A tau-restricted key agreement scheme

A one-restricted key agreement scheme is a method by which initially a trus ted authority distributes private individual pieces of information to a set of users. Later, each member of any group of users of a given size, referr ed to as a conference, can compute a common key by exchanging messages over a broadcast channel all users have access to. Such schemes can be used to establish only one common key. In this paper we analyse tau-restricted key agreement schemes. Such schemes allow the computation of up to tau common k eys for tau distinct conferences. For certain values of the parameters the scheme that we propose distributes less information than the trivial one ob tained by considering tau copies of a one-restricted scheme.