Skipping, Cascade, and Combined Chain Schemes for Broadcast Encryption

We develop a couple of new methods to reduce transmission overheads in broadcast encryption. The methods are based on the idea of assigning one key per each partition using one-way key chains after partitioning the users. One method adopts skipping chains on partitions containing up to p revoked users and the other adopts cascade chains on partitions with layer structure. The scheme using the former reduces the transmission overhead down to p+1 asymptotically as r grows, and the scheme using the latter keeps the transmission overhead very small when r approaches 0, where r is the number of revoked users. Combining the two schemes, we propose a new broadcast encryption scheme with least transmission overhead. Our schemes also possess a remarkable feature that any number of new users can join at any time without key update, which is not available for most of known practical schemes

Optimization techniques and new methods for boradcast encryption and traitor tracing schemes

Ankara : The Department of Computer Engineering and the Graduate School of Engineering and Science of Bilkent University, 2012.Thesis (Ph. D.) -- Bilkent University, 2012.Includes bibliographical refences.In the last few decades, the use of digital content increased dramatically. Many forms of digital products in the form of CDs, DVDs, TV broadcasts, data over the Internet, entered our life. Classical cryptography, where encryption is done for only one recipient, was not able to handle this change, since its direct use leads to intolerably expensive transmissions. Moreover, new concerns regarding the commercial aspect arised. Since digital commercial contents are sold to various customers, unauthorized copying by malicious actors became a major concern and it needed to be prevented carefully. Therefore, a new research area called digital rights management (DRM) has emerged. Within the scope of DRM, new cryptographic primitives are proposed. In this thesis, we consider three of these: broadcast encryption (BE), traitor tracing (TT), and trace and revoke (T&R) schemes and propose methods to improve the performances and capabilities of these primitives. Particularly, we first consider profiling the recipient set in order to improve transmission size in the most popular BE schemes. We then investigate and solve the optimal free rider assignment problem for one of the most efficient BE schemes so far. Next, we attempt to close the non-trivial gap between BE and T&R schemes by proposing a generic method for adding traitor tracing capability to BE schemes and thus obtaining a T&R scheme. Finally, we investigate an overlooked problem: privacy of the recipient set in T&R schemes. Right now, most schemes do not keep the recipient set anonymous, and everybody can see who received a particular content. As a generic solution to this problem, we propose a method for obtaining anonymous T&R scheme by using anonymous BE schemes as a primitive.Ak, MuratPh.D