  Cryptocurrencies, based on and led by Bitcoin, have shown promise as
infrastructure for pseudonymous online payments, cheap remittance, trustless
digital asset exchange, and smart contracts. However, Bitcoin-derived
blockchain protocols have inherent scalability limits that trade-off between
throughput and latency and withhold the realization of this potential.
  This paper presents Bitcoin-NG, a new blockchain protocol designed to scale.
Based on Bitcoin's blockchain protocol, Bitcoin-NG is Byzantine fault tolerant,
is robust to extreme churn, and shares the same trust model obviating
qualitative changes to the ecosystem.
  In addition to Bitcoin-NG, we introduce several novel metrics of interest in
quantifying the security and efficiency of Bitcoin-like blockchain protocols.
We implement Bitcoin-NG and perform large-scale experiments at 15% the size of
the operational Bitcoin system, using unchanged clients of both protocols.
These experiments demonstrate that Bitcoin-NG scales optimally, with bandwidth
limited only by the capacity of the individual nodes and latency limited only
by the propagation time of the network.
