A Quantum Computing graduate student has calculated how large a quantum computer would need to be in order to crack Bitcoin’s secure cryptographic algorithm. 

Mark Webber and his colleagues from the Ion Quantum Technology Group at the University of Sussex concluded that quantum computers need to be a million times larger than they currently are before ever cracking Bitcoin’s SHA-256 algorithm – an algorithm first published by the U.S. National Security Agency (NSA) in the early 2000s. 

The Ion Quantum Technology Group conducts research around quantum computing and microwave quantum sensors. 

Conventional wisdom maintains that Bitcoin’s encryption technology is so strong that attackers need to commandeer 51% of the combined computing power of the global Bitcoin network to compromise its “immutable” ledger. 


But every transaction on Bitcoin’s ledger is assigned a cryptographic key – a random string of letters and numbers – which is vulnerable for a finite length of time. 

Given enough computing power – or a powerful enough quantum computer – this key can be cracked. 

Webber estimates that if an attacker has a ten-minute window to crack the key, they would need a quantum computer with 1.9 billion cubits. If the key is vulnerable for 24 hours, this figure drops to 13 million qubits. 

Could quantum computers ever crack Bitcoin?

Given that the largest superconducting quantum computer on the market is IBM’s 127 qubit model, it doesn’t look like quantum computers pose much of a security threat to crypto. 


In traditional computing, Moore’s Law dictates that the number of transistors in a microchip doubles every two years, while the cost of the computers is halved. 

In essence: as time rolls on, we get more bang for less buck. 

In the world of quantum computing, this law has been replaced by Neven’s Law, which dictates that quantum computing power undergoes "doubly exponential growth relative to conventional computing". 

To put that into perspective, doubly exponential growth would have given us laptops and smartphones back in 1975

So, if quantum computing hardware improves exponentially faster than regular transistor circuits, then theoretically it could one day eventually crack Bitcoin’s code. 

It’s just a question of when. 

Webber believes it might be possible in a decade

Daily Debrief Newsletter

Start every day with the top news stories right now, plus original features, a podcast, videos and more.