Broadcast encryption with both temporary and permanent revocation

Broadcast encryption enables a sender to broadcast data that only an authorized set of users can decrypt and is therefore an essential component of secure content distribution. Public key broadcast encryption separates the roles of a key manager who provides keys to users and content providers who distribute content to users. This separation is useful for flexible content distribution and for simplifying the process of additional content providers joining the network. A content provider or key manager can control the authorized set of users by user revocation which has two types, temporary revocation and permanent revocation. A content provider sending a message can determine the set of users authorized for the message by using temporary revocation. A key manager can use permanent revocation to remove a user from the set of authorized users as a better alternative to temporarily revoking the user in all subsequent messages. In this paper we present the first public-key, broadcast encryption scheme that achieves both temporary and permanent revocation and has essentially the same performance as state of the art schemes that achieve only one of the two types of revocation. The scheme combines and optimizes the broadcast encryption systems of Delerablée et al. (Pairing 2007) and Lewko et al. (Security and Privacy 2010) and is generically secure over groups that support bilinear maps.