This paper presents a partially synchronous BFT consensus protocol powered by
BBCA, a lightly modified Byzantine Consistent Broadcast (CBC) primitive. BBCA
provides a Complete-Adopt semantic through an added probing interface to allow
either aborting the broadcast by correct nodes or exclusively, adopting the
message consistently in case of a potential delivery. It does not introduce any
extra type of messages or communication cost to CBC.
BBCA is harnessed into BBCA-CHAIN to make direct commits on a chained
backbone of a causally ordered graph of blocks, without any additional voting
blocks or artificial layering. With the help of Complete-Adopt, the additional
knowledge gained from the underlying CBC completely removes the voting latency
in popular DAG-based protocols. At the same time, causal ordering allows nodes
to propose blocks in parallel and achieve high throughput.
BBCA-CHAIN thus closes up the gap between protocols built by consistent
broadcasts (e.g., Bullshark) to those without such an abstraction (e.g.,
PBFT/HotStuff), emphasizing their shared fundamental principles. Using a
Bracha-style CBC as an example, we fully specify BBCA-CHAIN with simplicity,
serving as a solid basis for high-performance replication systems (and
blockchains)