Brief Announcement: Twins – BFT Systems Made Robust

Authors Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, Dahlia Malkhi

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Author Details

Shehar Bano
  • Facebook Novi, London, UK
Alberto Sonnino
  • Facebook Novi, London, UK
Andrey Chursin
  • Facebook Novi, Menlo Park, CA, USA
Dmitri Perelman
  • Facebook Novi, Menlo Park, CA USA
Zekun Li
  • Facebook Novi, Menlo Park, CA, USA
Avery Ching
  • Facebook Novi, Menlo Park, CA, USA
Dahlia Malkhi
  • Diem Association, Wilmington, DE, USA
  • Facebook Novi, Menlo Park, CA, USA


The authors would like to thank Ben Maurer, David Dill, Daniel Xiang, Kartik Nayak, and Ling Ren for feedback on late manuscript, and George Danezis for comments on early manuscript. We also thank the Novi Research and Engineering teams for valuable feedback.

Cite AsGet BibTex

Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi. Brief Announcement: Twins – BFT Systems Made Robust. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 46:1-46:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)


Twins is an effective strategy for generating test scenarios with Byzantine [Lamport et al., 1982] nodes in order to find flaws in Byzantine Fault Tolerant (BFT) systems. Twins finds flaws in the design or implementation of BFT protocols that may cause correctness issues. The main idea of Twins is the following: running twin instances of a node that use correct, unmodified code and share the same network identity and credentials allows to emulate most interesting Byzantine behaviors. Because a twin executes normal, unmodified node code, building Twins only requires a thin wrapper over an existing distributed system designed for Byzantine tolerance. To emulate material, interesting scenarios with Byzantine nodes, it instantiates one or more twin copies of the node, giving the twins the same identities and network credentials as the original node. To the rest of the system, the node and all its twins appear indistinguishable from a single node behaving in a "questionable" manner. This approach generates many interesting Byzantine behaviors, including equivocation, double voting, and losing internal state, while forgoing uninteresting behavior scenarios that can be filtered at the transport layer, such as producing semantically invalid messages. Building on configurations with twin nodes, Twins systematically generates scenarios with Byzantine nodes via enumeration over protocol rounds and communication patterns among nodes. Despite this being inherently exponential, one new flaw and several known flaws were materialized by Twins in the arena of BFT consensus protocols. In all cases, protocols break within fewer than a dozen protocol rounds, hence it is realistic for the Twins approach to expose the problems. In two of these cases, it took the community more than a decade to discover protocol flaws that Twins would have surfaced within minutes. Additionally, Twins has been incorporated into the continuous release testing process of a production setting (DiemBFT) in which it can execute 44M Twins-generated scenarios daily.

Subject Classification

ACM Subject Classification
  • Security and privacy → Distributed systems security
  • Distributed Systems
  • Byzantine Fault Tolerance
  • Real-World Deployment


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