Researchers from NUS working on defending cryptocurrency against future attacks by quantum computers

Above photo: Dr. Miklos Santha (left) and Associate Professor Troy Lee (right), Principal Investigators at the Centre for Quantum Technologies at the National University of Singapore, and collaborators are providing advice on the quantum security of cryptocurrencies/ Credit: Centre for Quantum Technologies at the National University of Singapore

Researchers from the Centre for Quantum Technologies (CQT) at the National University of Singapore (NUS) have been retained as consultants on the security of cryptocurrency. The market for such digital currencies, which began with Bitcoin in 2009, is currently worth over US$150 billion. 

Associate Professor Troy Lee and Dr. Miklos Santha, Principal Investigators at CQT, will advise cryptocurrency provider, Hcash, on how to protect the company’s digital currency against future attacks by quantum computers. Its currency Hshare has a market capitalisation of over US$300 million as of 3 November.

Associate Professor Lee is also at the Nanyang Technological University in Singapore, and Dr Santha at the French National Center for Scientific Research or CNRS (Centre national de la recherche scientifique).

The scientists will consult for Hyperchain, which provides technical services to Hcash, along with collaborators, Associate Professor Gavin Brennen from Macquarie University, Sydney and Dr. Marco Tomamichel, Senior Lectuter from the University of Technology Sydney. They offer expertise in cryptography and quantum computing.

The researchers began discussions with Hcash, as they worked on a detailed analysis of the threat that quantum computers will pose to Bitcoin and other cryptocurrencies. That analysis, completed on 28 October, is now available as a white paper “Quantum attacks on Bitcoin, and how to protect against them”.

The paper notes that the key cryptographic protocols used to secure the internet and financial transactions of today are all susceptible to attack by the development of a sufficiently large quantum computer. Today’s small quantum computers are not a risk, but the industry is moving fast. Companies including IBM and Google are rapidly increasing the size of their machines. Algorithms already exist that, if run on big enough quantum computers, will crack many of today’s cryptography schemes.

In the white paper, the researchers estimate the speed of the quantum algorithms and project developments in quantum computing technology to place a timeline on when cryptocurrencies could become insecure.

The team analysed the ‘proof-of-work’ step used to record Bitcoin transactions, that is writing transactions to the Bitcoin digital ledger, concluding that quantum computers are unlikely to undermine this in the near term. This is mainly because specialised ASIC (Application-specific integrated circuit chips are customised for a particular use, which is Bitcoin mining here, rather than being intended for general purpose use) miners are extremely fast compared to the estimated clock speed of near-term quantum computers.

But they found that the signature scheme used by Bitcoin is much more at risk, and could be completely broken by a quantum computer as early as 2027. The signature scheme verifies ownership of digital coins. The Bitcoin signature scheme is based on ‘elliptic curve’ cryptography that a quantum computer could crack using Shor’s algorithm.  If a signature is cracked, the hacker can spend the coins, stealing them from the rightful owner.

“The main quantum bottleneck is having a quantum computer with enough qubits to run Shor's algorithm on the scheme used by Bitcoin. We estimate it would take about 500 thousand to 1 million qubits. By the most optimistic estimates, in 10 years the signature scheme of Bitcoin could be cracked in under 10 minutes by a quantum computer,” explained Associate Professsor Lee. Other cryptocurrencies that use similar security schemes will also be vulnerable.

In the white paper, the team review alternative signature schemes proposed as quantum-safe. The researchers’ work for Hcash will include recommending specific protocols to incorporate to achieve quantum security.

Associate Professor Lee said, “It’s important for anyone who protects their data or money with cryptography to be prepared for quantum computers. I am very excited to be working with Hcash, which is taking quantum security seriously and building it into the design of its coin.”


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