  Traditional blockchain design gives miners or validators full control over
transaction ordering, i.e., they can freely choose which transactions to
include or exclude, as well as in which order. While not an issue initially,
the emergence of decentralized finance has introduced new transaction order
dependencies allowing parties in control of the ordering to make a profit by
front-running others' transactions. In this work, we present the Decentralized
Clock Network, a new approach for achieving fair transaction ordering. Users
submit their transactions to the network's clocks, which run an agreement
protocol that provides each transaction with a timestamp of receipt which is
then used to define the transactions' order. By separating agreement from
ordering, our protocol is efficient and has a simpler design compared to other
available solutions. Moreover, our protocol brings to the blockchain world the
paradigm of asynchronous fallback, where the algorithm operates with stronger
fairness guarantees during periods of synchronous use, switching to an
asynchronous mode only during times of increased network delay.
