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Comment by Erlich_Bachman | Hacker News Reader

They would just switch to another algorithm. Sad for all the miners who bought ASICs, doesn't change a thing for all users and investors. It would just be a hard-fork. It would not be the first one, and it would very likely be quite a consensual one, since no user wants their transactions to be unsecured.

I really wish people would research a bit more before posting these questions here. The quantum computing argument has been asked a thousands times before, it was first seen shortly after the bitcoin paper was published, it has been answered and re-answered and re-answered so many times, everywhere. And yet here we are filling the internet with more and more copies...

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The issue is the private keys become vulnerable not just the hashing algorithm. If 3/4th of Bitcoins are in lost wallets in 1,000 years those instantly flood the market once someone can discover them from the old public keys. You can’t distinguish between someone that’s kept a wallet inactive for all this time and someone discovering a private key.

Which means you need to fork early and abandon any wallets that don’t do a transaction with the new system. That’s not the kind of transition that works with just the miners involved.

You can trivially distinguish those transactions from real ones. In fact so trivial that you could do it in one if clause

    #define LATEST_BLOCK_BEFORE_EMERGENCE_OF_QC 76283747
      # fill in number when that happens

    if (block_height>LATEST_BLOCK_BEFORE_EMERGENCE_OF_QC) {
       # Treat transaction as invalid if it still uses SHA256 
    }

You know transactions are timestamped through the medium of being included in a block, right?

You don’t understand, this has nothing to do with SHA256 for mining after crypto. You need to sign a transaction with a private key. Quantum crypto makes all current private keys public.

This means you need to pick some date where everyone with a private key needs to create a new key under a new system. Then before quantum crypto is available they need to make this transaction from their old wallet using an old key to a new wallet with a new secure private key. And they need to do this before quantum crypto is available.

Yes? That's exactly what they'll do.

How and when? People are working on quantum crypto right now and as far as anyone know someone could literally break Bitcoin tomorrow February 24th 2020. It seems unlikely, but the same could be said for every day until it happens.

hopefully tomorrow is in 2021, regardless of time zone or day and month.

Common misconception, real programmers use zero indexed years. None of this 1BC/BCE to 1AD propaganda people keep sprouting. ;-)

Current record for quantum factorisation using Shor is 21, done by IBM in 2019.

Current public record, NSA etc don’t publish their research.

Shor's algorithm can be used for solving the discrete logarithm problem significantly faster (digital signing), but the miners are safe, so only a soft fork is needed.

Work is on the way to standardize a quantum-safe digital signature, but it takes years to get the best solution, and right now there's no time pressure.

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