In this paper we propose a novel solution to the problem of providing trusted third party services, such as the management of cryptographic keys for end-to-end encryption, in a way that meets legal requirements for warranted interception. Also included is a discussion of what might be a reasonable set of requirements for international provision of such services, as well as some analysis of the cryptographic properties of the architecture and how it might operate in practice.

In an ideal secret sharing scheme, the access structure is uniquely determined by its minimal sets Δs. The purpose of this paper is to characterise Δs. We introduce the concept of strong connectivity and show that under this equivalence relation, an ideal secret sharing scheme decomposes into threshold schemes. We also give a description of the minimal sets that span the strong connectivity classes. As a result we obtain a necessary condition on the types of subsets that are allowed in an ideal access structure as well as an upper bound on the number of such access structures.

The purpose of this paper is to prove the equivalence of perfect authentication schemes and maximum distance separable codes.