While attention is focused at the moment on the threat that Bitmain’s crypto-mining ASIC chips pose to the security and prices of cryptocurrencies - particularly ether (ETH) and bitcoin (BTC) - an even bigger threat looms not far on the horizon: quantum computers.
Given that a quantum computer would be in the region of 17 billion times more efficient at mining the Bitcoin blockchain than a classical computer, some cryptocurrency projects already claim to have inbuilt quantum resistance in their design, such as IOTA’s Tangle network.
“A more desirable solution would be an intrinsically quantum blockchain, which is constructed out of quantum information, and whose design is fully integrated into a quantum network,” Del Rajan and Professor Matt Visser, researchers at Victoria University, New Zealand, propose in their thesis Quantum Blockchain using entanglement in time.
The novelty of their proposed network over that say of IOTA is concept of entanglement in time, or stated more radically, “it could be viewed as a quantum networked time machine.”
The authors believe the reliability of any classical blockchain modified against a quantum attack “can be questioned, given the large research effort to find new quantum algorithms, which could potentially undermine such work.”
Quantum power is the new arms race
Quantum projects have long been synonymous with superstate endeavours and has even been dubbed the “new arms race”. The Chinese government is spending $10 billion building a National Laboratory for Quantum Information Sciences in Hefei, due to open in 2020, and this is just part of their overall budget for quantum projects. China is also notorious for its cyberwarfare efforts and, according Foreign Policy magazine, the number of computer hackers on the government payroll is somewhere between 50,000-100,000.
The European Commission recently committed €1b on quantum research and although the US government has cut back its spending, it’s spending roughly $200m a year on research, according to a 2016 report.
Where it might take a contemporary supercomputer decades to solve a problem, it will take a quantum computer just several days, and, like the space and nuclear races, the first country to get there will set the rules for years to come - taking state surveillance and interference to another level.
Scalable quantum computers would successfully break the cryptographic protocols that are used to secure (classical) blockchains, as well as the digital security of the modern world.
Let’s get metaphysical: What is quantum information?
Classical information and classical computer programming is written down in terms of bits in binary form of 0s and 1s. Quantum cryptography works with quantum bits, qubits, which cannot be copied and are in superposition of 0 and 1, meaning they can be both at the same time and run many calculations simultaneously.
The superposition effect is best imagined as a particle that can move in multiple directions at the same time.
A fundamental difference in quantum cryptography is that qubits, unlike classical bits, cannot be copied, as any storage of data in a classical sense destroys the superposition phenomenon which gives the quantum computer its exceptional computing power - power that would undermine the hashing cryptography in classical blockchains by falsifying historical data in previous blocks without changing the outcome of the hashing function.
Benefits of quantum entanglement
Rajan and Visser suggest that “entanglement in time, as opposed to entanglement in space, plays the pivotal role for the quantum benefit over a classical blockchain.”
The “quantum benefit” they refer to is the ability to be rendered “tamper proof”.
Spatial entanglement: If an attacker tries to tamper with any photon, the full blockchain would be invalidated immediately; this already provides a benefit over the classical case where only the future blocks of the tampered block are invalidated
Temporal entanglement: This involves an entanglement between photons that do not share simultaneous coexistence, yet they share non-classical measurement correlations. Stated more shockingly, “in our quantum blockchain, we can interpret our encoding procedure as linking the current records in a block, not to a record of the past, but linking it to the actual record in the past, which does not exist anymore.”
The most important aspect of “tamper proof” security in quantum cryptography is quantum key distribution (QKD), where a sender uses a cryptographic key encoded in a quantum signal to encrypt a message and if there is any attempt to intercept the key it will be destroyed.
IBM's 50-qubit quantum computer
Commercializing quantum computers
Technology giants like IBM, Google and Microsoft are also racing against their rivals for “quantum supremacy”, which will someday be powering business. Last November, IBM revealed the world’s first 50-qubit quantum computer, and although it has been able to simulate molecules and other chemical experiments IBM Research Vice President Jeffrey Welser said when it will be put to use “for something the public will understand in terms of an application they would use themselves, I can’t really speculate.”
In March, Google unveiled its 72-qubit Bristlecone quantum chip with gusto; the project’s leader John Martinis even updated its forecast to reach quantum supremacy by the end of the year. But in mimicry of state rivalry, China’s largest retailer Alibaba, which is also vying for supremacy, cut Google down with its own research on the chip that suggested that it hadn’t reached that point at all as the error rates were too high.
While they are still a way off commercial or practical use, the first company to make the breakthrough will be able to rent or sell their machines to other companies eager to enter the market - like Daimler and JP Morgan who have been exploring how they could improve battery life and financial models.
Quantum internet: One louder than Internet of Things?
At the moment a key link is missing in the infrastructure needed to make a quantum blockchain, that is a global quantum network connecting devices by fibre links and satellites, eventually leading to quantum internet. Though Rajan and Visser concede this is still in the works they affirm that all the “subcomponents of the system have been experimentally realized”.
Quantum cryptography is the most developed of all the branches of quantum physics, and given the progress of blockchain development, we could see more projects come to life that look even further past the age of the Internet of Things.
Perhaps quantum information science will be the final frontier for blockchain?