[Resource Topic] 2024/879: Consistency-or-Die: Consistency for Key Transparency

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Consistency-or-Die: Consistency for Key Transparency

Authors: Joakim Brorsson, Elena Pagnin, Bernardo David, Paul Stankovski Wagner


In this paper we point out the problem of insufficient tools for protecting against split-view attacks in Key Transparency protocols, and propose a solution to fill the void. We discuss why current approaches are not suitable and then propose a novel notion, GOD-less broadcast, that solves the issue. Like conventional notions of broadcast, GOD-less broadcast guarantees consistency. However, it does not provide Guaranteed Output Delivery (GOD). We provide an efficient realization of this new notion using a hidden committee of randomly selected and initially undisclosed users which endorse the current view. We also introduce and analyze a new concept of a quorum which ensures consistency among all honest active users. Our GOD-less broadcast protocol is practical and applicable to existing large scale Key Transparency systems, e.g. the Key Transparency used in WhatsApp.

ePrint: https://eprint.iacr.org/2024/879

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