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Threshold Secret Sharing Requires a Linear Size Alphabet

  • Andrej Bogdanov
  • Siyao Guo
  • Ilan Komargodski
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9986)

Abstract

We prove that for every n and \(1< t < n\) any t-out-of-n threshold secret sharing scheme for one-bit secrets requires share size \(\log (t + 1)\). Our bound is tight when \(t = n - 1\) and n is a prime power. In 1990 Kilian and Nisan proved the incomparable bound \(\log (n - t + 2)\). Taken together, the two bounds imply that the share size of Shamir’s secret sharing scheme (Comm. ACM ’79) is optimal up to an additive constant even for one-bit secrets for the whole range of parameters \(1< t < n\).

More generally, we show that for all \(1< s< r < n\), any ramp secret sharing scheme with secrecy threshold s and reconstruction threshold r requires share size \(\log ((r + 1)/(r - s))\).

As part of our analysis we formulate a simple game-theoretic relaxation of secret sharing for arbitrary access structures. We prove the optimality of our analysis for threshold secret sharing with respect to this method and point out a general limitation.

Keywords

Secret Sharing Access Structure Winning Strategy Secret Sharing Scheme Threshold Scheme 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

We thank Moni Naor for telling us about the work of Kilian and Nisan. We thank the anonymous reviewers for their useful advice.

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Copyright information

© International Association for Cryptologic Research 2016

Authors and Affiliations

  1. 1.Chinese University of Hong KongHong KongChina
  2. 2.New York UniversityNew YorkUSA
  3. 3.Weizmann Institute of ScienceRehovotIsrael

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