The Threat of Quantum Computers: Will Bitcoin Get Hacked?

News and Analysis

Quantum computing has been one of the horror stories for bitcoin enthusiasts for a while now. Experts have repeatedly argued that this new tech would endanger the very existence of the network, which no one has managed to hack since its launch.

In 2019, NASA website published a document with insider information about Google’s success in the development of quantum computers and the achievement of “quantum supremacy”. The document was shortly removed from the site, but its copy is still available. The information was made public by the authoritative British media The Financial Times.

According to the paper, Google’s specialists were able to perform a computation in 200 seconds, whereas the same task would take about 10 000 years on the most powerful classic supercomputer available. The team used a processor called Sycamore initially comprising 54 qubits and later revamped to 53 qubits (quantum counterpart of bits of a classical computer). 

“This impressive acceleration compared with all the well-known classical algorithms gives an experimental implementation of quantum superiority at the computational level, and marks the onset of the long-awaited computer paradigm,” the document reads.

Accidentally or not, but this news almost coincided with a sudden short-term drop in the hash rate of the Bitcoin network by 30%, and a sharp decrease in bitcoin’s price.

Bitcoin Hashrate Chart

Social networks responded instantly, and some are still firmly convinced that the development of quantum computing means the guaranteed death of cryptocurrencies and the underlying blockchains. Gathering the opinions of experts and analysts, ForkLog has tried out to sort out the issue.

What Is a Quantum Computer?

A quantum computer is a computing device that uses the phenomena of quantum mechanics to transmit and process data. The idea of quantum computing was first proposed in the early 1980s, but a full-fledged universal quantum computer is still a hypothetical device.

The main difference between a quantum computer and most modern devices is the representation of information. Traditional computers based on transistors and silicon chips use binary code to process information. Each bit can hold either zero or one.

Quantum computing is based on the superposition principle. Instead of bits, it uses quantum bits, known as qubits. Similarly to traditional bits, qubits have two basic states—zero and one. However, due to the superposition, a qubit can take the values obtained by combining zeros and ones, and be in all these states at the same time.

The Dawn of a New Era?

The term “quantum superiority” was suggested back in 2012 by John Preskill, a Professor of theoretical physics at the California Institute of Technology. Quantum superiority is to be achieved when quantum computers can do what classical computers can’t. In a recent article for Quanta Magazine he wrote that if the news of Google’s breakthrough is true, it is an outstanding achievement both in experimental physics that signifies outstanding development of hardware for quantum computing.

However, according to Prof. Preskill, there is a catch.

“The catch, as the Google team acknowledges, is that the problem their machine solved with astounding speed was carefully chosen just for the purpose of demonstrating the quantum computer’s superiority. It is not otherwise a problem of much practical interest. In brief, the quantum computer executed a randomly chosen sequence of instructions, and then all the qubits were measured to produce an output bit string. This quantum computation has very little structure, which makes it harder for the classical computer to keep up, but also means that the answer is not very informative,” John Preskill writes.

Nevertheless, he believes that Google’s achievement is an important step in the development of applied quantum computers.

“I thought it would be useful to have a word for the era that is now dawning, so I recently made one up: NISQ. Rhymes with the word ‘risk.’ This stands for “noisy intermediate-scale quantum.” Here “intermediate-scale” refers to the size of quantum computers that are now becoming available: potentially large enough to perform certain highly specialized tasks beyond the reach of today’s supercomputers […]

The Google team has apparently demonstrated that it’s now possible to build a quantum machine that’s large enough and accurate enough to solve a problem we could not solve before, heralding the onset of the NISQ era,” the scientist added.

Is the Threat to Сryptocurrencies Real?

A significant part of people both in the crypto community and academia agree that such a threat, if any, is quite low, and the claims like “quantum computing will make blockchain technology useless” are exaggerated.

In 2018, Jeffrey Tucker, the editor of the American Institute of Economic Research online journal, wrote about this problem in his article. Quoting Dr. Gavin Brennen, a specialist in the field of quantum physics from the Australian Macquarie University, Tucker wrote that, given the level of quantum computing power available for now, negative scenarios are impossible. He notes that the existing quantum infrastructure has a relatively low quantum gate speed compared to that required to crack a cryptographic key.

According to Jeffrey Tucker, in the next 10 years, the gate speed may increase to 100 GHz. Yet, ASIC devices that are used to process PoW functions in the Bitcoin network will also evolve. According to Tucker, the development of a potentially dangerous technology will take about 10 years. He added that but by the time it’s ready, it is likely to become out of date.

Commenting Google’s reported “quantum superiority,” a well-known cryptographer and Bitcoin developer Peter Todd has also denied a possible threat to the first cryptocurrency.

“It means nothing because Google’s quantum breakthrough is for a primitive type of quantum computing that is nowhere near breaking cryptography. We still don’t even know if it’s possible to scale quantum computers; quite possible that adding qbits will have an exponential cost,” Todd wrote.

In a similar vein, an entrepreneur and crypto-evangelist Andreas Antonopoulos noted:

“Quantum supremacy, what Google described, is demonstrating the practical applicability of quantum computers to certain classes of problems.”

He added that Bitcoin developers will surely be able to update digital signature algorithms as quantum computing develops.


Although, opposing opinions exist as well. In October 2017, an international team of researchers led by Divesh Aggarwal from the Singapore Center for Quantum Technologies reported that quantum computing will become a threat to blockchain technology in the future.

They also claim that the process of Bitcoin mining is relatively safe since, in the near future, the equipment for cryptocurrency mining will still be much more powerful than quantum computers. The algorithm for creating a digital signature based on elliptical curves may eventually become more vulnerable. According to the researchers, the real threat is to be expected by 2027.

In March 2019, Jesse Lund, vice president of blockchain and digital currencies at IBM, warned about the likelihood of a threat to both the cryptocurrencies themselves and the cryptography methods involved.

“It’s reverse-engineering the private keys which represent the control of your wallet. Your public key is essentially your wallet which holds balances. And I think that’s a real, credible threat. Bitcoin is a public ledger. So you can go out and see which public keys are holding the largest balances and you could go out and target those,” he said.

Lund also noted that the threat from quantum computers will become more relevant. In the future, quantum computing will be able to calculate private keys by using public keys as a template, he stressed. Thus, according to Lund, more than half of the existing blockchain systems will be susceptible to this threat.

Associate Professor of the Russian Federation Government Financial University Vladimir Gisin believes that quantum computers really pose a certain threat to decentralized systems, blockchains, and cryptocurrencies. According to him, the Bitcoin blockchain risks being hacked when 100-qubit quantum computers appear.

“For a successful attack on a Bitcoin network, a quantum computer must have several hundred qubits. When such a computer appears, for Bitcoin in its current form, the end will come,” he noted earlier this year.

He also suggested that there may already be successful mechanisms for cracking the Bitcoin blockchain, but nothing is known about them because their authors do not want to disclose their knowledge.

“The entire security of Bitcoin is based on some hypotheses that are not fully tested. For example, on the hypothesis that the signature forgery in the Bitcoin network is computationally unreal with modern computing power. But this is a hypothesis. And although many mathematicians have dealt with this problem and none of them managed to solve it, perhaps someone somewhere has partially coped with it, we just do not know about it, because the results have not been published,” Gisin said.

At the same time, Gisin notes, it is not necessary to write off blockchains because of quantum computers, since post-quantum calculations are being developed that will be resistant to such attacks.

Cryptocurrencies Resistant to Quantum Computing

David Chaum, the “godfather” of the cypherpunk movement and the creator of the first anonymous electronic currency eCash, did not ignore the news about Google’s quantum computer. In particular, he stressed the importance of developing quantum-stable protocols.

“We have no way of knowing how far along nation-states are in developing quantum computers,” Chaum said in a statement shared with Decrypt. “In the past, government entities have broken codes and possessed cryptographic capabilities for many years without anyone knowing. The news that Google has achieved quantum supremacy strengthens my belief that quantum computing is coming and as a consequence, I believe we should all use approaches that are quantum-resistant,” Chaum said in a statement shared with Decrypt.

Chaum is also trying to draw attention to his new brainchild called Praxxis. It is a cryptocurrency based on the quantum computing-resistant blockchain, the launch of which was announced in August 2019. It is claimed that Praxxis’ consensus protocol simultaneously addresses the scalability, privacy, and security issues faced by traditional blockchains, thus providing the “pure p2p version of e-money” that Satoshi Nakamoto called for in his Bitcoin white paper.

David Chaum is not the only one working on quantum computing resistance. A project called QAN reportedly managed to achieve relatively good indicators at the beta stage.

“In cryptography, it’s best to prepare for the worst, and one can observe in recent literature that past skeptics now instantiate their crypto protocols in a post-quantum setting – just it case. Users shouldn’t worry now, but experts should prepare before it’s too late,” CTO of QAN Johann Polechak said in an interview with Forbes.

Apparently, the U.S. National Security Agency (NSA) is also developing a cryptocurrency that is resistant to quantum computing. It is difficult to say why the Agency is interested in this matter since its previous activity in crypto was limited to tracking bitcoin transactions. According to publicly available information, the NSA’s main focus is to fight online ransomware from among the geopolitical opponents of the United States, including North Korea, Iran, Russia, and China.


According to John Preskill, there is no doubt that Google and other hardware manufacturers expect to find practical applications for their work, and quantum computers will sooner or later transform our society.

At the same time, post-quantum cryptography is developing rapidly, and methods for protecting blockchains from quantum attacks have already been developed. These include the use of Lamport’s one-time digital signature, as well as the use of Merkle’s signature tree.

The hypothetical threat to cryptocurrencies, no matter how insignificant it may seem today, necessitates the creation of more secure systems. Almost everyone agrees with this, and this means that the emergence of new technological solutions is only a matter of time.

By Andrew Asmakov

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