Abstract
In this paper, we discuss methods by which a trusted authority can broadcast a message over a network, so that each member of a specified privileged subset of users can decrypt this message to compute a secret key. In contrast with previously constructed schemes, it is possible for the different privileged users to recover different keys from the broadcast message. Moreover, this is done in such a way that no coalition is able to recover any information on any of the keys they are not supposed to know. The schemes also do not require addressing, so user anonymity is maintained. The problem is studied using the tools of information theory, so the security provided is unconditional (i.e., not based on any computational assumption). Some useful schemes are presented and compared to previously known schemes.
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