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On the Security Properties of e-Voting Bulletin Boards

2018; Springer Science+Business Media; Linguagem: Inglês

10.1007/978-3-319-98113-0_27

1611-3349

Aggelos Kiayias, Annabell Kuldmaa, Helger Lipmaa, Janno Siim, Thomas Zacharias,

Security and Verification in Computing

In state-of-the-art e-voting systems, a bulletin board (BB) is a critical component for preserving election integrity and availability. We introduce a framework for the formal security analysis of the BB functionality modeled as a distributed system. Our framework treats a secure BB as a robust public transaction ledger, defined by Garay et al. [Eurocrypt 2015], that additionally supports the generation of receipts for successful posting. Namely, in our model, a secure BB system achieves Persistence and Liveness that can be confirmable, in the sense that any malicious behavior can be detected via a verification mechanism. As a case study for our framework, we analyze security guarantees and weaknesses of the BB system of [CSF 2014]. We demonstrate an attack revealing that the said system does not achieve Confirmable Liveness in our framework, even against covert adversaries. In addition, we show that special care should be taken for the choice of the underlying cryptographic primitives, so that the claimed fault tolerance threshold of N/3 out-of N corrupted IC peers is preserved. Next, based on our analysis, we introduce a new BB protocol that upgrades the [CSF 2014] protocol. We prove that it tolerates any number less than N/3 out-of N corrupted IC peers both for Persistence and Confirmable Liveness, against a computationally bounded general Byzantine adversary. Furthermore, Persistence can also be Confirmable, if we distribute the AB (originally a centralized entity in [CSF 2014]) as a replicated service with honest majority.