Steelhead improves blockchain consensus for changing networks
Steelhead: Interleaving Partially Synchronous and Asynchronous Commit Rules on a Shared DAG
Distributed, Parallel, and Cluster ComputingCryptography and Security
Summary
Consensus protocols help computers agree on shared information, even if the network is slow or faulty. The authors designed Steelhead, which mixes two ways of deciding agreement—one that works fast when the network is stable and one that keeps going even when it’s unreliable. Steelhead uses a shared record of decisions and only extra randomness when needed, making it efficient and reliable. Their tests show it adapts quickly to network changes without losing agreement or speed.
What this means in practice
- •For blockchain developers: Build faster and more resilient blockchain systems that adapt automatically to network delays and failures.
- •For distributed system engineers: Design fault-tolerant distributed ledgers combining fast operation in good networks with guaranteed progress under poor conditions.
Authors
George Danezis, Zeno De Angeli, Philipp Jovanovic, Lefteris Kokoris-Kogias, Markus Legner, Alberto Sonnino
Abstract
Dual-mode consensus protocols are fast when the network is partially synchronous and remain live under asynchrony. We introduce Steelhead, a dual-mode mechanism that composes a partially synchronous and an asynchronous commit rule over one DAG: every k-th round is decided by the asynchronous rule, whose leader a common coin reveals after the votes, and all other rounds by the partially synchronous rule. Every interval, validators replay the committed DAG under each candidate period, adopt the one with the fewest expected message delays, and fall back to k = 1 when the output stalls; the asynchronous rule applied to the coin rounds alone keeps the protocol live. Steelhead sends no message beyond the DAG's blocks, not even to agree on the period, and opens a coin only on the rounds that need a hidden leader. It is generic over pairs of DAG commit rules that share a committee; we instantiate it with Mysticeti and Mahi-Mahi at n >= 3f+1 and with the two variants of BlueBottle at n >= 5f+1. We prove it safe and live, and provide mechanized proofs in Lean 4. In simulation, Steelhead matches the partially synchronous protocol in a healthy network, stays close to the asynchronous one when network conditions stall the partially synchronous one, and adapts quickly in both directions.