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 n

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'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) 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.