Secret sharing in user hierarchy represents a challenging area for research. A lot of research work has already been done in this direction. This book presents a novel approach to share a secret among a hierarchy of users while overcoming the limitations of the already existing mechanisms. Traditional (k + 1; n)-threshold secret sharing, is secure as long as an adversary can compromise not more than k secret shares. But in real life it is often feasible for an adversary to obtain more than k shares over a long period of time. Here we present a way to overcome this vulnerability, while...