  HotStuff is a state-of-the-art Byzantine fault-tolerant consensus protocol.
It can be pipelined to build large-scale blockchains. One of its variants
called LibraBFT is adopted in Facebook's Libra blockchain. Although it is well
known that pipelined HotStuff is secure against up to $1/3$ of Byzantine nodes,
its performance in terms of throughput and delay is still under-explored. In
this paper, we develop a multi-metric evaluation framework to quantitatively
analyze pipelined \mbox{HotStuff's performance} with respect to its chain
growth rate, chain quality, and latency. We then propose two attack strategies
and evaluate their effects on the performance of pipelined HotStuff. Our
analysis shows that the chain growth rate (resp, chain quality) of pipelined
HotStuff under our attacks can drop to as low as 4/9 (resp, 12/17) of that
without attacks when $1/3$ nodes are Byzantine. As another application, we use
our framework to evaluate certain engineering optimizations adopted by
LibraBFT. We find that these optimizations make the system more vulnerable to
our attacks than the original pipelined HotStuff. Finally, we provide two
countermeasures to thwart these attacks. We hope that our studies can shed
light on the rigorous understanding of the state-of-the-art pipelined HotStuff
protocol as well as its variants.
