Unconditional secure conference key distribution schemes with disenrollment capability

A conference key distribution scheme with disenrollment capability is a method to distribute pieces of information among a set of users in such a way that each group of them can compute a common key to be used for secure communication. In such a scheme any user can be disenrolled. After each disenrollment, although the disenrolled user reveals his private information, the security of the scheme remains unchanged. The scheme is unconditional secure if any adversary coalition has no information on the common key even though it has access to an infinite computational power.

In this paper we model the problem of unconditionally secure conference key distribution schemes with disenrollment capability using an information theoretical framework. We prove tight lower bounds on the size of information each user in the scheme has to keep secret.