  Proof-of-work blockchains must implement a difficulty adjustment algorithm
(DAA) in order to maintain a consistent inter-arrival time between blocks.
Conventional DAAs are essentially feedback controllers, and as such, they are
inherently reactive. This approach leaves them susceptible to manipulation and
often causes them to either under- or over-correct. We present Bonded Mining, a
proactive DAA that works by collecting hash rate commitments secured by bond
from miners. The difficulty is set directly from the commitments and the bond
is used to penalize miners who deviate from their commitment. We devise a
statistical test that is capable of detecting hash rate deviations by utilizing
only on-blockchain data. The test is sensitive enough to detect a variety of
deviations from commitments, while almost never misclassifying honest miners.
We demonstrate in simulation that, under reasonable assumptions, Bonded Mining
is more effective at maintaining a target block time than the Bitcoin Cash DAA,
one of the newest and most dynamic DAAs currently deployed. In this preliminary
work, the lowest hash rate miner our approach supports is 1% of the total and
we directly consider only two types of fundamental attacks. Future work will
address these limitations.
