Decentralized Seminar Series at UW Madison

Talk: HotStuff-2: Optimal Two-Phase Responsive BFT

Speaker: Dahlia Malkhi (Chainlink)
Date: Mon, 04/03/23
Time: 12pm
Location: Online


We observe that it is possible to solve partially-synchronous BFT and simultaneously achieves worst-case communication, optimistically linear communication, a two-phase commit regime within a view, and optimistic responsiveness. Prior work falls short in achieving one or more of these properties, e.g., the most closely related work, HotStuff, requires a three-phase view while achieving all other properties. We demonstrate that these properties are achievable through a two-phase HotStuff variant named HotStuff-2. The quest for two-phase HotStuff variants that achieve all the above desirable properties has been long, producing a series of results that are yet sub-optimal and, at the same time, are based on somewhat heavy hammers. HotStuff-2 demonstrates that none of these are necessary: HotStuff-2 is remarkably simple, adding no substantive complexity to the original HotStuff protocol. The main takeaway is that two phases are enough for BFT after all.


Dr. Malkhi’s research over two decades spans broad aspects of reliability and security of distributed systems, recently with focus on blockchains and advances in financial technology. Her work resulted in over 150 publications as well as a strong impact on computing technology.

Presently, Malkhi serves as Distinguished Scientist of Chainlink Labs (since 2022). From 2019 to 2022, Malkhi served three roles in the Diem(Libra) project: CTO at the Diem Association, Lead Maintainer of the Diem open-source project, and Lead Researcher at Novi. In 2014, after the closing of the Microsoft Research Silicon Valley lab, Malkhi co-founded VMware Research and became a Principal Researcher at VMware until June 2019. Prior to that, Malkhi was a partner principal researcher at Microsoft Research, 2004-2014; a tenured Associate Professor (promoted 2003) of the Hebrew University of Jerusalem, 1999-2007; and a senior researcher at AT&T Labs, 1995-1999.