On Ideal Secret-Sharing Schemes for k-homogeneous access structures
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A k-uniform hypergraph is a hypergraph where each k-hyperedge has exactly k vertices. A k-homogeneous access structure is represented by a k-uniform hypergraph ℋ, in which the participants correspond to the vertices of hypergraph ℋ. A set of vertices can reconstruct the secret value from their shares if they are connected by a k-hyperedge, while a set of non-adjacent vertices does not obtain any information about the secret. One parameter for measuring the efficiency of a secret sharing scheme is the information rate, defined as the ratio between the length of the secret and the maximum length of the shares given to the participants. Secret sharing schemes with an information rate equal to one are called ideal secret sharing schemes. An access structure is considered ideal if an ideal secret sharing scheme can realize it. Characterizing ideal access structures is one of the important problems in secret sharing schemes. The characterization of ideal access structures has been studied by many authors <cit.>. In this paper, we characterize ideal k-homogeneous access structures using the independent sequence method. In particular, we prove that the reduced access structure of Γ is an (k, n)-threshold access structure when the optimal information rate of Γ is larger than k-1/k, where Γ is a k-homogeneous access structure satisfying specific criteria.
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