Repositori URV

Identifier: imarina:9242146

Handle: https://hdl.handle.net/20.500.11797/imarina9242146

Authors:
Farras O

Abstract:
A secret sharing scheme is ideal if the size of each share is equal to the size of the secret. Brickell and Davenport showed that the access structure of an ideal secret sharing scheme is determined by a matroid. Namely, the minimal authorized subsets of an ideal secret sharing scheme are in correspondence with the circuits of a matroid containing a fixed point. In this case, we say that the access structure is a matroid port. It is known that, for an access structure, being a matroid port is not a suficient condition to admit an ideal secret sharing scheme. In this work we present a linear secret sharing scheme construction for ports of matroids of rank 3 in which the size of each share is at most n times the size of the secret. Using the previously known secret sharing constructions, the size of each share was O(n2= log n) the size of the secret. Our construction is extended to ports of matroids of any rank k 2, obtaining secret sharing schemes in which the size of each share is at most nk-2 times the size of the secret. This work is complemented by presenting lower bounds: There exist matroid ports that require (Fq; )-linear secret schemes with total information ratio (2n=2=n3=4p log q). © 2020 Institute of Information Theory and Automation of The Czech Academy of Sciences. All rights reserved.