In this article we review what the recent breakthroughs in the development of quantum computers mean for bitcoin, and what risks they may pose to bitcoin’s cryptographic security.

What Does Quantum Computing Mean for Bitcoin’s Security?

A couple weeks ago, Google announced that it had achieved “quantum supremacy,” publishing an article on a NASA website that suggested it had built the world’s fastest-ever quantum supercomputer. Although the article was later retracted by Google for what was likely to be the reason of not meeting specific standards when it came to peer review, it was up for long enough to be downloaded and read by hundreds of experts in the field. Opinions are highly mixed on what the results actually mean, with some experts proclaiming a new dawn of computing had emerged and other saying that Google hadn’t even built a quantum computer at all.

The term “quantum supremacy” refers to the idea of a quantum computer being able to solve a specific problem that a classical computer could not. According to Google’s team of researchers, its computer was able to perform calculations that would take a regular computer more than 10,000 years in about 200 seconds. This is a stunning feat in itself, but critics are pointing to the fact that the computational task was specifically geared toward quantum computers, and the computer itself could still not perform several basic computational tasks that regular computers can. Among the least impressed at Google’s feat are bitcoin developers, who for the most part see no threat by these recent developments.

Quantum Computing and Bitcoin

What does the imminent expansion of quantum computing technology mean for bitcoin and most other cryptocurrencies, whose blockchains and security rely on encryption that could potentially be broken quantum computers? At the moment, not much, but it suggests that in all likelihood the time will come when blockchains such as that of bitcoin’s will need to be upgraded to become quantum resistant. Given the fact the technology is still several years away from commercial viability, or even being at the level necessary to crack bitcoin’s cryptography, it means bitcoin still has time to prepare itself for the eventuality of quantum computing.

Currently, calculation of a bitcoin private key as derived from a public key currently requires 2^256 guesses — a number so large that all the computers in the world connected to one another could not compute it. However, by employing a quantum computing algorithm known as Shor’s algorithm, this number can be drastically reduced, thereby making the process of deriving a private key from a public one significantly easier. Theoretically, once a private key is “reverse engineered” or even “brute forced” from a public one, the contents of a bitcoin wallet can be emptied, which would have a devastating effect in the public’s confidence in bitcoin, leading to crash in price.

According to bitcoin developer and Blockstream co-founder Peter Wuille, bitcoin will still retain some degree of cryptographic security even after quantum computing, thanks to the fact most bitcoin public keys are not known, and cannot be known until coins are spent from a related address.

“Assuming QC “suddenly” appears, and ECDSA is instantaneously crackable using Shor’s algorithm, and SHA256/RIPEMD160 becomes vulnerable to Grover’s algorithm:

Every unspent coin, sent to an address whose pubkey is not yet revealed, is somewhat safe (80 bit security left, instead of 160 bit)

The block chain is quite safe (128 bit security left, instead of 256 bit)

Transactions to new quantum-computing-based addresses with corresponding keys, are safe

… only unspent coins sent to reused addresses will be trivially claimable by any attacker (a few bits of security left, instead of 128 bit)” – Peter Wuille

So, are quantum computers actually a threat to blockchain security? According to quantum computing expert Johann Polacsek, the answer is both ‘yes’ and ‘no’.

“We should definitely be worried… Many IT professionals and CTOs… are neglecting and denying quantum computing threats with the simple reasoning that once it’s seriously coming, we’ll have to redesign almost everything from scratch, and that must surely be a long time ahead…

The truth is that one can already rent quantum computers for experimenting with possible attack algorithms and testing theoretical approaches. The maths behind breaking currently used public key cryptography – EC and RSA – were proven, we just need more qubits…

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 in case. Users shouldn’t worry now, but experts should prepare before it’s too late.” – Johann Polacsek

How does quantum computing work?

The field of quantum computing began with the work of Paul Benioff and Yuri Manin in 1980, Richard Feynman in 1982, and David Deutsch in 1985. The answer to the question of how quantum computers work long, complicated, and not entirely understood. Microsoft offers the following definition, which is as good of a summary of such a complex topic as any:

“In quantum computing, a quantum bit is a unit of quantum information—like a classical bit. Where classical bits hold a single binary value such as a 0 or 1, a qubit can hold both values at the same time. When multiple qubits act coherently, they can process multiple options simultaneously. This allows them to process information in a fraction of the time it would take even the fastest nonquantum systems.”

For the moment, running a quantum computer requires the production of extremely cold temperatures, which is one of the reasons why it is a prohibitively expensive undertaking. In order for a quantum computer to function sub-atomic particles must be as near as possible to a stationary state in order to be measured. For example, the cores of D-Wave quantum computers – one of the industry’s leading manufacturers of quantum computers – operate at -460 degrees ℉, or -273 degrees °C, which is a mere 0.02 degrees above absolute zero.

One possible explanation for why quantum computers work involves the concept of the multiverse, or parallel universes. The concept revolves around the idea that there are several (or an infinite number of) hidden universes that exist in tandem with our own and their existence can only be detected through quantum phenomena. It has been theorized that qubits are able to exist in two states simultaneously because they are being observed in multiple universes simultaneously. According to one of the leading experts in the field, physicist David Deustsch:

“Quantum computation is… nothing less than a distinctly new way of harnessing nature… It will be the first technology that allows useful tasks to be performed in collaboration between parallel universes, and then sharing the results.” – David Deutsch, Physicist at the Centre for Quantum Computation, Oxford University

A component of a quantum computer known as a dilution refrigerator. Source: Getty Images

Other Contenders in the QC Arena

Google is hardly the first to make strides in the development of quantum computers. Some other notable quantum computing initiatives include:

D-Wave Systems – this enterprise-specific company launched what was thought to be the world’s fastest and most sophisticated commercially-available quantum computer in May 2011, named D-Wave One. The company has a mission statement of “unlocking the power of quantum computing by delivering customer value through practical applications.” D-Wave has worked with NASA, MIT, Harvard, Google and Lockheed Martin, and service a number of clients through their cloud-based quantum computing application solution.

Intel Tangled Lake – announced by processor manufacturing giants Intel in January 2018, Tangled Lake is an initiative to ready quantum computer for commercial production within 10 years.

Ali Baba – the Chinese search engine-based conglomerate launched a “Superconducting Quantum Computing Cloud” in March 2018, in conjunction with the Chinese Academy of Sciences (CAS).

Microsoft Quantum Network – first announced by Microsoft in February 2019, which formalized a previous coalition of partnerships into the quantum computing space. In May, Microsoft made its Quantum Development Kit software open source and available to the public.

IBM Q – since 2016, IBM has been providing access to cloud-based quantum hardware, unveiling the IBM Q System One commercial quantum computer in January 2019. IBM describes their product as the first fully-integrated quantum computing system designed for commercial use.

More Realistic Use-Case Scenarios for QC

Of course, application of the power of quantum computers isn’t limited to trying to break encryption algorithms or mine bitcoin. Notable applications for which quantum computing will primarily revolve around simulation of events in the physical world, including:

  • Quantum molecular modeling. Also known as ‘quantum chemistry,’ this field involves using quantum computing to build accurate simulations of molecular systems — a task which just isn’t feasible using classical computer systems. This can significantly speed up and improve the design of pharmaceuticals, leading to breakthroughs in drug discovery and potentially help save millions of lives in the long run.
  • Quantum simulations of the weather, climate and the environment. It has always been the case that the best weather prediction models could not accurately forecast the weather for longer than 6 hours into the future due to the emergence of too many chaotic variables. Quantum computing can also change to allow for millions of simulations to be run nearly instantaneously, allowing for longer-term forecasts with greater degrees of accuracy, which can also be applied to climate and environmental modeling.
  • Cognitive computing. Today, we are entering a new age in computing that is defined by using computing power for predictive purposes. This can be seen in the rise of artificial intelligence-based platforms, and as applied to cryptocurrency, DAO-type platforms like Maker (MKR) and Augur (AUG). Quantum computing can undoubtedly speed up the development of AI technology by allowing programs guided by neural networks to learn at a much faster rate than previously allowed. Ultimately, quantum computing is likely to play a role in the synthesis of human beings and machines; whether it will result in cyborg-like creations or indefinite increases in lifespan remains to be seen.

In June, Google revealed that the power of their quantum processors was increasing at a doubly-exponential rate. This rate of development, dubbed “Nevan’s Law,” was what allowed Google to make its proclamation that it would achieve “quantum supremacy” before the year’s end. It is likely that Google will make even greater strides in development in the near future, but it is highly unlikely that the first thing they will do, after it becomes possible, will be undermine the cryptography of the bitcoin network.