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Would quantum computing eventually enable you to take over the consensus mechanism on the blockchain? Do countries with cheap electricity, cold climate, and high internet bandwidth (e.g. Iceland or Norway with geothermal or hydroelectric power, low average temperature, and modern internet infrastructure) have an unfair advantage over equatorial countries? Would corporations who have control over backbone bandwidth (especially without net neutrality protection) be able to impose embargo against countries as a military weapon? These questions become more significant in a future when blockchain technology disrupts finance, contracts and all other applications of blockchain.

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Would quantum computing eventually enable you to take over the consensus mechanism on the blockchain?

Ethereum is protected from QC since it uses SHA3 as hashing algorithm.

edit: that's not true. Ethereum uses elliptic curves for public/private keys. This part need to be changed in the future to be secure.

Do countries with cheap electricity, cold climate, and high internet bandwidth (e.g. Iceland or Norway with geothermal or hydroelectric power, low average temperature, and modern internet infrastructure) have an unfair advantage over equatorial countries?

That's why China controls most of the power of blockchain networks. Currently Ethereum is moving from Proof-of-Work(calculating hashes, requires much power) to Proof-of-Stake(choose validators according to their amount of ETH). So there will be no need in accumulating computing power.

Would corporations who have control over backbone bandwidth (especially without net neutrality protection) be able to impose embargo against countries as a military weapon?

Sure, connection is an oxygen of the technology. Without connection it will split into two blockchains, not knowing anything about each other. But that's not exactly problem of blockchain(and Ethereum in particular). Will credit cards work as intended when embargo happens? Not sure.

  • Thanks. Great answers. I see your point that SHA is not affected by QC, so my question about blockchain consensus was wrong. But ECC is used in protecting ownership of a end-point address (sk/pk). So bitcoin could be stolen. I know there are asym key algos that are believed to be imune from QC... but can bitcoin and ethereum be evolved to make that sort of change? – user2942693 Dec 10 '17 at 19:08
  • That's true. I missed this part. ECC is definitely vulnerable to QC. Every blockchain can be modified to be protected in that part. All we need is to change algorithm. There're many researches on assymetric PQC. en.wikipedia.org/wiki/Post-quantum_cryptography – Andrey Putilin Dec 10 '17 at 19:27
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OK. I thought about my question a bit further. QC will (and perhaps already does) have the ability to break ECC encryption, which is used in BC and other blockchain platforms. But the problem is that it has to be used in a way that does not reveal that the QC capability exists. Just like Bletchley Park had to keep Turing's work secret. Allied ships were lost and bombing raids on UK were allowed to happen in order to keep it secret. It could not be put to use unless a plausible alternate explanation could be invented. So QC will be used in only very limited situations to avoid move to stronger post-qc-algos.

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OK. A bit more thinking on this… You only reveal a cryptographic hash (SHA256) of your public key, not your actual public key. QC works on ECC but not SHA256. So as long as you follow the practice of generating a new public/private key one for each transaction, you are safe. Thanks for that neat trick Satoshi! Great forward thinking!!! (here is a good Andreas Antonopoulos video section on this: https://youtu.be/Ibz_HMKHQl4?t=58m47s)

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