Hashcash, the proof of work system employed by Bitcoin with hash function SHA256, is also vulnerable.
Where a current mining chip might search a space of 6e13 nonces in 10mins, a quantum computer employing Grover&#x27;s algorithm might be able to search a space of 1e18 nonces,
even with much fewer circuits and slower cycle time
(although in Bitcoin this is complicated by having limited nonce entropy in the header)<p>Note that the potential for speedup is due to the extremely small time needed for a single proof attempt. A PoW that only allowed a hundred proof attempts in the block interval time would hardly be vulnerable.