New bounds on the information rate of secret sharing schemes

A secret sharing scheme permits a secret to be shared among participants in such a way that only qualiied subsets of participants can recover the secret, but any non-qualiied subset has absolutely no information on the secret. In this paper we derive new limitations on the information rate of secret sharing schemes, that measures how much information is being distributed as shares as compared to the size of the secret key, and the average information rate, that is the ratio between the secret size and the arithmetic mean of the size of the shares. By applying the substitution technique, we are able to construct many new examples of access structures where the information rate is bounded away from 1. The substitution technique is a method to obtain a new access structure by replacing a participant in a previous structure with a new access structure.