DAG-based Byzantine Fault Tolerant (BFT) protocols provide high-throughput consensus under partial synchrony, but existing DAG protocols still require at least a three-message delay to commit decisions.
In contrast, existing Fast-Path BFT protocols can achieve optimal termination with a two-message delay under favorable conditions, though they do not naturally extend to DAGs.
In this seminar we present FinWhale, the first DAG-based BFT protocol with a two-message delay fast path.
FinWhale extends the Mysticeti protocol with a novel fast-path commit mechanism that safely coexists with the protocol’s original slow-path rules.
To preserve safety across different local DAG views, we introduce new commit structures based on fast-path evidence blocks that enable validators to combine fast-path and slow-path reasoning consistently.
FinWhale operates in the partially synchronous model with $n=3f+2p-1$ validators; this matches the known lower-bound for fast Byzantine consensus.
The protocol tolerates up to $f$ Byzantine faults and achieves fast termination whenever at most $p$ validators fail during the fast path ($1 \leq p\leq f$).
Our results show that optimal-latency fast paths can be integrated into uncertified DAG consensus protocols.