On Linear Secret Sharing for Connectivity in Directed Graphs

  • Authors:
  • Amos Beimel;Anat Paskin

  • Affiliations:
  • Dept. of computer science, Ben-Gurion University, Beer Sheva, Israel;Dept. of computer science, Technion, Haifa, Israel

  • Venue:
  • SCN '08 Proceedings of the 6th international conference on Security and Cryptography for Networks
  • Year:
  • 2008

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Abstract

In this work we study linear secret sharing schemes for s-tconnectivity in directed graphs. In such schemes the parties are edges of a complete directed graph, and a set of parties (i.e., edges) can reconstruct the secret if it contains a path from node sto node t. We prove that in every linear secret sharing scheme realizing the st-con function on a directed graph with nedges the total size of the shares is ï戮驴(n1.5). This should be contrasted with s-tconnectivity in undirected graphs, where there is a scheme with total share size n. Our result is actually a lower bound on the size monotone span programs for st ï戮驴 con, where a monotone span program is a linear-algebraic model of computation equivalent to linear secret sharing schemes. Our results imply the best known separation between the power of monotone and non-monotone span programs. Finally, our results imply the same lower bounds for matching.