Broadcast Encryption with Multiple Trust Authorities

In this paper we extend the notion of hierarchical identitybased encryption with wildcards (WIBE) from the domain of a single Trusted Authority (TA) to a setting with multiple, independent Trusted Authorities each with their own WIBE. In this multi-trust-authority WIBE environment, a group of TA’s may form coalitions, enabling secure communication across domains. These coalitions can be created in an ad-hoc fashion and membership of one coalition does not give a trust authority any advantage in decrypting a ciphertext for a different coalition. This allows the broadcast of confidential messages to large groups of users within a coalition with a single ciphertext. We provide a full syntax and security model for multi-trust-authority WIBEs, and give a constructions based on the Boneh-Boyen WIBE scheme for both passive and active attackers.