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.
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
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.
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.
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.
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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