The hashcash proof-of-work scheme that bitcoin uses is vulnerable to Grover's quantum search algorithm, that can find a solution in the 2^76 search space for th

The hashcash proof-of-work scheme that bitcoin uses is vulnerable to Grover's quantum search algorithm, that can find a solution in the 2^76 search space for the current target difficulty in roughly sqrt(2^76) = 2^38 quantum hashing steps, for a 2^38 factor speedup. Other proof-of-work schemes (e.g. finding cycles in graphs [1]) are not vulnerable to quantum speedup. [1] https://github.com/tromp/cuckoo https://github.com/tromp/cuckoo