  We make several contributions that quantify the real-time hash rate and
therefore the consensus of a blockchain. We show that by using only the hash
value of blocks, we can estimate and measure the hash rate of all miners or
individual miners, with quanti able accuracy. We apply our techniques to the
Ethereum and Bitcoin blockchains; our solution applies to any
proof-of-work-based blockchain that relies on a numeric target for the
validation of blocks. We also show that if miners regularly broadcast status
reports of their partial proof-of- work, the hash rate estimates are signi
cantly more accurate at a cost of slightly higher bandwidth. Whether using only
the blockchain, or the additional information in status reports, merchants can
use our techniques to quantify in real-time the threat of double-spend attacks.

Cryptography and Security