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Journal ArticleDOI

The Size of a Share Must Be Large

László Csirmaz
- 01 Sep 1997 - 
- Vol. 10, Iss: 4, pp 223-231
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TLDR
It is proved that for each n there exists an access structure on n participants so that any perfect sharing scheme must give some participant a share which is at least about $n/\log n times the secret size.
Abstract
A secret sharing scheme permits a secret to be shared among participants of an n-element group in such a way that only qualified subsets of participants can recover the secret. If any nonqualified subset has absolutely no information on the secret, then the scheme is called perfect. The share in a scheme is the information that a participant must remember. In [3] it was proved that for a certain access structure any perfect secret sharing scheme must give some participant a share which is at least 50\percent larger than the secret size. We prove that for each n there exists an access structure on n participants so that any perfect sharing scheme must give some participant a share which is at least about $n/\log n$ times the secret size.^1 We also show that the best possible result achievable by the information-theoretic method used here is n times the secret size. ^1 All logarithms in this paper are of base 2.

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Citations
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Book ChapterDOI

Secret-sharing schemes: a survey

TL;DR: This survey describes the most important constructions of secret-sharing schemes and explains the connections between secret- sharing schemes and monotone formulae and monOTone span programs, and presents the known lower bounds on the share size.
DissertationDOI

Entropy measures and unconditional security in cryptography

TL;DR: Information-theoretic meth¬ ods are used for proving the security of unconditionally secure cryptosystems, and a new information measure, smooth entropy, is introduced to quantify the number of almost uniform random bits that can be extracted from a source by probabilistic algorithms.
Journal ArticleDOI

On the information rate of perfect secret sharing schemes

TL;DR: A method to derive information-theoretical upper bounds on the optimal information rate and the optimal average information rate of perfect secret sharing schemes based on connected graphs on six vertices is discussed.
Journal ArticleDOI

Tight Bounds on the Information Rate of Secret SharingSchemes

TL;DR: It is proved that for any integer d there exists a d-regular graph for which any secret sharing scheme has information rate upper bounded by 2/(d+1), which improves on van Dijk's result dik and matches the corresponding lower bound proved by Stinson in [22].
Journal ArticleDOI

Superpolynomial Lower Bounds for Monotone Span Programs

TL;DR: The results give the first superpolynomial lower bounds for linear secret sharing schemes and show that the perfect matching function can be computed by polynomial size (non-monotone) span programs over arbitrary fields.
References
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Book

Information Theory: Coding Theorems for Discrete Memoryless Systems

TL;DR: This new edition presents unique discussions of information theoretic secrecy and of zero-error information theory, including the deep connections of the latter with extremal combinatorics.
Book ChapterDOI

Security of ramp schemes

TL;DR: A k out of n p/s/r process [AS81] is a very efficient way to convey information (k words suffice to reclaim k words), but it provides virtually no cryptographic security for the information it deals with.
Journal ArticleDOI

On the size of shares for secret sharing schemes

TL;DR: This work shows that there are access structures with four participants for which any secret sharing scheme must give to a participant a share at least 50% greater than the secret size, the first proof that there exist access structures for which the best achievable information rate is bounded away from 1.
Journal ArticleDOI

On the classification of ideal secret sharing schemes

TL;DR: In this article, the authors show a relationship between ideal secret sharing schemes and matroids, and show that the set of possible shares in a secret sharing scheme is matroid-like.