  Low latency is one of the most desirable features of partially synchronous
Byzantine consensus protocols. Existing low-latency protocols have achieved
consensus with just two communication steps by reducing the maximum number of
faults the protocol can tolerate (from $f = \frac{n-1}{3}$ to $f =
\frac{n+1}{5}$), \textcolor{black}{by relaxing protocol safety guarantees}, or
by using trusted hardware like Trusted Execution Environment. Furthermore,
these two-step protocols don't support rotating leaders and low-cost view
change (leader replacement), which are important features of many blockchain
use cases. In this paper, we propose a protocol called VBFT which achieves
consensus in just two communication steps without sacrificing desirable
features. In particular, VBFT tolerates $f = \frac{n-1}{3}$ faults (which is
the best possible), guarantees strong safety for honest leaders, and requires
no trusted hardware. Moreover, VBFT supports leader rotation and low-cost view
change, thereby improving prior art on multiple axes.
