# Will Quantum Computing Impact the Blockchain Space?

2022年 2月 23日*Originally published May 26, 2021; Updated February 21, 20221*

Much has been made of the likely advent of quantum computing, which promises the ability to perform computations at speeds that are orders of magnitude beyond those of current computers. But what does quantum computing mean for the future of blockchain? Do quantum computers threaten blockchain security?

To answer this question, it's important to first explore the history of quantum computing as a concept—its origins, its objectives, and the strides it has made in recent years. From this starting point, it is possible to analyze the ways in which the technology stands to impact blockchain projects—and what that means for the decentralized space generally.

### What is Quantum Computing?

The main difference between quantum computers and standard, or "classical," computers is the way that they process information. Classical computers use pieces of data called "bits" to store information in one of two states: 0s and 1s. Each of these 0s and 1s represents high- or low-voltage electrical signals that the computer interprets into what we see on our screens. **Quantum computers**, on the other hand, store information in **quantum bits**, or "**qubits**"—floating point states that act like a probability cloud rather than a binary yes/no statement. Qubits' high level of complexity gives quantum computers the potential to process data exponentially faster than classical computers; in theory, they could solve computation problems that have been deemed impossible for classical computers.

### Quantum Computing: a Brief History

The research describing the principles of quantum computing appeared in the late 1970s and early 1980s. In 1979, Paul Benioff, a physicist at Argonne National Labs, published a paper that demonstrated the theoretical basis for quantum computing, and went on to suggest that a quantum computer could be built. Then, in 1980, mathematician Yuri Manin explored the concept further in his book, *Computable and Non-Computable*.

But the concept of quantum computing started to gain real traction for the first time in 1981, when a theoretical physicist named Richard Feynman delivered a lecture entitled "Simulating Physics with Computers" at the Massachusetts Institute of Technology (MIT). During this talk, Feynman outlined a problem: classical computers were incapable of recreating natural phenomena in an efficient way.

"Nature isn't classical," he said. "If you want to make a simulation of nature, you'd better make it quantum mechanical." Feynman argued that by creating a computer that operated on the principles of quantum mechanics, computing could become exponentially faster and more efficient.

Then in 1985, David Deutsch published his seminal paper "Quantum theory, the Church-Turing principle and the universal quantum computer," in which he envisioned the creation of a quantum Turing machine. Deutsch, whose work in the field has led him to be widely regarded as the godfather of quantum computing, said that "Quantum computation ... will be the first technology that allows useful tasks to be performed in collaboration between parallel universes."

Thirteen years later, in 1994, mathematician Peter Shor developed his famous algorithm. Shor's algorithm was so powerful at factoring integers that its very existence implied that public key cryptography could be easily broken with a powerful enough device.

Essentially, the algorithm proved that quantum computers could solve complex problems much faster than even the most advanced traditional supercomputers. For example, factoring 300-digit numbers would take a traditional computer thousands of years—but with Shor's algorithm, a quantum computer could theoretically perform this task in a matter of hours.

Like Feynman's 1981 lecture, the development of Shor's algorithm sparked a wave of interest in quantum computing. Two years later, in 1996, computer scientist Lov Grover created a database search algorithm for quantum computers. The algorithm is capable, in theory, of solving problems that involve random or brute-force search computations four times faster than a classical computer.

In 1998 the first-ever working quantum computer was built. The device operated with just two qubits. Nearly ten years later, Canadian startup D-Wave built a 28-qubit quantum computer. From there, the growth of quantum computing has been explosive. In 2017, a computer built by IBM and several university teams had 50 qubits; in 2018, Google unveiled Bristlecone, a quantum computing chip that contained 72 qubits.

With the launch of Bristlecone, Google claimed that it had achieved "quantum supremacy"--that the chip could demonstrably solve problems that no classical computing device could solve in any reasonable amount of time. (This claim was later disputed.)

### Meaningful Quantum Computing May Still be Five to Ten Years Away

But while much progress has been made in the world of quantum computing, experts believe that it could be five to ten years before the technology is at a point where it can deliver meaningful value. Still, that day is coming closer and closer. While the quantum computing industry was valued at roughly $507.1 million in 2019, it is projected to grow to as much as $65 billion by 2030.

### The Quantum Internet and the Future of Data Security

Quantum computing has the potential to revolutionize the entire Internet, giving rise to the so-called "Quantum Internet," which will allow devices to exchange information using the principles of quantum mechanics. The Quantum Internet could also act as a platform for online communication and computational processes that are not possible with classical computing methods.

The Quantum Internet promises much higher levels of digital security than were previously possible. A prime example of this potential is **quantum key distribution (QKD)**, which could vastly improve encrypted communication. Just like traditional encrypted messaging and data transfer, QKD algorithms would share cryptographic keys between two or more entities that would allow them to privately exchange information. However, QKD can also make the exchange of encryption keys completely secret; it could even warn users of the presence of an onlooker.

Additionally, quantum computers could allow for **truly random number generation**. The generation of random numbers is essential for secure encryption—but traditional computers actually rely on "pseudo random" number generators in most cases. Because the numbers generated by these programs are not *truly* random, they are still at risk of being compromised.

Quantum computing will also impact, and potentially improve, the financial services, tools, and infrastructures that society relies on. And because quantum computers are particularly well-suited to sorting through reams of random data, they promise to vastly improve automated risk assessment and prediction models.

Quantum computers theoretically have unparalleled abilities to identify patterns, categorize, and make predictions that are not possible today. For example, a bank could use quantum computing to improve algorithms and models that calculate statistical probabilities, and thereby predict the likelihood of unusual activity that could affect financial markets. The data-sorting capabilities of quantum computers could also have major implications for optimizing trading data, which could enhance investment gains and possibly open the door for new investment opportunities.

### What Will the Advent of Quantum Computing Mean for Blockchains?

But for all the possible benefits that quantum computing can bring to the world, there are some elements of the technology that have caused concern among some people. In particular, it has been suggested that quantum computing threatens the viability of blockchain technology because of the latter's use of **asymmetric cryptography**, also known as **public-key cryptography**.

With asymmetric cryptography, private and public keys are generated in pairs. The private key is kept secret, while the public key is made publicly available. Asymmetric cryptography is based on a mathematical principle called a "one-way function," according to which a public key can be easily derived from a private key, but not the other way around.

On a blockchain, public keys are used as wallet addresses; private keys are used to access the funds in a cryptocurrency wallet. With classical computing methods, a public wallet address can be derived from a private wallet key, but private keys can't be derived from public addresses.

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When quantum computers enter the mix, however, it's a different story.

Using Shor's algorithm, a quantum computer could theoretically determine the private keys associated with any public wallet address on a blockchain. This would obviously pose an existential threat to blockchains as they currently exist. But such a scenario is not likely to become reality.

In order to understand why blockchain cryptography is likely to thrive—even in a world of quantum computing—it's useful to take a closer look at why cryptographic algorithms could be vulnerable to quantum computers in the first place.

Classical computers use "bits" of data; similarly, the security of any cryptographic algorithm is measured in "bits of security." This measuring tool provides a method of comparing the strength of different encryption algorithms: for example, it would take 2,128 classical computational steps for an attacker to crack an encryption algorithm that provides 128 bits of security.

However, when it comes to quantum computing, the number of steps required to crack cryptographic algorithms is drastically reduced. For example, Shor's algorithm can be used to reduce the security of a 3,072-bit RSA key to just 26 bits of security—a level that could be cracked with the computing power of a cell phone.

If large and powerful quantum computers begin to exist on a widespread scale, the power of many public-key cryptographic algorithms could be rendered virtually obsolete.

### The Advent of Quantum Blockchain

But while some kinds of encryption are vulnerable to quantum, so-called "quantum-proof" algorithms are already being developed by high-profile research organizations. And even some of the more common kinds of encryption can be "quantum-proof" if they are used correctly. For example, Advanced Encryption Standard (AES) encryption with security of more than 256 bits is said to be quantum-resistant.

The rise of quantum computing will mean encrypted messaging applications, VPNs, and cryptocurrency networks that rely on non-quantum-proof cryptographic algorithms will eventually need to make the shift to quantum-proof algorithms. But this change is evolutionary, not existential: the continued growth and development of technology in general is fundamentally premised on individual concepts advancing and changing to keep pace with each other.

And the reality is that quantum computers and blockchain technology can co-exist, work together, and strengthen one another.

### The Dawn of Quantum and Quantum-Proof Blockchains

The combination of quantum computing and blockchain technology has come to be known as "**quantum blockchain**". Like classical blockchains, quantum blockchains are decentralized, encrypted ledgers. However, unlike classical blockchains, these networks would be based on quantum computation, quantum information theory, and quantum mechanics.

While no quantum blockchain is yet operational, a number of researchers are exploring the potential of the technology.

In 2018, researchers at Victoria University of Wellington, in New Zealand, proposed a quantum blockchain model that would store blockchain data in a quantum era: pieces of transaction data would be preserved in entangled photons that only exist for a short time. Afterward, though, the photons would still be readable--encased forever in a sort of "read only" mode, impossible to alter.

A number of other efforts to build quantum-proof blockchains have emerged since then. Ethereum Foundation researcher Justin Drake explored the concept of a quantum resistant "Ethereum 3.0" at the StarkWare conference in 2019. Additionally, projects like the Quantum Resistant Ledger and Bitcoin Post-Quantum have been developing algorithms that will guard against quantum technologies in the future. Cambridge Quantum Computing is currently working on quantum security technology that "can be applied to any blockchain network." It aims to secure both the communications among computers storing blockchain data and the signatures used to encrypt and sign blockchain data.

"The entanglement in time, as opposed to an entanglement in space, provides the crucial quantum advantage," the report reads. "All the subcomponents of this system have already been shown to be experimentally realized. Perhaps more shockingly, our encoding procedure can be interpreted as non-classically influencing the past; hence this decentralized quantum blockchain can be viewed as a quantum networked time machine."

In theory, this technology could be used to create an immensely secure blockchain.

In 2019, an independent team of researchers also proposed the creation of a new type of cryptocurrency dubbed the "quantum coin," arguing that quantum blockchains could produce more secure and efficient transactional models. The researchers proposed the combination of quantum entanglement and Distributed Proof-of-Stake (DPoS) to create a new kind of consensus mechanism that would be faster and more efficient than pre-quantum blockchain consensus algorithms.

But while quantum technological developments are happening faster than ever, it will still be years before quantum computers are a reality. In the meantime, cryptocurrency users and developers can take the necessary steps to quantum-proof the blockchain networks that they rely on. And when quantum supremacy arrives, the blockchain projects should be prepared to innovate and thrive.

### Quantum Computing is a Seminal Opportunity for Blockchain

Quantum computing is not a threat to blockchain technology. On the contrary, it has the potential to exponentially accelerate the positive impact of decentralized projects, and greatly strengthen online privacy, by enabling standards of encryption and immutability that are not possible today. The rise of quantum blockchains would represent the fulfillment of a great deal of technological promise and would greatly benefit people around the world.

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