The round complexity of perfectly secure general VSS

  • Authors:
  • Ashish Choudhury;Kaoru Kurosawa;Arpita Patra

  • Affiliations:
  • Applied Statistics Unit, Indian Statistical Institute Kolkata India;Department of Computer and Information Sciences, Ibaraki University, Hitachi Ibaraki, Japan;Department of Computer Science, Aarhus University Denmark

  • Venue:
  • ICITS'11 Proceedings of the 5th international conference on Information theoretic security
  • Year:
  • 2011

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Abstract

The round complexity of verifiable secret sharing (VSS) schemes has been studied extensively for threshold adversaries. In particular, Fitzi et al. showed an efficient 3-round VSS for n ≥ 3t + 1 [4], where an infinitely powerful adversary can corrupt t (or less) parties out of n parties. This paper shows that for non-threshold adversaries: 1. Two round perfectly secure VSS is possible if and only if the underlying adversary structure satisfies the Q4 condition; 2. Three round perfectly secure VSS is possible if and only if the underlying adversary structure satisfies the Q3 condition. Further as a special case of our three round protocol, we can obtain a more efficient 3-round VSS than the VSS of Fitzi et al. for n = 3t + 1. More precisely, the communication complexity of the reconstruction phase is reduced from O(n3) to O(n2). We finally point out a flaw in the reconstruction phase of the VSS of Fitzi et al., and show how to fix it.