Paper 2023/1103

Practical Large-Scale Proof-of-Stake Asynchronous Total-Order Broadcast

Abstract

We present simple and practical protocols for generating randomness as used by asynchronous total-order broadcast. The protocols are secure in a proof-of-stake setting with dynamically changing stake. They can be plugged into existing protocols for asynchronous total-order broadcast and will turn these into asynchronous total-order broadcast with dynamic stake. Our contribution relies on two important techniques. The paper ``Random Oracles in Constantinople: Practical Asynchronous Byzantine Agreement using Cryptography'' [Cachin, Kursawe, and Shoup, PODC 2000] has influenced the design of practical total-order broadcast through its use of threshold cryptography. However, it needs a setup protocol to be efficient. In a proof-of-stake setting with dynamic stake this setup would have to be continually recomputed, making the protocol impractical. The work ``Asynchronous Byzantine Agreement with Subquadratic Communication'' [Blum, Katz, Liu-Zhang, and Loss, TCC 2020] showed how to use an initial setup for broadcast to asymptotically efficiently generate sub-sequent setups. The protocol, however, resorted to fully homomorphic encryption and was therefore not practically efficient. We adopt their approach to the proof-of-stake setting with dynamic stake, apply it to the Constantinople paper, and remove the need for fully homomorphic encryption. This results in simple and practical proof-of-stake protocols. We discuss how to use the new coin-flip protocols together with DAG rider [Keidar et al., PODC 2021] and create a variant which works for dynamic proof of stake. Our method can be employed together with many further asynchronous total-order broadcast protocols.