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A new quantum cryptography-based Bitcoin standard has been proposed that could harden the popular cryptocurrency against the advent of full-fledged quantum computers. Bitcoin as it now exists involves traditional public key cryptography and thus could conceivably be hacked by a future quantum computer strong enough to break it. However, quantum cryptography, which is based not on difficult math problems but the fundamental laws of physics, is expected to be strong enough to withstand even quantum computer-powered attacks.

The proposal, dubbed qBitcoin, posits transmission of quantum cryptographic keys between a remitter and a receiver of the eponomous named cryptocurrency, qBitcoin. The system would use provably secure protocols such as theBB84quantum key distribution scheme.

To exchange qBitcoin, then, requires that there be a transmission network in place that can send and receive bits of quantum information, qubits. And that is no mean feat, considering it typically involves preserving the polarization states of individual photons across thousands of kilometers. To date, there are five knownquantum key distributionnetworks in the United States, Switzerland, Austria, and Japan. China is working ontheir ownmassive 2000-km link, as well. And a number of satellite-to-satellite and satellite-to-ground quantum key distribution networks are alsobeingdevelopedandprototyped.

Which is to say that qBitcoin or something like it could not be scaled up today. But if the quantum computer singularity is approaching, in which a powerful enough machinecould threaten existing cryptography standards, quantum cryptography would be an essential ingredient of the post-Y2Q age. So existing quantum key distribution networks might at least serve as outposts in a burgeoning global quantum network, like Western Union stations in the early days of the telegraph.

Some things about qBitcoin might appear the same to any Bitcoin user today. Bitcoin is a peer to peer system, and qBitcoin is also peer to peer, says Kazuki Ikeda, qBitcoins creator and PhD student in physics at Osaka University in Japan.Hesays compared to Bitcoin, qBitcoin would offer comparable or perhaps enhanced levels of privacy, anonymity, and security. (That said, his paper that makes this claim is still under peer review.)

However, the lucrative profession ofBitcoin mining, under Ikedas protocol, would be very different than what it is today. Transactions would still need to be verified and secured. Butinstead of todays system of acryptographic puzzles, qBitcoins security would rely on a 2001proposalfor creating aquantum digital signature.Such a signature would rely on the laws of quantum physics to secure the qBitcoin ledger from tampering or hacking.

Ikeda's proposal is certainly not the first to suggest a quantum-cryptographic improvement onclassical-cryptography-based digital currencies. Other proposals in2010,2016,and evenearlier this yearhave also offered up variations on the theme. All work to mitigate against the danger large-scale quantum computers would represent to Bitcoin.

Of course, not every solution to the quantum singularity is as promising as every other. A person going by the handle amluto criticized Ikedas qBitcoin proposal onaprominent message boardlast week. (amluto claimed to be author of one of aprevious quantum currency proposalsfrom 2010presumably the 2010 proposals co-author Andrew Lutomirski, althoughIEEE Spectrumwas unable to confirm this supposition at press time.)

This is nonsense It's like saying that you can transmit a file by mailing a USB stick, which absolutely guarantees that you, the sender, no longer have the original file. That's wrongall that mailing a USB stick guarantees is that you don't have the USB stick any more, not that you didn't keep a copy of the contents. Similarly, quantum teleportation eats the input state but says nothing about any other copies of the input state that may exist.

Ikeda says he disagrees with the analogy. The point, he says, is that there are no other copies of the input state as it's called abovein other words of the quantum keys that secure qBitcoin. So, Ikeda says, qBitcoin is safe just like Bitcoin is safe today.

But one day, thanks to quantum computers, Bitcoin, will no longer be safe. Someone will needto save it. And, no matter who devises the winning protocol, the thing that threatens Bitcoinmay in fact also be the thing that comes to its rescue: The cagey qubit.

Read more:
qBitcoin: A Way of Making Bitcoin Quantum-Computer Proof? - IEEE Spectrum