'harvest now, decrypt later'.

This is a strategy in which criminals and nation states steal as much encrypted data as they can now in the hope that they can crack it when quantum computing becomes available.

Dr Martindale says: 'A government or company with a sufficiently powerful quantum computer would be able to decrypt and potentially alter anything sent over the internet anywhere in the world.

'But, encrypted data is stored now, and some of it – like medical data – you may also want to be private in 20 years' time.'

This is especially concerning given that several experts and government agencies believe that Q–Day could come sometime in the next five to 10 years.

Jason Soroko, Senior Fellow at Sectigo, told the Daily Mail: 'The biggest misconception is that we will never get there and that quantum computers will never be a threat.

'The current state of engineering is proceeding at a sufficient pace that 2030 is a good chance to see that.'

However, Mr Soroko also points out that we might not necessarily know when Q–Day has arrived.

He adds: 'In the event that a country does develop a quantum computer capable of breaking current encryption methods, it is likely that they would keep it a closely guarded state secret, as the UK did when it broke the Enigma code during World War II.'

Likewise, Ewan Ferguson, CEO of cyber security firm Full Proxy, told the Daily Mail: 'When it will arrive is highly uncertain, and nobody can put a precise date on it responsibly. What we do is plan against credible risk windows.

'The UK’s National Cyber Security Centre (NCSC) has explicitly set an encryption migration timeline to be completed by 2035, with key milestones in 2028 and 2031.

'However, the parallel US authority NIST has suggested that this timeline should be completed earlier, by 2030. So even government experts aren’t aligned.'

This isn't necessarily because the government agencies believe Q–Day will arrive on these dates, but rather because it takes a long time for huge institutions to update their security.

On the other hand, some scientists working directly on the problem of quantum encryption think that the world might have a lot longer.

Professor Artur Ekert, a quantum physicist at the University of Oxford, told the Daily Mail: 'Quantum computers capable of breaking public key crypto systems are probably decades away, but nobody can prove, or give any reliable assurance, that it is the case.'

But even with that much time to prepare, Professor Ekert insists: 'We must start preparing now. For one thing, we need to educate the next generation of cyber warriors in quantum tech.'

However, some experts are not sure that Q–Day is an imminent threat at all.

Professor Robert Young, an expert on quantum encryption from Lancaster University, told the Daily Mail: 'While the science is incredible, the timeline for a cybersecurity apocalypse is often exaggerated.

'Q–Day still feels a long way off. In this field, we often joke that practical quantum computing has been "five years away" for the last 25 years.'

Professor Young added that quantum decryption faces 'significant hurdles' and that he does not believe 'we will see quantum computers used to crack standard cryptography for quite a while yet.'

When quantum computing does arrive, Professor Young doubts that it will be as much of a threat to cybersecurity as many suspect.

Even with quantum computing, the costs and time needed to crack encryption are significant, and states with this technology will have many more profitable uses to focus on.

He adds: 'This technology will not be sitting in a basement; it will be housed in massive, state–controlled facilities. 

'It will likely only be available to major governments, and frankly, intelligence agencies usually have cheaper ways of targeting encryption.'

Likewise, Dr Damiano Abram, a lecturer on cyber security at the University of Edinburgh, told the Daily Mail: 'I do not know when Q–Day could arrive. As a matter of fact, it may also never arrive.'

The issue is that current quantum computers can only handle a small number of qubits at any one time.

The bigger the quantum system in the computer gets, the more chance there is that the quantum particles start to interact with other particles around them.

This could corrupt the information on the computer and affect the accuracy of any results.

'To avoid this, one needs to rely on quantum error correction codes, which essentially "spreads" the information contained in a few qubits over a much larger number of qubits,' says Dr Abram.

'Essentially, we are stuck in a loop: to perform more complex computations, we would need to handle more qubits; to handle more qubits, we need better error correction; to get better error correction, we need to handle more qubits.'

Physicists, engineers and computer scientists might find a way to break this loop one day, but there might also be an absolute physical limit on how big a stable quantum system can get.

Dr Abram adds: 'If that is the case, quantum computers may never reach the scale that poses a threat for cryptography.'

However, the threat of Q–Day is still so significant that governments and companies should still plan with that eventuality in mind.

Dr Abram concludes: 'We need to start using post–quantum cryptography today, even if it is unclear when, and if, quantum computation at scale becomes a thing.'