[Resource Topic] 2023/1869: Accountable Bulletin Boards: Definition and Provably Secure Implementation

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Accountable Bulletin Boards: Definition and Provably Secure Implementation

Authors: Mike Graf, Ralf Küsters, Daniel Rausch, Simon Egger, Marvin Bechtold, Marcel Flinspach


Bulletin boards (BB) are important cryptographic building blocks that, at their core, provide a broadcast channel with
memory. BBs are widely used within many security protocols, including secure multi-party computation protocols, e-voting systems, and electronic auctions. Even though the security of protocols crucially depends on the underlying BB, as also highlighted by recent works, the literature on constructing secure BBs is sparse. The so-far only provably secure BBs require trusted components and sometimes also networks without message loss, which makes them unsuitable for applications with particularly high security needs where these assumptions might not always be met.

In this work, we fill this gap by leveraging the concepts of accountability and universal composability (UC). More
specifically, we propose the first ideal functionality for accountable BBs that formalizes the security requirements
of such BBs in UC. We then propose Fabric$^\ast_\text{BB} as a slight extension designed on top of Fabric^\ast$, which is a variant of the prominent Hyperledger Fabric distributed ledger protocol, and show that Fabric$^\ast_\text{BB} UC-realizes our ideal BB functionality. This result makes Fabric^\ast_\text{BB} the first provably accountable BB, an often desired, but so far not formally proven property for BBs, and also the first BB that has been proven to be secure based only on standard cryptographic assumptions and without requiring trusted BB components or network assumptions. Through an implementation and performance evaluation we show that Fabric^\ast_\text{BB}$ is practical for many applications of BBs.

ePrint: https://eprint.iacr.org/2023/1869

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