Quantum-proofing digital money

As developments in computer science promise huge advances in processing power, some cryptocurrency designers are aiming to ensure their digital moneys’ underlying code does not become obsolete.

Cryptocurrencies—and all the world’s internet-based commerce—rely on a discovery made by mathematicians in the 1970s.

Public key cryptography, introduced by Diffie, Hellman and Merkle in 1976, was a revolutionary invention. It allowed for secure electronic communication across a large network of participants and between people who don’t know each other.

Earlier versions of cryptography had far more limited applications, since they relied on the people wishing to communicate in secret exchanging their encryption ‘key’ in advance.

Public key cryptography uses mathematical functions that are easy to perform in one direction, but which are hard to reverse, making code-breaking infeasible even for the largest computers.

For example, the ‘RSA’ algorithm, introduced by Rivest, Shamir and Adleman in 1978, is founded on the mathematical difficulty of finding two prime number factors of a very large number. Prime number factors are the ‘building blocks’ of all whole numbers.

Another form of public key cryptography, introduced in the 1980s, uses the mathematical properties of elliptic curves. So-called elliptic curve cryptography underpins the security of bitcoin and many other cryptocurrencies.

However, recent advances in computer science put public key cryptography at risk—at least on paper.

Quantum computers have exponentially more processing power

Classical computing relies on the communication of information in a stream of binary digits or ‘bits’.  As their name suggests, bits can exist in one of two states—zero or one.

By contrast, quantum computing relies on the strange properties of sub-atomic particles, as expressed by the laws of quantum mechanics, a branch of physics discovered in the early 20^th century.

In quantum computing, rather than representing bits (a binary choice between zero and one), particles can represent quantum bits, or ‘qubits’. A qubit could take on the value zero, one, both, or neither, simultaneously.

As a result of this strange property of sub-atomic physics, quantum computers have exponentially more processing power than traditional computers.

And, in theory, they could therefore crack the hitherto irreversible algorithms of public key cryptography, placing the security of cryptocurrencies—and the whole of internet commerce—in jeopardy.

However, the existing versions of public key cryptography are not obsolete yet.

Since they rely on the behaviour of sub-atomic particles, quantum computers are notoriously difficult to build and operate, since the slightest interference or imprecision can affect the results of the computation being performed.

Up to now, scientists and engineers have only managed to produce practical implementations of quantum computing that fall well short of the processing power needed to crack existing encryption algorithms.

“This technology will remain five years in the future for some time”

IBM, for example, currently offers a 20-qubit quantum computer for scientific and commercial use. However, estimates of the number of qubits required to break the RSA or elliptic curve algorithms that are used in public key cryptography range from 2000-4000 qubits.

“In my opinion it’s still at least five years in the future, and it will remain five years in the future for some time,” Jérome Rousselot, a computer scientist and founder of Jita, an advisory business specialising in blockchains, told New Money Review.

Nevertheless, some cryptocurrency designers, mindful of the potential threat represented by quantum computing, are already moving to ‘quantum-proof’ the encryption algorithms backing their digital moneys.

For example, ABC, a digital currency launched in 2018, uses an encryption algorithm based on so-called multivariate cryptography, specifically a form called a rainbow signature.

This algorithm relies on the difficulty of solving systems of polynomial equations and is theoretically resistant to quantum computing. ABC’s software is open source and is available in the code repository GitHub.

Speaking at a recent Coinscrum event in London, Jin Liu, chairman of the ABCMint foundation, says his organisation also plans to develop quantum-resistant cryptocurrency mining hardware and a quantum-proof online exchange for cryptocurrencies.

Post-quantum computer science is still in its infancy, however.

“Have a look, you can check it”

“Around the world fewer than 50 people can code a post-quantum computing algorithm,” Jin Liu told New Money Review.

And while the science is in its infancy, it awaits broader adoption even among tech-savvy cryptocurrency experts.

“Up to now it’s been difficult to persuade the bitcoin community of the need to be quantum-proof,” Jin Liu said.

“That’s why we launched a new cryptocurrency. We want to take it as a mathematical experiment and tell all the other guys, ‘Have a look, you can check it’.”

Jita’s Jérome Rousselot believes that eventually most existing public key cryptography algorithms will be redesigned to resist advances in computer processing power.

“The day quantum computing becomes a problem for existing cryptographic algorithms, we can replace them broadly across e-commerce, in military systems and in bitcoin and other cryptocurrencies as well.”

However, cautions Rousselot, in an area of such complex science and engineering, moving slowly and surely is important.

“It’s good to test a new concept like a quantum-proof algorithm on a new cryptocurrency before incorporating it into a larger network like bitcoin,” said Rousselot.

“It needs to be proven to be secure.”

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