  Despite their development for over a decade, a key problem blockchains are
still facing is scalability in terms of throughput, typically limited to a few
transactions per second. A fundamental factor limiting this metric is the
propagation latency of blocks through the underlying peer-to-peer network,
which is typically constructed by means of random connectivity. Disseminating
blocks fast improves not only the transaction throughput, but also the security
of the system as it reduces the probability of forks. In this paper we present
CougaR: a simple yet efficient, eclipse-resistant, decentralized protocol that
substantially reduces the block dissemination time in blockchain networks.
CougaR's key advantages stem from its link selection policy, which combines a
network latency criterion with randomness to offer fast and reliable block
dissemination to the entire network. Moreover, CougaR is eclipse-resistant by
design, as nodes are protected from having all their links directly or
indirectly imposed on them by others, which is the typical vulnerability
exploited to deploy eclipse attacks. We rigorously evaluate CougaR by an
extensive set of experiments, both against a wide spectrum of parameter
settings, and in comparison to the current state of the art.
