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    Author Topic: Hackers/Public will have Access to Quantum Computers in 5-10 years?  (Read 549 times)
    o_e_l_e_o
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    August 28, 2021, 12:32:44 PM
    Merited by LoyceV (2), kaggie (1)
     #41

    But wouldn't the quantum computers be able to decipher the hash of those private keys? Because they're made to make calculations that could last for about a million years to be solved shortened in a matter of seconds, will it be a threat?
    No. Not every calculation is the same. Some calculations would be exponentially faster with a quantum computer, some would be linearly faster, and some wouldn't be faster at all.

    Turning a public key in to a private key is particularly susceptible to quantum computers. A quantum computer running what is known as Shor's algorithm could reduce the number of operations required from 2128 to somewhere in the region of only 1283. This number of operations is trivial for a standard computer, and so quantum computers will eventually reach this stage also.

    However, reversing a hash and calculating a public key from an address would only experience a linear speed up. The best method for doing this, Grover's algorithm, only reduces the search space for SHA256 from 2256 to 2128. 2128 is simply too large a number to be threatened by any computer, quantum or otherwise. The entirety of bitcoin is built on security of 2128, and nothing has ever come even close to a tiny fraction to the number of operations required to break it.
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