Optimum traitor tracing and asymmetric schemes

Abstract

A traceability scheme is a broadcast encryption scheme such that a data supplier T can trace malicious authorized users (traitors) who gave a decryption key to an unauthorized user (pirate). This paper first derives lower bounds on the sizes of keys and ciphertexts. These bounds are all tight because an optimum one-time use scheme is also presented. We then propose a multiple-use scheme which approximately meets our bounds. This scheme is proven to be secure as well as much more efficient than the schemes by Chor, Fiat and Naor. Finally, practical types of asymmetric schemes with arbiter are discussed in which T cannot frame any authorized user as a traitor.