Key preassigned traceability schemes for broadcast encryption

Abstract

Traceability schemes for broadcast encryption are defined by Chor, Fiat and Naor in [6] to protect against a possible coalition of users producing an illegal decryption key. Their scheme was then generalized by Stinson and Wei in [17]. These schemes assume that every user can decrypt the secret value. In this paper we discuss key preassigned traceability schemes, in which only the users in a specified privileged subset can decrypt. A new scheme is presented in this paper, which has better traceability than previous schemes. We also present a new threshold traceability scheme by using ramp scheme. All the constructions are explicit and could be implemented easily.