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Is Quantum Computing Actually A Threat To Bitcoin?

Is Quantum Computing Actually A Threat To Bitcoin?

Explainers Cryptocurrencies

12 Mar 2021

An impressive number of hoaxes and urban legends have emerged around quantum computing . Our imagination is a powerful enough tool to make us believe in Loch Ness Monsters dragging people underwater, the rise of artificial intelligence exhibiting human traits and now a mystic quantum algorithm that can wipe Bitcoin off the face of the earth.

So, what is quantum computing? Does it really pose a threat to Bitcoin, and can it ultimately deprive the digital gold of its value?

What is quantum computing?

Quantum computing is an emerging science branch that uses quantum phenomena, such as superposition and entanglement, to solve difficult mathematical problems. In 2019, Google said, it’s built a machine that’s reached “quantum supremacy” by spending only 200 seconds for solving a task that would take the fastest supercomputers about 10,000 years. Chinese scientists from the University of Science and Technology in Hefei developed a machine that is rumoured to solve the boson sampling problem in as little as 200 seconds, which would take a regular, however, very fast supercomputer TaihuLight about 2.5 billion years.

Now, what are these superposition and entanglement concepts? And what impact can they ultimately have on the security of the Bitcoin Network?


Superposition is the ability of a quantum system to be in multiple states at the same time: “here” and “there,” “up” and “down”, “1” and “0”, and — yes, this has something to do with Bitcoin mining.

In Bitcoin mining, computers have to solve a mathematical problem of searching for the smallest 32-bit nonce possible until a satisfactory solution is found.

To find this nonce with a regular, however powerful, mining setup, you have to pump a lot of energy. But quantum computers, in theory, can solve such a problem in a matter of seconds without too much energy spent.

That is because, in contrast to regular bits that can only be 1 or 0, qubits can be 1 and 0 at the same time, tremendously speeding up the process of discovering new blocks.


So, superposition seems like it can make Bitcoin’s computations obsolete. And yet, it’s just a part of the problem: there’s another quantum phenomena, entanglement, that makes it possible for all participants in a network to simultaneously agree on a measurement result, which pretty much sounds like consensus, a part of Bitcoin’s proof-of-work.

In layman terms, quantum entanglement is a phenomenon observed at the quantum scale where entangled particles stay connected (in some sense) so that the actions performed on one of the particles affects the other, no matter the distance between two particles.

That being said, entanglement combined with superposition seem like they’re going to kill the essential parts of Bitcoin in the near future simply because quantum computers, in theory, are able to perform all the operations super fast — but can they, really? At least, currently?

Quantum computing and Bitcoin

According to scientific research published by Tessler and Byrnes, “if it were possible to find a quantum algorithm to invert SHA-256 efficiently, then we could indeed mine Bitcoin easily. However, currently it is believed that there is no efficient algorithm, classical or quantum, which can invert SHA-256. Hence the only way is a brute force search, which classically means trying different inputs until a satisfactory solution is found.”

In the same paper, Tessler and Byrnes suggest that in three primary directions, mining, security and forks, the near term impact of quantum computing on Bitcoin appears to be rather small. The reason for this is simple. For the quantum computers to have a detrimental effect on Bitcoin, they require a larger number of qubits and breakthroughs than the quantum algorithms of today.

But let’s suggest, we’ve finally reached the moment in time where we have that quantum advantage some urban legends warn us against — well, even in this case, such advantage is not insurmountable enough that classical parallelization cannot beat it.

So, keeping all that in mind, let’s go back to the question in the very beginning of the article about quantum computing posing a threat to Bitcoin. Can it ultimately deprive digital gold of its value? It could, indeed, but what quantum computing can bring in terms of risk to the network, quantum can bring to Bitcoin's defence.

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