Hydrozoan: Latency-Adaptive DAG Consensus under Mixed Byzantine and Crash Faults
Hydrozoan is a DAG consensus protocol that commits in two or three delays under mixed Byzantine and crash faults.
Hydrozoan is a DAG-based consensus protocol for n = 3f+c+2p+1 validators that tolerates f Byzantine and c crash faults. Leaders commit in two message delays when at most p validators are faulty and in three delays otherwise, using one DAG, no extra messages, and no view changes. Optimal-Hydrozoan tolerates one additional fast-path fault and matches a known lower bound; both protocols' safety and liveness are machine-checked in Lean 4. A geo-distributed evaluation matches Mysticeti's throughput and commits about 25% faster when the fast quorum sits in low-latency regions.
- Fast path commits in two message delays when at most p validators are faulty.
- Otherwise it commits in three delays on the same DAG, with no extra messages.
- The validator count is n = 3f+c+2p+1 under hybrid Byzantine and crash faults.
- Safety and liveness of both variants are machine-checked in Lean 4.
- Evaluation matches Mysticeti throughput and is about 25% faster in favorable regions.
Full article270 words · extracted from arxiv.org · click to collapse
DAG-based consensus protocols can achieve great throughput and the optimal three-message-delay limit for n = 3f+1 consensus. While two-delay protocols exist, they pay with reduced resilience (requiring 5f+1-style committees) or rely on fallbacks that sacrifice the DAG's high throughput. This paper introduces Hydrozoan, the first DAG protocol with a dual commit path under a hybrid fault model of f Byzantine and c crashed validators, on n = 3f+c+2p+1 validators. Leaders commit in two message delays whenever at most p validators are faulty, and in three otherwise, with no extra messages, no view changes, and multiple leaders per round. Both paths are evaluated on the same DAG, using a novel graded indirect rule to reconcile them so that every honest validator reaches the same decision. We show that under geo-distributed conditions, which path is faster is a property of geography rather than the protocol, as rounds reaching a remote region cost far more than those that do not. The (f, c, p) knobs place the fast quorum where the deployment requires it, allowing a commit in two message delays. If misconfigured, Hydrozoan can still commit in three message delays: Hydrozoan commits on whichever path fires first. We also present Optimal-Hydrozoan, a variant that tolerates one more fault on the fast path, the first construction to match the known lower bound. The safety and liveness of both protocols are machine-checked in Lean 4. Our geo-distributed evaluation shows that Hydrozoan matches Mysticeti's throughput, commits ~25% faster when the fast quorum fits fast regions, and falls back to three message delays when it does not or past p faults, where existing two-delay protocols stall.
Text extracted automatically; images, tables and formatting may be missing. Original: https://arxiv.org/abs/2609.25918