New results on non-perfect sharing of multiple secrets

  • Authors:
  • Alfredo De Santis;Barbara Masucci

  • Affiliations:
  • Dipartimento di Informatica ed Applicazioni, Universití di Salerno, 84081 Baronissi (SA), Italy;Dipartimento di Informatica ed Applicazioni, Universití di Salerno, 84081 Baronissi (SA), Italy

  • Venue:
  • Journal of Systems and Software
  • Year:
  • 2007

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Abstract

A non-perfect secret sharing scheme is a method to distribute a secret among a set of participants, in such a way that some qualified subsets of participants, pooling together their information, can reconstruct the secret, whereas, other subsets of participants may have some information about the secret. In this journal, Feng et al. (2005) [A new multi-secret image sharing scheme using Lagrange's interpolation. The Journal of Systems and Software, 76 (3), 327-339] recently considered the situation in which there are many secrets to be shared among a set of participants, in such a way that each qualified subset of participant can reconstruct a different secret. They proposed a polynomial-based construction using as a main tool a particular sequence of participants, called a sharing-circle, and having the feature that the smaller the length of the sharing-circle, the smaller the size of the shares distributed to participants. They proposed a simple recursive algorithm to find a minimal length sharing-circle. Since their algorithm is exponential-time, they left the task of finding a better one as an open problem. In this paper we first answer their question, showing that a polynomial-time algorithm computing a minimal-length sharing-circle is unlikely to exist. Indeed, we prove that the problem of finding a sharing-circle having minimal length is NP-hard. Afterwards, we propose a construction which is simpler than the one of Feng et al. and that does not require the participants to perform polynomial interpolation in order to reconstruct the secrets. Moreover, our scheme distributes shares having a smaller size.