Publicly Verifiable Zero Knowledge from (Collapsing) Blockchains

Alessandra Scafuro*, Luisa Siniscalchi, Ivan Visconti

*Corresponding author for this work

Research output: Contribution to book/anthology/report/proceedingArticle in proceedingsResearchpeer-review

Abstract

Publicly Verifiable Zero-Knowledge proofs are known to exist only from setup assumptions such as a trusted common reference string or a random oracle. Unfortunately, the former requires a trusted party while the latter does not exist. Blockchains are distributed systems that already exist and provide certain security properties (under some honest majority assumption), hence, a natural recent research direction has been to use a blockchain as an alternative setup assumption. In TCC 2017 Goyal and Goyal proposed a construction of a publicly verifiable zero-knowledge (pvZK) proof system for some proof-of-stake blockchains. The zero-knowledge property of their construction however relies on some additional and not fully specified assumptions about the current and future behavior of honest blockchain players. In this paper we provide several contributions. First, we show that when using a blockchain to design a provably secure protocol, it is dangerous to rely on demanding additional requirements on behaviors of the blockchain players. We do so by showing an “attack of the clones” whereby a malicious verifier can use a smart contract to slyly (not through bribing) clone capabilities of honest stakeholders and use those to invalidate the zero-knowledge property of the proof system by Goyal and Goyal. Second, we propose a new publicly verifiable zero-knowledge proof system that relies on non-interactive commitments and on an assumption on the min-entropy of some blocks appearing on the blockchain. Third, motivated by the fact that blockchains are a recent innovation and their resilience in the long run is still controversial, we introduce the concept of collapsing blockchain, and we prove that the zero-knowledge property of our scheme holds even if the blockchain eventually becomes insecure and all blockchain players eventually become dishonest.

Original languageEnglish
Title of host publicationPublic-Key Cryptography – PKC 2021 : 24th IACR International Conference on Practice and Theory of Public Key Cryptography, Virtual Event, May 10–13, 2021, Proceedings, Part II
EditorsJuan A. Garay
Number of pages30
PublisherSpringer Science and Business Media Deutschland GmbH
Publication date2021
Pages469-498
ISBN (Print)9783030752477
DOIs
Publication statusPublished - 2021
Event24th IACR International Conference on Practice and Theory of Public Key Cryptography, PKC 2021 - Virtual, Online
Duration: 10 May 202113 May 2021

Conference

Conference24th IACR International Conference on Practice and Theory of Public Key Cryptography, PKC 2021
CityVirtual, Online
Period10/05/202113/05/2021
SeriesLecture Notes in Computer Science
VolumeLNCS 12711
ISSN0302-9743

Keywords

  • (Collapsing) blockchain
  • Publicly verifiable zero knowledge

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