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Quantum-secured blockchain (arxiv.org)
59 points by blopeur on June 3, 2017 | hide | past | web | favorite | 9 comments

> current blockchain platforms rely on digital signatures, which are vulnerable to attacks by means of quantum computers

There are many digital signature schemes (such as SIDH, New Hope, Lamport+Merkle, SPHINCS, etc) which are not vulnerable to any important quantum attacks.

Yea, it's baffling that the abstract doesn't mention post-quantum crypto and make some sort of argument that it's somehow not vastly easier to implement.

SIDH and New Hope are not signature schemes.

How do they work? Are they just difficult to write quantum algorithms for or is there some fundamental mathematics involved that stops a quantum computer enumerating the solutions?

To the best of my knowledge there's not even any known mathematical theorem that would prevent such algorithms on regular computers. I don't see how this would be any different for quantum computers.

That is correct. Any proof that digital signatures are secure on classical computers would imply P != NP.

Further, it is known that BQP (bounded error quantum polynomial time. The quantum computer equivalent of P) is contained in PSPACE. However P=PSPACE is still an open question. This means that we still do not have any theoretical proof that quantum computers are more powerful that classical computers.

The blockchain itself is for most cryptocurrencies already quantum-proof, since they rely on hashing blocks until some number of leading zeroes is met. That is the blockchain part.

What the paper seems to target is quantum-proof account management, a problem which atleast on the Ethereum blockchain is trivial to solve at the moment with some inconvenience and with later Hardforks implementing the account abstraction, will be part of how the chain works. Everyone can then just use a Lamport/Merkle signature, SIDH, New Hope, whatever, as long as it can be implemented on the EVM.

I'm not certain why we need to throw quantum-computing at the blockchain until some arbitrary amount sticks that can be declared "secure".

I agree that we need to implement postquantum computing algo's for both hashing (proof of work function) and signing (transaction authentication). I don't agree we should build a QKD network of p2p fiber to er this. SIDH is looking the most attractive for the postquantum signing, at least.

I call shenanigans! No way a six-page paper demonstrates "an experimental realization of a quantum-safe blockchain platform that utilizes quantum key distribution".

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